Land and Food Systems, Faculty of
DSpace
UBCV
Shojaei, Maryam
Master of Science - MSc
University of British Columbia
There has been a burgeoning interest in blueberry consumption due to its nutritional and health benefits. However, blueberries are very perishable due to their susceptibility to water loss and mould deterioration, affecting their quality and shelf-life. The objective of this study was to optimize innovative post-harvest strategies, pulsed light (PL) and controlled atmosphere storage (CAS) to improve the quality and shelf-life of highbush blueberries grown in BC. We hypothesized that the post-harvest shelf-life of highbush blueberries could be extended through using PL and CAS while both strategies meet the consumer demand for natural, and minimally processed foods. In this study, the effect of four CAS conditions (8kPa CO2 + 1.5kPa O2; 8kPa CO2 + 10kPa O2; 15kPa CO2 + 1.5kPa O2; 15kPa CO2 + 10kPa O2) and three PL treatments with doses of 3, 6, and 9 Jcm-2 were assessed using for their impact on the final quality and shelf-life of highbush blueberries (cv. Draper). In addition, the berry quality parameters (colour, firmness, weight loss, and rot incidence), antioxidant activity, pH, titratable acidity, and total soluble solids, and shelf-life were analyzed during six weeks. All CAS and PL treatments showed decreased weight loss compared to the regular atmosphere storage at the end of the storage. PL doses of 9 Jcm-2 showed less rot incidence, and PL doses of 6 Jcm-2 showed higher firmness compared to control; however, no significant difference (p < 0.05) has been observed in PL treated blueberries in all CAS in terms of firmness and rot incidence compared to control by week six. Increasing PL doses decreased antioxidant activity during storage time. Total soluble solids (TSS) and total acidity (TA) increased with increasing PL doses in the lower O2 concentration storage. Results showed that treating blueberries with PL doses of 6 and 9 Jcm-2 in CAS of 10kPa O2 and 8kPa CO2 provided the optimal conditions for maintaining the blueberries’ quality traits after four weeks. These findings can help increase the quality and shelf-life of blueberries, while minimizing their environmental impact, which could significantly impact the industry market, locally and globally.
i Application of Pulsed Light and Controlled Atmosphere Storage for Extension of Post-Harvest Quality and Shelf-life of Highbush Blueberries (cv. Draper) by Maryam Shojaei A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in The Faculty of Graduate and Postdoctoral Studies (Food Science) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) December 2021 ©Maryam Shojaei, 2021 ii The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, a thesis entitled: Application of Pulsed Light and Controlled Atmosphere Storage for Extension of Post-Harvest Quality and Shelf-life of Highbush Blueberries (cv. Draper) Submitted by Maryam Shojaei in partial fulfillment of the requirement for the degree of Master of Science in Food Science Supervisory Committee Members: Dr. Anubhav Pratap-Singh, Assistant Professor, Food Science, UBC Supervisor Dr. David D. Kitts, Professor, Food Science, UBC Supervisory Committee Member Dr. Simone Diego Castellarin, Associate Professor, Plant Science, UBC Supervisory Committee Member iii Abstract There has been a burgeoning interest in blueberry consumption due to its nutritional and health benefits. However, blueberries are very perishable due to their susceptibility to water loss and mould deterioration, affecting their quality and shelf-life. The objective of this study was to optimize innovative post-harvest strategies, pulsed light (PL) and controlled atmosphere storage (CAS) to improve the quality and shelf-life of highbush blueberries grown in BC. We hypothesized that the post-harvest shelf-life of highbush blueberries could be extended through using PL and CAS while both strategies meet the consumer demand for natural, and minimally processed foods. In this study, the effect of four CAS conditions (8kPa CO2 + 1.5kPa O2; 8kPa CO2 + 10kPa O2; 15kPa CO2 + 1.5kPa O2; 15kPa CO2 + 10kPa O2) and three PL treatments with doses of 3, 6, and 9 Jcm-2 were assessed using for their impact on the final quality and shelf-life of highbush blueberries (cv. Draper). In addition, the berry quality parameters (colour, firmness, weight loss, and rot incidence), antioxidant activity, pH, titratable acidity, and total soluble solids, and shelf-life were analyzed during six weeks. All CAS and PL treatments showed decreased weight loss compared to the regular atmosphere storage at the end of the storage. PL doses of 9 Jcm-2 showed less rot incidence, and PL doses of 6 Jcm-2 showed higher firmness compared to control; however, no significant difference (p < 0.05) has been iv observed in PL treated blueberries in all CAS in terms of firmness and rot incidence compared to control by week six. Increasing PL doses decreased antioxidant activity during storage time. Total soluble solids (TSS) and total acidity (TA) increased with increasing PL doses in the lower O2 concentration storage. Results showed that treating blueberries with PL doses of 6 and 9 Jcm-2 in CAS of 10kPa O2 and 8kPa CO2 provided the optimal conditions for maintaining the blueberries’ quality traits after four weeks. These findings can help increase the quality and shelf-life of blueberries, while minimizing their environmental impact, which could significantly impact the industry market, locally and globally. v Lay Summary Blueberries have been categorized as one of the top five main healthy foods noted by the United Nations Food and Agriculture Organization because of their high nutritional and health value. Blueberries are rich in phenolic acids, anthocyanins, and can help to prevent cancer, cardiovascular diseases, and inflammation. However, fresh blueberries are notoriously and qualitatively susceptible to post-harvest changes that affect the economy of the Canadian blueberry export industry. The objective of this study is to apply innovative non-thermal food processing technology (pulsed light) combined with controlled atmosphere storage to improve the post-harvest quality and shelf-life of blueberries. Results show that the combination of PL and CAS strategy effectively improved the blueberries’ quality and shelf-life. This finding will have important implications for the economy of the Canadian blueberry industry and growers by minimizing blueberry decays, and providing an innovative technology with a low environmental impact for extending the shelf-life of blueberries. vi Preface Research performed in Chapter 3 has been submitted for publication entitled: “Efficacy of Pulsed Light Fluences on the Post-harvest Quality and Shelf-life of Highbush Blueberries (cv. Draper)”. This research was designed and performed by Maryam Shojaei, under the supervision of Dr. Anubhav Pratap-Singh. vii Table of Contents Abstract .................................................................................................................................... iii Lay Summary ............................................................................................................................. v Preface ...................................................................................................................................... vi Table of Contents ..................................................................................................................... vii List of Tables ............................................................................................................................. ix List of Figures ........................................................................................................................... xi Acknowledgements .................................................................................................................. xiv Dedication ................................................................................................................................ xv Chapter 1: Literature review ...................................................................................................... 1 1.1. Blueberry Production ................................................................................................................. 1 1.2. Blueberry Structure .................................................................................................................... 2 1.3. Nutritional composition of Blueberries ...................................................................................... 2 1.4. Blueberry Shelf-life ..................................................................................................................... 4 1.5. Strategies to extend blueberry shelf-life ..................................................................................... 5 1.5.1 Controlled Atmosphere storage (CAS) .............................................................................................. 6 1.5.2 Modified Atmosphere Packaging (MAP) ........................................................................................... 8 1.6. Pulsed light .................................................................................................................................. 9 1.6.1. Effect of pulsed light on microorganism inactivation ......................................................................10 1.6.2. Effect of pulsed light on quality traits of fresh Produce ..................................................................14 1.6.3. Combination of PL with other methods ...........................................................................................15 Chapter 2: Hypothesis and objectives....................................................................................... 19 2.1. Research hypothesis .................................................................................................................. 19 2.2. Research objectives ................................................................................................................... 19 Chapter 3: Efficacy of Pulsed Light Fluences on the Post-Harvest Quality and Shelf-life of Highbush Blueberries (cv. Draper) .......................................................................................... 20 3.1. Introduction .............................................................................................................................. 20 3.2. Material and methods ............................................................................................................... 23 3.2.1. Sample collection and preparation ...................................................................................................23 3.2.2. Pulsed light treatments .....................................................................................................................23 3.2.3. Fruit quality assessment ...................................................................................................................24 3.2.4. Determination of antioxidant activity ..............................................................................................28 3.2.5. Statistical analyses ............................................................................................................................29 3.3. Results and discussion .............................................................................................................. 30 3.3.1. Weight loss ........................................................................................................................................30 3.3.2. Rot incidence ....................................................................................................................................31 3.3.3. Firmness ...........................................................................................................................................32 3.3.4. Color .................................................................................................................................................33 3.3.5. pH, titratable acidity, and total soluble solids ..................................................................................35 3.3.6. DPPH free radical scavenging activity .............................................................................................38 viii 3.4. Conclusion ................................................................................................................................. 39 Chapter 4: Investigating the quality and shelf-life of PL treated blueberries under CAS ........ 41 4.1. Introduction .............................................................................................................................. 41 4.2. Materials and methods ............................................................................................................. 43 4.2.1. Blueberry Samples ...........................................................................................................................43 4.2.2. Controlled Atmosphere Storage and Pulsed Light Treatments.......................................................45 4.2.3. Methods ............................................................................................................................................46 4.2.4. Design of Experiment .......................................................................................................................46 4.3. Results and Discussion: ............................................................................................................ 49 4.3.1. Color .................................................................................................................................................49 4.3.2. Rot incidence ....................................................................................................................................54 4.3.4. Total soluble solids (TSS) and titratable acidity (TA) .....................................................................63 4.3.5. DPPH free radical scavenging activity .............................................................................................69 4.4. Conclusion ................................................................................................................................. 73 Chapter 5: Conclusion and future directions ........................................................................... 75 5.1. Conclusions ............................................................................................................................... 75 5.2. Further Investigation ................................................................................................................ 76 Bibliography ............................................................................................................................. 77 ix List of Tables Table 1.1. Nutrient value of fresh blueberries per 100g ………………………………..…………3 Table 1.2. Selected published studies involving the impact of CAS on firmness and decay of blueberries ………………………………………………………………………………..…….....7 Table 1.3. Selected published studies involving the impact of PL on fruit, vegetables…………12 Table 1.4. Selected published studies involving the impact of PL on fruit juices………………...13 Table 1.5. Selected studies including the combination of PL with other strategies/technologies...16 Table 3.1. Impact of pulsed light on blueberry (cv. Draper) color during six-week storage at 0.5 °C and 90-95% RH………………………………………………………………..……………..34 Table 3.2. Impact of pulsed light on blueberry (cv. Draper) total soluble solid (TSS), pH, and titratable acidity (TA) during six-week storage at 0.5 °C and 90-95% RH………………………………………………………………………………………………..37 Table 4.1. Values of weight loss, firmness, DPPH free radical scavenging activity (IC50), total soluble solids (TSS), and titratable acidity (TA) of blueberries (cv. Draper) affected by pulsed light, storage time, O2 and CO2 concentrations at 0.5 °C and 90-95% RH….…………………..47 Table 4.2. Analysis of Variance (ANOVA) for the impact of pulsed light, storage time, O2 and CO2 concentrations on rot incidence of blueberries (cv. Draper) at 0.5 °C and 90%-95% RH………………………………………………………………………………………………..55 x Table 4.3. Analysis of Variance (ANOVA) for the impact of pulsed light, storage time, O2 and CO2 concentrations on weight loss and firmness of blueberries (cv. Draper) at 0.5 °C and 90-95% RH………………………………………………………………………………………..………59 Table 4.4. Analysis of Variance (ANOVA) for the impact of pulsed light, storage time, O2 and CO2 concentrations on titratable acidity (TA) and total soluble solids (TSS) of blueberries (cv. Draper) at 0.5 °C and 90-95% RH………………………………………………………………..64 Table 4.5. Analysis of Variance (ANOVA) for the impact of pulsed light, storage time, O2 and CO2 concentrations on DPPH free radical scavenging activity of blueberries (cv. Draper) at 0.5 °C and 90-95% RH ……………………………………………………...…………………………..69 xi List of Figures Figure 1.1. Pulsed light treatment for food processing………………………………………….10 Figure 3.1. Pulsed light processing of blueberries (cv. Draper)……….…………………….….25 Figure 3.2. Impact of pulsed light treatments on weight loss in blueberries (cv. Draper) during six-week storage at 0.5 °C and 90-95% RH…………………………………………………..………31 Figure 3.3. Impact of pulsed light on firmness in blueberries (cv. Draper) during six-week storage at 0.5 °C and 90-95% RH…………………………………………………………………………32 Figure 3.4. Impact of pulsed light on antioxidant activity in blueberries (cv. Draper) during six-week storage at 0.5 °C and 90-95% RH………………………………………………..…………33 Figure 4.1. Pulsed light processing of blueberries (cv. Draper) maintained in controlled atmosphere storages………………………………………………………...……………………44 Figure 4.2. Effect of pulsed light (A), time of storage (B), O2 concentration (C), and CO2 concentration (D) on lightness (L*) of highbush blueberries (cv. Draper), where A, C, D are at the center point of the design and B is at week 6……………………………………………………..51 Figure 4.3. Effect of pulsed light (A), time of storage (B), O2 concentration (C), and CO2 concentration (D) on blueness (b*) of highbush blueberries, where A, C, D are at the center point of the design and B is at week 6………………………...………………………………...………53 xii Figure 4.4. (a) Response surface of the blueness of highbush blueberries (cv. Draper) affected by CO2 concentration and pulsed light, (b) Response surface of the redness (a*) of highbush blueberries (cv. Draper) affected by CO2 concentration and O2 concentration..……………………………………………………………………………………54 Figure 4.5. Effect of pulsed light (A), time of storage (B), O2 concentration (C), and CO2 concentration (D) on rot incidence of highbush blueberries, where A, C, D are at the center point of the design and B is at week 6…………………………………………...………………...……57 Figure 4.6. Response surface of rot incidence of highbush blueberries (cv. Draper) during 6 weeks as affected by (a) time of storage and pulsed light, (b) O2 concentration and time of storage, (c) CO2 concentration and time of storage, (d) CO2 concentration and O2 concentration…………….58 Figure 4.7. Response surface of weight loss of highbush blueberries (cv. Draper) affected by (a) time of storage and pulsed light, (b) O2 concentration and pulsed light, (c) O2 concentration and pulsed light, (d) CO2 concentration and time of storage, (e) CO2 concentration and time of storage, (f) CO2 concentration and O2 concentration……………………..……………………………….61 Figure 4.8. Response surface of firmness of highbush blueberries (cv. Draper) affected by (a) CO2 concentration and pulsed light, (b) CO2 concentration and time of storage……………………….63 Figure 4.9. Response surface of total soluble solids of highbush (TSS) blueberries (cv. Draper) affected by (a) time of storage and pulsed light, (b) O2 concentration and pulsed light, (c) O2 concentration and pulsed light, (d) CO2 concentration and time of storage, (e) CO2 concentration and time of storage, (f) CO2 concentration and O2 concentration…………………………………66 xiii Figure 4.10. Response surface of total acidity of highbush blueberries (cv. Draper) during six-weeks affected by (a) time of storage and pulsed light, (b) O2 concentration and pulsed light, (c) CO2 concentration and pulsed light, (d) O2 concentration and time of storage, (e) CO2 concentration and time of storage, (f) CO2 concentration and O2 concentration……………………………………………………………………………………..68 Figure 4.11. Effect of pulsed light (A), time of storage (B), O2 concentration (C), and CO2 concentration (D) on antioxidant activity of highbush blueberries (cv. Draper) where A, C, D are at the center point of the design and B is at week 6………………………………………………..71 Figure 4.12. Response surface of antioxidant activity of highbush blueberries (cv. Draper) by plotting; (a) pulsed light and time of storage, (b) O2 concentration and pulsed light, (c) CO2 concentration and pulsed light, (d) O2 concentration and time of storage, (e) CO2 concentration and time of storage, (f) CO2 concentration and O2 concentration…………………………………72 xiv Acknowledgements I would like to express my sincere gratitude to my supervisor, Dr. Anubhav Pratap-Singh, for providing me with the opportunity to pursue my graduate studies in his laboratory, for his unwavering support, and his outstanding mentorship throughout my educational journey. I am also deeply indebted to my supervising committee, Dr. David D. Kitts and Dr. Simone Diego Castellarin, for their insightful input and support, which significantly helped strengthen my research. I would also like to thank Dr. Farahnaz Fathordoobady, Dr. Azita Madadi Noei, Dr. Anika Singh, and Dr. Ismaeil Fazel for their support and encouragement throughout my studies. My special thanks also go to Peter Hoffman for all the technical support he has given me all along. I also wish to thank all laboratory members of the Food Process Engineering laboratory and the Wine Research Centre who have always supported and cheered me up. I am eternally grateful to my beloved parents, my sister and brother, who inspired me to pursue my dreams. Finally, I am immensely thankful to my husband and my kind-hearted son for their kindness, unconditional support, and for always being there for me. xv Dedication This work is dedicated to my husband, who has been a constant source of support and encouragement throughout the graduate school and life, and to my son for the hope, love, and joy he has brought to my life. 1 Chapter 1: Literature review 1.1. Blueberry Production Highbush blueberries, Vaccinium corymbosum L., are indigenous to North America (Bratsch & Pattison, 2009). In addition, there are other commercially important Vaccinium crops such as V. angustifolium known as lowbush blueberries and V. ashei, known as rabbiteye blueberries. Highbush blueberries are produced widely in the US and different areas worldwide, and the most commercial cultivars are Bluecrop, Blueray, Jersey, and Duke (Retamales, 2012). In 2016, Canada was the third-largest exporter of highbush blueberries in the world, and British Columbia (B.C.) was the largest highbush blueberry-producing regions in the world (Agriculture and Agri-Food Canada, 2016). In terms of marketed production and value, blueberries were considered as the most important fruit crop in 2019 in Canada (Statistical overview of the Canadian fruit industry, 2019). In addition, blueberries remained the top fruit export by volume and value in Canada, and B.C. exports the vast majority of highbush blueberry varieties in Canada (Agriculture and Agri-Food Canada, 2021). Over the past decade, there has been an increase in demand for blueberries because of their rich nutritional and medicinal value. Blueberries contain vitamins A and C, dietary fiber, and magnesium. Studies have also shown that the antioxidants in Blueberries can help minimize risk of cancer and heart disease (Skrovankova et al., 2015; Gonzalez-Villagra et al., 2020). 2 1.2. Blueberry Structure Blueberries are simple fruit with a fleshy pericarp. This fleshy fruit develops from the ovary of one flower by increasing cell division and cell expansion. The pericarp is made up of an exocarp (skin) and a mesocarp (pulp or flesh). The skin consists of the epidermis and hypodermis (Moggia et al., 2017). Blueberry fruit’s epidermis is covered by a waxy cuticle which serves as a protective barrier against moisture loss, pathogens, and mechanical damages after harvesting (Case, 2019). Chu et. al. (2017) reported triterpenoids and β-diketones constituted the main wax composition of blueberries. The structure of the cuticle showed a major effect on the transpiration in the fruit, which, in turn, significantly impacted on bioactive compounds such as anthocyanins located underneath the epidermis (Michalska & Lysiak, 2015). The hypodermis has a high level of anthocyanin in the skin, which is typically responsible for the blue color of blueberries (Case, 2019). 1.3. Nutritional composition of Blueberries The principal compositions of fresh blueberries particularly consist of 84% water, 9.7% carbohydrates, 0.6% protein and 0.4% fat (Michalska & Lysiak, 2015). In ripe blueberries, glucose and fructose are found to be the predominant sugars with the equal quantities. The major organic acid in blueberries are citric, malic, quinic and chlorogenic acids, with citric acid being the most predominant one (Paniagua 3 Gonzalez, 2012). They are known to be a rich source of vitamin C containing 10 mg of ascorbic acid per 100 g of fresh blueberries (Michalska & Lysiak, 2015). In addition, they are known as an excellent source of bioactive compounds mainly polyphenols including anthocyanins, procyanidins and chlorogenic acid (Paniagua Gonzalez, 2012). Table 1.1 illustrates the nutrient value of fresh blueberries per 100g (USDA, 2019). Table 1.1. Nutrient value of fresh blueberries per 100g Fresh blueberries (per 100g) Value Energy 57Kcal Water 84.2g Dietary fiber 2.4g Protein 0.74g Fat 0.33g Ash 0.24g Carbohydrate 14.5g Glucose 4.88g Fructose 4.97g Sucrose 0.11g Starch 0.03g Potassium 77mg Magnesium 6mg Phosphorus 12mg Vitamin C 9.7mg Vitamin K 19.3µg Vitamin A 54IU IU: International unit 4 1.4. Blueberry Shelf-life Blueberries are highly perishable due to water loss and microbial growth. The blueberry shelf-life varies between two (highbush blueberries) to four weeks (lowbush blueberries), and is normally affected by factors such as type of cultivars, fruit ripeness stage, harvest method, existence of fruit disease, and condition of storage (relative humidity, temperature, and atmosphere conditions) (Hancock et al., 2008). Ripening blueberries undergo a number of physiochemical and structural alterations after harvest, which result in the breakdown of complex carbohydrates into sugar, color changes, firmness and acidity decreases (Garcia-Gomez et al., 2021). The major quality parameters that impact on purchase behaviors of customers are appearance, aroma/flavor and texture (Gallagher et al., 2011). In addition, mechanical damages during berries’ harvest, transportation or storage is a crucial factor that can increase the risk of infection leading to decrease the post-harvest life of the blueberries. The most common pathogens cause decay in blueberries are Botrytis cinerea, Alternaria sp., followed by Colletotrichum sp., Fusarium, and Penicillium (Paniagua Gonzalez, 2012). Moreover, cold temperature with high relative humidity is the major factor which can decrease the water loss, leading to increased turgidity and reduced wilting (Wills et al., 2007). 5 1.5. Strategies to extend blueberry shelf-life Many strategies have been tested to extend blueberry shelf-life. Some of the most important techniques include cold storage, maintaining the storage conditions under proper humidity, controlled temperatures, chlorine dioxide gas treatment, controlled atmosphere storage (CAS), modified atmosphere packaging (MAP), and non-thermal processing techniques (Duan et al., 2011; Concha-Meyer, 2013; Wang et al., 2019). Cold storage decreases microbial growth. In addition, the respiration rate decreases significantly, which causes a natural senescence delay. A suitable relative humidity can help maintain water content by slowing down the moisture transition, which is the water vapor pressure difference between fruit surfaces and the atmosphere (Tano et al., 2005). In order to decrease weight loss and firmness of the blueberries, it is suggested that the storage condition of blueberries be maintained at 0.5°C with relative humidity (RH) of 90-95% (Perkins-Veazie, 2016). Chlorine dioxide (ClO2) gas treatment has been used as a disinfectant in fruit and vegetables, and it has been reported to be able to decrease the blueberries’ decay noticeably and increase their shelf-life (Sun et al., 2014); however, as a chemical disinfectant, it has some disadvantages including being extremely unstable substance, toxic to humans, and to the environment (Concha-Meyer, 2013). Regarding the controlled atmosphere storage (CAS), CO2 enrichment and O2 reduction, can decrease fruit respiration rate and extend the shelf-life of the 6 blueberries. In addition, modified atmosphere packaging (MAP) method helps prolong shelf-life due to decrease in respiration rate of the fruits (Paulsen et al., 2019). While controlled atmosphere storage (CAS) has to be monitored carefully to maintain the proper concentration of gases, the gaseous composition in modified atmosphere packaging (MAP) continuously changes because of chemical reactions and microbial activity (Mullan & McDowell, 2003). Regarding the non-thermal processing technologies such as high-pressure processing (Tadapaneni et al., 2014), UV-C irradiations (Perkins-Veazie, 2008; González-Villagra et al., 2020), and ultrasound (Aday et al., 2013), previous studies showed some significant effects on the fungal decay reduction and reported that the quality parameters and nutritional values of treated fruits did not necessary change which resulted in prolonging their shelf-life. 1.5.1 Controlled Atmosphere storage (CAS) Controlled atmosphere storage (CAS) refers to the post-harvest storage technology in which the gaseous composition of the storage is adjusted to enhance the quality and shelf-life of perishable vegetables and fruit. In combination with proper refrigerated conditions, CAS can prolong the storage life of many perishable products using in storage and to enable export via sea freight worldwide (Wills et al., 2007; Ma et al., 2019). CAS is used commercially for exporting fresh blueberries by sea freight shipment and it may also be used, on a small scale, by in-land storage 7 facilities that improve the berry shelf-life. High CO2 concentration eliminates decay growth in the CAS of blueberry storage, while the impact of CAS on ripening attributes is less important on the quality of blueberry since they are picked at full ripening, and they don’t respond to the application of ethylene (Alsmairat et al., 2011). However, studies indicate increased CO2 concentrations and lower O2 can cause physiological damage in blueberries leading to softening (Schotsmans et al., 2007; Matityahu et al., 2016) and off-flavour development (Harb and Streif, 2004, Krupa and Tomala, 2007) constituting a significant risk to the export industry. The recommended CAS for the blueberries is 8% to 15% of CO2 and above 1% O2 concentration to prevent fermentation damage. In addition, some research shows that O2 concentrations between 1% and 10% can help prevent further decay (Paniagua et al., 2014). Therefore, further evaluations of O2 influence on blueberry quality are still required to improve the use of CAS in blueberries. Table 1.2 shows the effect of CAS on the blueberries’ firmness and decay, according to some published studies. Table 1.2. Selected published studies involving the impact of CAS on firmness and decay of blueberries CO2 level (kPa) O2 level (kPa) Storage time (Week) Firmness Decay (%) Cultivar References 0 5 10 15 2 2 2 2 5 *MTG Index 498 369 344 42.3 17.5 11.6 Highbush blueberries Fen et al., 1993 8 351 11.1 0 6 12 18 24 20.9 18 18 18 18 7 Compression (g) 160 183 141 110 95 8.5 6.6 2.5 4 4.3 Duke Highbush blueberries Harb & Streif, 2004 0 6 12 18 24 20.9 18 18 18 18 7 Compression (g) 180 175 155 110 85 35 33 15 1 0.5 Bluecrop Highbush blueberries Harb & Streif, 2004 0 15 20.9 2.5 4 Compression (N) 3.5 2.8 - Rabbitrye blueberries Schotsmans et al., 2007 0.5 10 10 20.9 20 2.5 6 Compression (N) 1.54 1.62 1.60 3.53 1.39 0.44 Highbush blueberries Paniagua et al., 2014 0.5 10 20.9 5 6 Average loss of initial firmness (%) 40 29 11 3 Duke Highbush blueberries Falagan et al., 2020 *Momentum Transfer Generation (MTS) 1.5.2 Modified Atmosphere Packaging (MAP) Modified Atmosphere packaging (MAP) is a packaging technology in which the internal atmosphere of the package is modified to improve the shelf-life of the product. There are two types of MAP; Passive and active MAP. In passive MAP, 9 stemming from gas permeability and respiration rate associated with the packaging film results in a steady state condition after a long period of time. In the case of active MAP, deployment of a scavenging system or flushing of gases in the package serves to induce acceleration of gas composition modification which precludes exposing the product to highly-concentrated gasses (with potentially damaging effects) (Charles et al., 2008). Modified atmosphere packaging limits gas exchange which leads to increased level of CO2 and O2 reduction (Waghmare et al., 2018). Different factors including the weight of the product, the temperature of the storage, the fruit respiration rate, the cultivar and the stage of ripening can impact on the final composition of gases. In addition, the concentration gradient between inside and outside of the atmosphere of the package, the package and permeability can affect the exchange of gases between the inside and outside of the atmosphere in the package (Briano et al., 2015). It has been reported that MAP at 0°C could enhance the firmness of highbush blueberries compared to the control treatment (Moggia et al., 2014). Additionally, Koort et al. (2018) demonstrated the shelf-life of half-highbush and lowbush blueberries in MAP (Xtend blueberry bag) was prolonged by 9 and 15 days respectively compared to regular atmosphere storage. 1.6. Pulsed light Pulsed light (PL) is an emerging non-thermal technology wherein high-intensity and short-duration wide spectrum (200-1100nm) light pulses are employed for 10 decontamination of food (Manal et al, 2020). It is well-documented that PL has a great potential to inactivate microorganisms, including fungal spores, bacteria, yeast, and viruses (Gomez-Lopez et al., 2005, Oms-Oliu et al., 2010, Wiktor et al., 2019). In 1996, PL was approved by the U.S. Food and Drug Administration (FDA) as a food processing technology for decontamination of food and packaging surfaces. They recommended using PL with a xenon lamp having the emission wavelength ranges from 200 and 1100 nm with a maximum cumulative dose of 12 J cm-2 (Mandal et al., 2020). The electromagnetic spectrum of pulsed light includes UV radiation (200–400 nm; UV-C: 200–280 nm, UV-B: 280–315 nm, UV-A: 315–400 nm), visible light (400–700 nm), and infrared radiation (700–1100 nm) (Bhavya & Umesh Hebbar, 2017). Figure 1.1. Pulsed light treatment for food processing 1.6.1. Effect of pulsed light on microorganism inactivation The mechanism of microbial inactivation is explained in terms of photo-chemical, and photo-thermal effects of PL. The major disinfection effect of PL is reported to be related to photo-chemical effect of PL. The germicidal effect of PL is attributed to UV absorption of DNA molecules and UV- C accounts for the half the 11 germicidal effect (Cao, 2017). The germicidal effect of PL on microbial DNA is mainly due to pyrimidine dimer formation in the DNA (Pollock et al., 2017). The ultra-violet (UV) fraction of the PL spectrum is associated with microbial inactivation, as well as other chemical changes in food products. A photo-thermal mechanism of PL has also been claimed to account for microbial inactivation which is caused by IR region of PL spectrum (Mandal et al., 2020). Previous research has found that regional overheating by high intensity of light pulses could lead to damage to cell membrane and cell disruption (Cao, 2017). Also, Nicorescu et al. (2013) indicated that the cell wall disruption happened in Bacillus subtilis due to the photo-thermal stress of PL treatment. Wekhof et al. (2001) found that deformation of cell was seen in Aspergillus niger after treating by PL, however, UV-C did not cause any cell wall damages. There are some factors that can restrict the efficacy of PL microbial inactivation on food production including the composition and opacity of food, and the possibility of shadowing effect of upper level of inactivated microorganism for the lower layers of microorganism in the food (Gomez-Lopez et al., 2005). In Table 1.3 and Table 1.4, the results of some published studies involving PL inactivation of microorganisms on fruits, vegetables, and fruit juices are summarized. 12 Table 1.3. Selected published studies involving the impact of PL on fruit, vegetables Food products (Fruits and vegetables) Microorganisms Pulse energy (J cm-2) Log reduction (CFU/g) References Strawberry Murine norovirus Escherichia coli O157:H7 Salmonella 22.5 0.9, 1.9, 2.1 respectively Huang et.al. 2017 Blueberry 3.8, 5.7, 4.2 respectively Strawberry E. coli O157:H7 Salmonella Murine norovirus 1.27 3.3, 2.8, 1.8 respectively Huang et.al. 2015 Raspberry 5.3, 4.9, 3.6 respectively Blueberry Salmonella E. coli O157:H7 56.1 3.6 (calyx), >5.9 (skin) 3.0 (calyx), >5.8 (skin) and respectively John& Ramaswamy, 2018 Raspberry Salmonella E. coli O157:H7 28.2 4.5, 3.9 respectively Xu & Wu, 2016 Tomatoes Saccharomyces cerevisiae 2.2 23 Aguiló-Aguayo et al., 2013 Spinach E. coli Listeria innocua 0.8 1.72, 1.85 respectively Aguero et al., 2016 Endive salad E. coli L. innocua 1 2.34, 2.54 respectively Kramer et al., 2015 Mung bean sprouts 1.91, 1.55 respectively Tomatoes E. coli L. innocua 16 1.4, 0.9 respectively Valdivia-Najar et al., 2017 Tomatoes, cauliflowers, plums, sweet peppers Bacillus cereus 5.4 1.3-1.8 Luksiene et al., 2012 Fresh-cut avocado E. coli L. innocua 0.4 3.33, 2.97 respectively Ramos-Villarroel et al., 2011 Fresh-cut mushroom E. coli L. innocua 12 3, 2 respectively Ramos-Villarroel et al., 2013 13 Fresh-cut watermelons E. coli L. innocua >3, 2.79 respectively Ramos-Villarroel et al., 2012 Tomato stem scar Salmonella enterica 31.5 2.3 Leng et al., 2020 Strawberries Salmonella 3 0.8 Cao et al., 2019 Table 1.4. Selected published studies involving the impact of PL on fruit juices Food products (Fruit juice) Microorganisms Pulse energy (J cm-2) Log reduction (CFU/g) References Apple juice Penicillium expansum 32 3.76 Maftei et al., 2014 Apple juice Alicyclobacillus acidoterrestris 71.6 3.0-3.5 Ferrario & Guerrero, 2017 Apple juice E. coli ATCC 2592 8.8 7.29 Sauer & Moraru, 2009 Apple juice E. coli O157:H7 5.1 3.9 Caminiti et al., 2011 Apple juice Lactobacillus brevis 17.5 3 Ignat et al., 2014 Apple juice E. coli L. innocua 28 4.7, 1.93 respectively Palgan et al., 2011 Orange juice 1, 1 respectively Orange juice E. coli 5.1 2.42 Munoz et al., 2011 Orange juice L. innocua E. coli S. enteritidis, S. cerevisiae 71.6 0.3–0.8 for all of strains Ferrario et al., 2015 Apple juice 1.6, 2.1, 2.4, 1 respectively Strawberry juice 0.3–0.8 for all of strains 14 Melon juice L. innocua E. coli S. enteritidis, S. cerevisiae 71.6 6, 6, 5, 7 respectively Ferrario et al., 2013 Orange juice Pseudomonas aeruginosa 29.21 0.5-2 Hwang et al., 2015 Grape juice 1.6.2. Effect of pulsed light on quality traits of fresh Produce The quality traits of fresh vegetables and fruits treated by PL showed various results and were generally analyzed by modifications in color, texture, physicochemical parameters and sensory attributes (Kramer et al., 2017, Rowan, 2019). Schreiner et al. 2014 reported that UV-B irradiation is one of the major factors responsible for the formation of secondary plant metabolites as carotenoids, phenolic compounds, and glucosinolates. This can be associated with some studies reporting the enhancement of the formation of nutritional compounds in fresh produce after PL treatment (Kramer et al., 2017). In this regard, Pataro et al. (2015) indicated that nutritional value of PL treated green tomatoes increased with the growing formation of total phenolic compounds, lycopene, and total carotenoid compounds. Also, Anugu (2013) reported that total anthocyanins and flavonoids in blueberry wine increased after PL treatment. Bialka and Demirci (2007, 2008) reported no significant changes in color and sensory attributes of blueberries, raspberries, and strawberries treated by PL compared to the untreated samples. Anugu (2013) found no significant changes in lightness values and hue of the blueberry wine using PL 15 treatment. However, Ramos-Villarroel et al. (2011, 2012a, 2012b) showed that there was a significant decrease in lightness value and firmness of mushrooms, watermelons and avocados. Valdivia-Najar et al. (2017) observed a slight increase in titratable acidity and slight decrease in total soluble solid and pH in tomatoes treated by PL of 8 J cm-2 during 20 days of storage period. However, Palgan et al. (2011) did not report any significant changes in total soluble solid and pH of PL-treated apple juice. Regarding the physicochemical properties, variation in the results observed in different studies can be due to product matrices (Mandal et al., 2020). Deterioration of quality tends to mostly occur during storage, not immediately following exposure to PL. As such, experiments involving application of PL to products can have implications not only for microbial reductions but also for extension of shelf-life. Since the effect of PL on quality traits of different products is likely to vary with dose, it is paramount to seek process parameters that can guarantee a gentle effective treatment resulting in significant microbial inactivation (Kramer et. al., 2017). 1.6.3. Combination of PL with other methods Due to limitations in the application of PL for the fresh produce (i.e. sample heating, browning, shadowing effect, and uneven surfaces), PL treatment is often combined with other strategies. Combined methods have been mainly developed to 16 minimize the processing limits and improve the processing effect to preserve the quality attributes of foods (Bhavya & Umesh Hebbar, 2017). Application of PL in combination with anti-browning compounds has been showed to successfully improve quality and shelf-life of fruits and vegetables. Gomez et. al. (2012) found that applying the solution of ascorbic acid/calcium chloride on apples could reduce the browning before PL treatment. Moreover, fresh-cut apples coated with pectin treated by PL showed less microbial growth during the storage time than PL alone (Moreira et. al., 2017). It has also been reported that integrated effects of PL (12 J cm-2) and malic acid (MA) significantly reduced Escherichia coli and Listeria innocua growth compared to PL or MA alone (Bhavya & Umesh Hebbar, 2017). Huang et. al. (2015) indicated that treated raspberries and blueberries by combination of wet PL and 1% H202 could reduce 5.6 log CFU/g of Salmonella. However, the combination of PL (30 µs, 15 Hz, 40–250 s) with UV-C on strawberries during 10 days of storage at 12 ºC exhibited no decrease in development of Botrytis cinerea rather than applying PL alone (Gomez et. al., 2011). Selected studies including the combination of PL with other strategies/technologies are illustrated in Table 1.5. Table 1.5. Selected studies including the combination of PL with other strategies/technologies Food product Combination of PL treatment with Main results References 17 Blueberries, Raspberries Water assisted PL and H2o2 Blueberries: reduced Salmonella >5.6 log CFU/g Raspberries: reduced Salmonella 4 log CFU/g Huang et al., 2015 Green beans Chitosan-based coating with nano-emulsion of essential oil of mandarin No significant effect on L. innocua Donsi et al., 2015 Fresh-cut apple Pectin coating and ascorbic acid /calcium chloride solution Reducing browning, maintaining antioxidant activity, no effect on microbial population and Moreira et al., 2017 Strawberries Mild thermal treatment (40 or 45◦C, 3 or 15 min) A two-day delay of Botrytis cinerea spoilage Gomez et. al., 2011 Fresh-cut watermelon, avocado and mushroom Malic acid solution > 5 log reduction of L. innocua and E. coli compared to individual PL or MA treatment Ramos-Villarroel et al., 2015 Fresh-cut mango Alginate coating and Malic acid solution Additively reduced 3.9 log of L. innocua Salinas-Roca et al., 2016 RTE sausages Nisin treatment More significant reduction of L. innocua (4.03 log CFU) than PL alone (1.37 log CFU) or nisin alone (2.35 log CFU) Uesugi and Moraru, 2009 Apple juice Ultrasound 6 log reduction in yeast Ferrario et al., 2015 Apple juice Thermo-sonication Higher inactivation effect on E. coli than any other treatment individually Munoz et al., 2012 Attempts to inactivate several microorganisms through the combined effect of PL and other methods are well documented. Hence, to consider quality and shelf-life of fresh blueberries as well as their safety, it is necessary to consider other possible technologies in combination with PL which can promote blueberry quality 18 traits and shelf-life. With the growing demand for environmentally friendly processing, the use of PL can be a potential alternative to chemical disinfection of the blueberries such as chlorine; however, in order to minimize PL limitations, combination of PL with CAS to enhance the safety and shelf-life of blueberries has not been evaluated yet. Findings will have significant implications for exporting blueberries to overseas markets. 19 Chapter 2: Hypothesis and objectives This study aimed to evaluate dose tolerance of fresh blueberries to PL and effect of combination of PL with CAS on fruit quality parameters (i.e. color, texture, rot incidence, and weight loss), antioxidant activity, physicochemical attributes (pH, titratable acidity [TA], and total soluble solids [TSS]), and shelf-life at 0.5°C during a period of six weeks (a common time frame for blueberries to be exported to international markets). 2.1. Research hypothesis Optimizing pulsed light as an emerging non-thermal food processing technology combined with controlled atmosphere storage can improve post-harvest quality, nutritive value, and shelf-life of highbush blueberries (cv. Draper) grown in BC. 2.2. Research objectives • To investigate the effect of PL treatment to enhance the post-harvest life of blueberries • To investigate the quality and shelf life of PL treated blueberries under CAS 20 Chapter 3: Efficacy of Pulsed Light Fluences on the Post-Harvest Quality and Shelf-life of Highbush Blueberries (cv. Draper) 3.1. Introduction Blueberries (Vaccinium spp.) have been recognized by the Food and Agriculture Organization of the United Nations as one of the five main healthy foods because of their high nutritional and health values (Wang et al. 2017). Blueberries are known to contain vitamins A and C, dietary fibre, and magnesium. They also possess substantial amounts of bioactive phenolic compounds, especially anthocyanins and flavanols, which help prevent cancer, cardiovascular diseases, and inflammation (Skrovankova et al., 2015). Blueberries are widely cultivated in North America, being the second most important fruit in Canada in 2019 based on marketed production (Agriculture and Agri-Food Canada, 2020). In fact, blueberries are the top exported fruit by value and volume in Canada, with the largest proportion being highbush cultivars (USDA foreign agricultural service, 2017). However, fresh blueberries are very susceptible during post-harvest storage due to water loss and mold decomposition (Chea et al., 2019), which would cause great loss in their economic value. Blueberry quality is normally affected by factors such as ripening, harvest date, growing conditions, and post-harvest storage (including relative humidity, temperature, and atmosphere conditions) (Hancock et al., 2008; Liu, 2019). Fruit 21 appearance, flavor, and texture are the major quality traits that affect the consumers’ choices (Gallagher et al., 2011; Cao, 2017). Consequently, the preservation of fruit appearance, texture, and flavor during storage is essential to meet the consumer satisfaction. Conventional strategies have been employed to maintain blueberry quality and extend their shelf-life, including the storage conditions under proper humidity, controlled temperatures, and atmosphere compositions. Elevated RH could efficiently slow down the moisture loss and help maintain the water content in fruits (Tano et al., 2005; Cao, 2017). It is recommended to store blueberries at 0.5°C and 90-95% RH (Perkins-Veazie, 2016). Over the past decade, due to an increased demand for fresh and minimally processed food, novel techniques have been developed for food storage and processing. Pulsed light (PL) treatment is an innovative non-thermal food processing technology which uses intense and short-time light pulses with a broad spectrum (200-1100 nm), including ultraviolet, visible light, and infrared light (Elmnasser et al., 2007; Palgan et al., 2011; Bhavya and Hebbar, 2017; Mandal et al., 2020; Mandal and Pratap-Singh, 2021). PL has been demonstrated to obtain a great potential to inactivate microbial spoilage caused by fungi, bacteria, and yeasts in horticultural products such as strawberries (Marquenie et al., 2003), spinach and bell pepper (Gomez-Lopez et al., 2005), as well as raspberries (Bialka & Demirci, 2007), which 22 can improve safety of fruits with prolonged shelf-life. In this context, Huang et al. (2017) noticed that blueberries were more likely to be decontaminated by PL than strawberries due to their smoother skin. Bialka and Demirci (2007) treated blueberries, raspberries, and strawberries using UV light and observed no color and sensory changes, as well as no damages on the treated samples as compared to the untreated ones. However, effect of PL on fruit quality changes during long-term post-harvest storage of blueberries have not been extensively studied yet. Since the demand for consumption of fresh blueberries is speeding up, the extension of shelf life could potentially boost the blueberry economy by minimizing the blueberry quality deterioration and prolonging their shelf-life. The objective of the present study was to evaluate the impact of different PL doses on fruit quality and shelf-life in highbush blueberries. Basic fruit quality parameters (i.e. color, texture, rot incidence, and weight loss), antioxidant activity, physicochemical attributes (pH, titratable acidity [TA], and total soluble solids [TSS]), and shelf-life were assessed during a period of six weeks, considering the common time needed for blueberries to enter international markets. 23 3.2. Material and methods 3.2.1. Sample collection and preparation Fresh highbush blueberries (cv. Draper) were supplied by British Columbia Blueberry Council (Abbotsford, BC, Canada). They were hand-harvested at commercial maturity from a local blueberry farm located in Fraser Valley (Abbotsford, BC, Canada) in mid-August of 2020 and transferred to the laboratory within 3 hours at 4 °C. After eliminating overripe (soft), under ripe (poor color), and defected fruits, twenty blueberries with similar size and color were picked for each clamshell (4.4 oz, 130.12 mL). For each treatment, three clamshells of blueberries (n=20) were assessed at week 0, 2, 4, and 6 of the storage time. 3.2.2. Pulsed light treatments All experiments were performed using a bench-top pulsed light equipment at the Food Process Engineering Laboratory, Faculty of Land and Food Systems (The University of British Columbia, Vancouver BC), indigenously designed in collaboration with Solaris Disinfection Inc. (Mississauga, ON, Canada). The equipment used a cylindrical xenon lamp emitting 200-1100 nm broad spectrum light pulses. The energy profile of lamp was symmetrical along its length with the energy values being maximum at the centre of the lamp. For PL treatments, berries from each biological replicate were taken out from the clamshell and placed on a 24 clear glass petri dish with high light transmissivity. The petri dish was centered over the lamp housing at 5 cm from the lamp for all treatments. Energy dose per pulse at 5 cm distances was measured as per the methodology of Mandal and Pratap-Singh (2021) by using a pyroelectric head sensor (PE80BF-DIF-C, Ophir-Spiricon LLC, UT, United states) with the value of 27.17 ± 0.38 mJ cm-2 per pulse. The samples were exposed to PL at the frequency of 5 Hz for three different duration to impart three different PL doses: 3 J cm-2 (22 s), 6 J cm-2 (44 s), and 9 J cm-2 (66 s). An aluminium reflector was placed over the lamp housing to reflect the light back to samples. A schematic diagram of PL treatment of samples is given in Figure 3.1. Blueberry samples without any PL treatments were considered as control treatment (CONTROL). 3.2.3. Fruit quality assessment All samples were stored at 0.5°C and 90-95% RH for six weeks in a refrigerator (Hoshizaki, B & G Refrigeration, FL, USA). Basic fruit quality parameters (i.e. color, texture, rot incidence, and weight loss) were assessed using fresh berries at harvest (week 0) and during post-harvest storage on a bi-weekly basis (i.e. two weeks after storage [week 2], four weeks after storage [Week 4], and six weeks after storage [week 6]), while the berries for antioxidant capacity and physicochemical attributes 25 (pH, TA, and TSS) were taken out from the refrigerator at the same stage and were stored at -80°C until further analyses. Figure 3.1. Pulsed light processing of highbush blueberries (cv. Draper) 3.2.3.1. Weight loss Fruit weight was recorded by each replicate using a digital balance (Sartorius, Germany) with the accuracy of 0.01g. The percentage of weight loss per initial blueberry weight was determined as in Equation 3.1. 𝑊𝑒𝑖𝑔ℎ𝑡 𝑙𝑜𝑠𝑠 (%) = 𝑤0 − 𝑤2𝑤0 ∗ 100 (𝐄𝐪.𝟑. 𝟏) 3.2.3.2. Rot incidence Berries with the symptoms of decay such as fungal mycelium, shrinkage or soft were removed from the clamshells and weighed at each stage. Rot incidence was 26 calculated by the percentage of decayed berry weight to total berry weight (Equation 3.2). 𝑅𝑜𝑡 𝐼𝑛𝑐𝑖𝑑𝑒𝑛𝑐𝑒 (%) = 𝑅𝑜𝑡𝑡𝑒𝑛 𝑏𝑒𝑟𝑟𝑦 𝑤𝑒𝑖𝑔ℎ𝑡𝑇𝑜𝑡𝑎𝑙 𝑏𝑒𝑟𝑟𝑦 𝑤𝑒𝑖𝑔ℎ𝑡 ∗ 100 (𝐄𝐪. 𝟑. 𝟐) 3.2.3.3. Texture analysis Fruit firmness (g) was evaluated in individual berries, using a TA.XT Plus Texture Analyzer (Texture Technologies Corp., NY, USA). Six berries were randomly selected from each replicate. Each berry was subjected to a double compression with a wait between two cycles which imitated two bites eating by humans. The maximum force that the blueberry withstands on the first compression is considered as firmness. As per Doving et al. (2005), the probe height was calibrated to 13 mm above the TA-90 base platform so that the blueberry could be aligned directly under the probe. The probes were cleaned by a delicate wiper after the analysis of each berry to remove any adhered material. Fruit penetration was set at 3 mm. The following test settings were used: Measure Force in Compression; Return to Start; pre-test speed of 2 mms-1 and test speeds of 1 mms-1 with an automatic trigger set to 5 grams of force; test distance of 3 mm into the blueberries; and a post-test withdrawal speed of 2 mms-1. 3.2.3.4. Color determination 27 Color parameters were determined using a Hunter Lab colorimeter (Hunter Lab Inc., Reston, VA, USA). CIELAB color scale was selected to study the following parameters: L* = 0-100 (black to white), −a* (greenness) to +a* (redness), −b* (blueness) to +b* (yellowness), and total color difference (DE) was calculated according to the Equation 3.3, where L*control, a*control and b*control were color value at day 0. Each sample was measured at four different positions and five berries were randomly picked from each replicate. Values were expressed as mean ± standard deviation (SD, n = 20). D𝐸 = G(𝐿IJKLMJN∗ − 𝐿OPQRNS∗ )T + (𝑎IJKLMJN∗ − 𝑎OPQRNS∗ )T + (𝑏IJKLMJN∗ − 𝑏OPQRNS∗ )T (𝑬𝒒. 𝟑. 𝟑) 3.2.3.5. pH, titratable acidity, and total soluble solids Fruit pH, TA, and TSS was analyzed according to Yan et al. (2020) with slight modification. Ten berries from each replicate were used for the analyses. Berries were taken out from -80 °C freezer and kept at room temperature for 15 min, before being blended into puree by a magic bullet blender. Blueberry pH was determined by a pH meter (Corning pH/Ion analyzer 455, Corning Inc., NY, USA). Titratable acidity was measured by titration and expressed as citric acid equivalents (mg/g). Specifically, 1.5 g of puree was diluted 1:10 with deionized distilled water and titrated with 0.1 mol/L of NaOH (Fisher Scientific, Hampton, NH) until pH reached 28 8.2. Total soluble solids were measured by a digital refractometer (Reichert A2R200, Reichert GmbH, Seefeld, Germany) and expressed as °Brix. 3.2.4. Determination of antioxidant activity 3.2.4.1. Phenolic extraction Ten blueberries from each replicate were freeze-dried in separate petri-dishes using a freeze dryer (Labconco Corporation, Kansas City, MO, USA), and subsequently ground into fine powder using a coffee grinder. Phenolic compounds were extracted from freeze dried blueberries according to Pico et al. (2019). Briefly, 2 g of blueberry powder was mixed with 8mL of 80% methanol with 0.1% formic acid (v/v) in water and shaken for 15 min and centrifuged for 10 min at 3000 rpm and 4 °C. The pellet was re-extracted with 8 mL of 70% acetone with 0.1% formic acid (v/v) in water, shaking for another 15 min and centrifuging at the same conditions. Both supernatants were combined and the volume was adjusted to 20 ml with milli-Q water. The extracts were kept at freezing temperatures until antioxidant activity analysis were performed within the same day. 3.2.4.2. Free radical scavenging activity The antioxidant activity of the blueberry extracts, measured through the free radical scavenging activity, was analyzed by 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay, following Pico et al. (2019) with slight modification. 1.5 mg of DPPH were 29 dissolved in 50 mL of methanol (HPLC grade, ≥99.9%, Sigma-Aldrich, USA), from which 2 mL were placed in a spectrophotometric cuvette and measured absorbance at 517 nm (A0). Different aliquots of the phenolic extract (0, 2, 5, 10, 15, 25 µl) were added to 2mL of methanolic DPPH solution and the subsequent absorbance (A300) was measured at 517 nm for 300 seconds using an Ultrospec 3000 spectrophotometer (Pharmacia Biotech, USA). The percentage of inhibition was calculated according to the Equation 3.4. % Inhibition = _1 – aA300𝐴0 efx100 (𝐄𝐪. 𝟑. 𝟒) The IC50 value, which shows the amount of phenolic compound needed to inhibit 50% of DPPH free radicals, was calculated by interpolation from the semi-logarithmic curve analysis. 3.2.5. Statistical analyses One-way ANOVA was performed using SPSS v23.0 (IBM, New York, USA) to detect the significant effect (p < 0.05) of different PL doses on various blueberry quality traits according to Duncan’s Test. The data for each parameter was expressed as a mean of three biological replicates ± standard deviation (SD). 30 3.3. Results and discussion 3.3.1. Weight loss Weight loss is one of the most important factors affecting blueberry shelf-life, frequently used as a blueberry quality indicator. The PL treatments in this study effectively prevented weight loss during blueberry storage, compared to control treatment (Figure 3.2). Different doses of PL showed similar performance in preventing weight loss at week two, but a higher dose (i.e. 6 J cm-2 and 9 J cm-2) turned to be more efficient at week four and six. Nguyen et al. (2014) showed that UV-A, -B and -C at 0.6 J cm-2 reduced blueberry (cv. Duke) weight loss during 28-day storage at 0 °C. Respiration and transpiration lead to mass changes in fruits and vegetables when stored under the optimal conditions. The decreased fruit weight loss in the irradiation-treated samples could be related to the alteration of the cell integrity and pore sizes (Guimaraes et al., 2013). Our data showed that berries treated with PL doses of 6 J cm-2 and 9 J cm-2 had continuously lower weight loss than control during storage. This lower weight loss can be associated with higher penetration of higher doses of PL into the thick waxy cuticle which can lead to membrane permeability changes and less water loss. However, Cao et al. (2017) reported that blueberries treated with PL (6 J cm-2) showed increased weight loss during seven-day storage at 5 °C. There are some reports indicating that no significant effects of PL on weight loss in strawberries during eight-day storage at 6°C (Duarte-Molina et 31 al., 2016). Different results may be related to higher storage temperature, different RH%, or different types of cultivars or berries. Figure 3.2. Impact of pulsed light treatments on weight loss in blueberries (cv. Draper) during six-week storage at 0.5 °C and 90-95% RH 3.3.2. Rot incidence No rotted berries were observed in any treatments after two-week storage at 0.5 °C and 90-95% RH (Figure 3.3). None of the PL treatments in this study showed any effects on rot incidence during blueberry storage, in comparison with control treatment (Figure 3.3). Indeed, rotted berries were firstly observed in the PL treatment at 3 J cm-2 where the rot incidence was 5.67% at Week 4. Instead, control and other PL treatments didn’t show any rot symptoms until week 6. Berries treated with 9 J cm-2 of PL demonstrated the lowest value (9.88%) of rot incidence at week 6, however, this was not statistically significant. Cao et al. (2019) showed that PL treatment did not affect the fungal development on strawberries during four-week storage. The effectiveness of PL treatment is closely related to the type of microbe, inoculation site, and inoculum size (Huang and Chen, 2014). Bialka and Demiric (2007) reported that shadowing/shielding effect on the surface of raspberry and aaabababbcbbcb024681012142 4 6Weight Loss (%)Storage Time (Weeks)CNPL 3PL 6PL 9 32 strawberry could influence microbial reduction of PL treatment. PL treatment at 22.5 J cm-2 was shown to be more efficient in the reduction of Salmonella and E. coli in blueberries than in strawberries, due to their different topographical surface (Huang et al., 2017). Fig. 3.3. Impact of pulsed light treatments on rot incidence in blueberries (cv. Draper) during six-week storage at 0.5 °C and 90-95% RH 3.3.3. Firmness In all PL treatments, berry firmness tended to increase from week 0 to week 2 and then continuously decrease from week two and week six; whereas in control treatment, the firmness decreased from week zero to week six (Figure 3.4). Berries from any of the PL treatments were found to have lower firmness than control berries at week 0 (Figure 3.4). However, at week 2 and Week 4, berries from all PL treatments showed higher firmness than control berries, with the highest level found in PL dose at 9 J cm-2 at week 2 and 6 J cm-2 at Week 4 (Figure 3.4). After six-week 33 storage, berry firmness showed no difference among treatments (ranging from 478.2 to 495.3 g), except that a higher firmness was found in berries treated with PL at 6 J cm-2 (530.22 g). Cao et al. (2019) indicated that PL treatment in blueberries had no difference from the control in terms of fruit firmness. In addition, Rock et al. (2015) reported that PL treatment had no impact on the blueberry firmness one day after the treatment. Paniagua et al. (2014) reported that the dehydration due to low moisture loss conditions could lead to some microstructural changes in the outer cell layers of the fruit which are correlated to the firming of blueberries. Figure 3.4. Impact of pulsed light on firmness in blueberries (cv. Draper) during six-week storage at 0.5 °C and 90-95% RH 3.3.4. Color The color parameters of blueberries treated with different doses of PL are presented in Table 3.1. No differences were found in lightness (L*) and greenness (a*) in berries from all treatments during storage. This concurs with previous studies that suggested UV-C and PL treatments had no impact on the skin color of 34 strawberries during 28 days of the storage (Cao et al., 2019). However, blueberries treated with 9 J cm-2 of PL showed lower blueness (higher b* value) than any other treatments during storage, except for week 2 when 3 J cm-2 of PL treated blueberries showed the lowest blueness. This was in contrast to Rock et al. (2015) and Moreno et al. (2007) indicating that b* values in PL-treated or irradiated blueberries were higher compared to control. Pigment concentration could be changed by impact of irradiation on the cell structure which lead to change in b* value (Moreno et al., 2007). Moreover, Asen et al. (1972) demonstrated that the co-pigmentation of anthocyanins, which leads to the intense color variation in plant tissues can be affected by heating. In this study, it is likely that the higher dose of PL induced more heat on the samples and that dissociation of co-pigmentation of anthocyanins may have caused lower blueness in samples. Overall, the total color difference (ΔE) was calculated between each PL treatment and control treatment, which were less than 3 in all treatments during storage, signifying that the color difference after treatment were not high enough to be distinguished by the human eyes (Kurek et al., 2021). No differences were observed among PL treatments during storage, either. Table 3.1. Impact of pulsed light on blueberry (cv. Draper) color during six-week storage at 0.5 °C and 90-95% RH Color parameters Storage time (Weeks) Doses of PL 0 J cm-2 (control) 3 J cm-2 6 J cm-2 9 J cm-2 L* value 0 31.34±0.21 ABa 31.16±1.02 Aa 31.60±0.54 Aa 30.49±0.66 ABa 35 2 30.19±1.32 Ba 28.72±1.14 Aa 29.88±0.81 Ca 30.55±0.19 ABa 4 32.70±0.98 Aa 31.71±2.71 Aa 31.32±0.22 ABa 31.31±055 Aa 6 32.70±1.55 ABa 31.71±0.66 Aa 31.32±0.35 BCa 31.31±0.30 Ba b* value 0 -5.25±0.05 Aa -4.97±0.30 Aab -4.87±0.48 Aab -4.52±0.16 BCb 2 -5.41±0.32 Aa -4.67±0.40 Ab -4.80±0.32 Aab -4.83±0.20 Cab 4 -5.43±0.31 Aa -4.98±0.76 Aab -4.79±0.13 Aab -4.39±0.24 ABb 6 -5.43±0.58 Aa -5.24±0.41 Aa -4.90±0.21 Aa -4.12±0.16 Ab a* value 0 -0.27±0.08 Aa -0.21±0.02 Aa -0.21±0.02 Aa -0.20±0.06 BCa 2 -0.14±0.16 Aa -0.01±0.04 Aa -0.11±0.06 Aa -0.17±0.05 Ca 4 -0.18±0.11 Aa -0.26±0.38 Aa -0.19±0.03 Aa -0.18±0.06 ABa 6 -0.23±0.15 Aa -0.10±0.07 Aa -0.15±0.08 Aa -0.12±0.02 Aa DE value 0 - 0.88±0.58 Aa 0.69±0.31 Aa 1.17±0.75 Aa 2 - 2.25±1.13 Aa 1.39±0.13 Aa 1.32±0.80 Aa 4 - 1.81±0.64 Aa 1.53±1.10 Aa 1.75±0.53 Aa 6 - 1.63±1.69 Aa 1.30±0.53 Aa 1.91±1.21 Aa Different lowercase letters indicate significant difference (p < 0.05) among treatments and different uppercase letters indicate significant difference (p < 0.05) during storage according to a Duncan’s Test. Data are expressed as the mean value of three replicates ± standard deviation (SD, n = 3). 3.3.5. pH, titratable acidity, and total soluble solids The impact of PL treatments on the levels of TSS, pH, and TA during blueberry storage are demonstrated in Table 3.2. The level of total soluble solids increased during the six-week storage of blueberries from all treatments. Total soluble solids were at a similar level among all treatments at week 0 and week 2. Berries treated with 9 J cm-2 of PL obtained a higher TSS level at Week 4 than that treated with 6 J 36 cm-2 of PL, other than that, there is no difference found at this stage. Similarly, berries treated with 6 J cm-2 of PL had the lowest TSS at week 6, whereas control berries showed the highest TSS at this stage. However, TSS increased significantly (p< 0.05) at week 6 in control samples with value of 15.8° compared to PL treated berries with range from 14.48° to 15.03°. Moreover, no significant changes were observed in TSS of 3 and 6 J cm-2 of PL treated samples until Week 4. Weight loss during the storage can lead to increase the concentration of TSS (Giuggioli et al., 2013). In addition, previous research showed that TSS decreased in irradiated blueberries during the storage time (Moreno et al., 2007), which can be related to lower weight loss in PL treated samples. As Table 3.2 shows, no significant difference (p≥ 0.05) in pH was observed in all PL treated samples and also in all controlled samples from week 0 to week 6. However, control samples with pH value of 3.94 showed significantly higher pH than the PL treated samples, ranging from 3.78 to 3.84 after 48 days. Lower pH in PL treated samples than control can also be attributed to senescence delay due to pulsed UV treatment which can help control microbial growth resulting in prolonging the shelf-life of the berries. Titratable acidity level decreased in berries from all treatments during storage. PL treated samples showed no significant differences (p ≥ 0.05) by Week 4. Nevertheless, at the end of the storage (week 6), control and PL dose of 3 J cm-2 37 treatment showed lower acidity (3.67and 3.72 respectively) than PL doses of 6 J cm-2 and 9 J cm-2 treatments (4.11 and 4.15 respectively). This agrees with Nguyen et al. (2014) in which higher acidity was observed in UV light-treated samples than those untreated ones. The degradation of organic acids (e.g. citric, malic, quinic and chlorogenic acids) during storage has been reported to cause a decrease in TA at the end of the storage period. It also can be seen the berry fruits showed tolerance to lower PL dose (3 J cm-2) possibly because of their thick waxy cuticles. Table 3.2. Impact of pulsed light on blueberry (cv. Draper) total soluble solid (TSS), pH, and titratable acidity (TA) during six-week storage at 0.5 °C and 90-95% RH Fruit quality parameters Storage time (Weeks) Doses of PL 0 J cm-2 (control) 3 J cm-2 6 J cm-2 9 J cm-2 TSS (◦Brix) 0 13.76±0.29 Ca 14.17±0.15 Ba 14.08±0.35 Ba 13.98±0.02 Ca 2 14.35±0.35 Ba 14.16±0.17 Ba 14.02±0.02 Ba 14.36±0.16 Ba 4 14.33±0.33 Bab 14.53±0.31 Bab 14.08±0.07 Bb 14.62±0.08ABa 6 15.80±0.00 Aa 15.03±0.25 Ab 14.48±0.16 Ac 14.92±0.29 Ab pH 0 3.75±0.08 Aa 3.75±0.07 Aa 3.63±0.03 Aa 3.54±0.07 Aa 2 3.78±0.04 Aa 3.76±0.10 Aa 3.80±0.14 Aa 3.80±0.01 Aa 4 3.81±0.04 Ab 3.65±0.02 Ac 3.91±0.03 Aa 3.79±0.01 Ab 6 3.94±0.03 Aa 3.84±0.01 Ab 3.78±0.01 Ab 3.81±0.04 Ab TA (mg/mL) 0 4.63±0.25 Aa 4.48±0.08 Aa 4.57±0.10 Aa 4.77±0.10 Aa 2 4.22±0.09 Bb 4.46±0.10 Aa 4.41±0.13 Aab 4.59±0.10 Aa 4 4.05± 0.21 Ba 4.07±0.13 Ba 4.08±0.05 Ba 4.11±0.11 Ca 6 3.67±0.08 Cb 3.72±0.10 Bb 4.11±0.09 Ba 4.15±0.09 Ba 38 Different lowercase letters indicate significant difference (p < 0.05) among treatments and different uppercase letters indicate significant difference (p < 0.05) during storage according to a Duncan’s Test. Data are expressed as the mean value of three replicates ± standard deviation (SD, n = 3). 3.3.6. DPPH free radical scavenging activity The IC50 value increased during the six-week storage in all treatments, indicating a decrease in the antioxidant activity. The IC50 value in all PL treated berries were significantly higher than control berries (0.54 mg/mL) at harvest, and higher doses of PL (6 J cm-2 and 9 J cm-2) further increased the value compared to a lower dose (3 J cm-2) (Figure 3.4). Therefore, control berries showed the highest antioxidant activity at harvest. Generally, the antioxidant activity was consistently higher in control berries compared to PL treated berries during the six-week storage in this study. In contrast, Nguyen et al. (2014) indicated that UV-B and UV-C treatments increased the antioxidant activity in highbush blueberries (cv. Duke) during 28-day storage, in comparison with the untreated samples. Previous research reported enhanced flavonoid level and antioxidant capacity in blueberries after being exposed to UV-C. This was possibly due to the induced stress through UV-C radiation, which might have triggered the defense mechanism of blueberries. Lower dose of UV-C illumination (0.43–2.15 kJ m -2) have been demonstrated to increase the total phenols and anthocyanins in blueberries, while a higher dose showed the reverse effect (Wang et al. 2017). Similarly, Perkins-Veazie et al. (2008) reported that higher doses of UV-C treatment tended to induce injury in strawberries. Moreover, Oms-Oliu et 39 al. (2010) showed that PL treatments decreased or increased the antioxidant activity in mushrooms, which could be associated with doses of the PL that can affect the key enzymes involved in the stress responses of the plant, which may in turn lead to degradation of phenolics and polymerization of the quinones. Figure 3.4. Impact of pulsed light on antioxidant activity in blueberries (cv. Draper) during six-week storage at 0.5 °C and 90-95% RH 3.4. Conclusion Different pulsed light treatments were applied to highbush blueberries (cv. Draper) at harvest and were stored at 0.5 °C and 90-95% RH for six weeks. Blueberry quality traits, including color, firmness, weight loss, and rot incidence, TSS, pH, TA, and antioxidant capacity were assessed after treatment and biweekly during storage. Generally, higher doses of PL (i.e. 6 J cm-2, and 9 J cm-2) performed well in maintaining the basic fruit quality traits (e.g., weight loss, rot incidence, firmness, and skin color) compared to control, while a lower dose (i.e. 3 J cm-2) was less effective. Blueberry flavor changed during postharvest storage, with the TSS level increased and the TA level decreased in all treatments. Control berries obtained 40 the highest TSS level and the lowest TA level after the six-week storage. The antioxidant was observed to increase in all treatments during storage; control berries showed the highest antioxidant activity at the end of storage, and a higher dose of PL (6 J cm-2 and 9 J cm-2) tended to decrease the antioxidant activity compared to a lower dose (3 J cm-2). Therefore, a higher dose (6 J cm-2) of pulsed light treatment performs well in the preservation basic fruit quality traits and extension of shelf-life in blueberries. This study found that PL treatments showed a positive influence on most general quality of blueberries and could prolong their shelf-life to six weeks, which has implications for the industry. 41 Chapter 4: Investigating the quality and shelf-life of PL treated blueberries under CAS 4.1. Introduction Controlled atmosphere storage (CAS) is one of the most effective technologies in perishable fruit and vegetables at the post-harvest storage to improve their quality and shelf-life. Controlled atmosphere storage involves reduced concentration of oxygen (O2) and increased concentration of carbon dioxide (CO2) which needs to be continuously monitored. Temperature and the respiratory gases are two most main factors affecting the respiration rate (Liu et al., 2019). The low respiration rate could lead to slow down the senescence process in fruits. Therefore, CAS combined with proper refrigeration can extend post-storage life of fresh fruits and vegetables (Wills et al., 2007). The shelf-life of the blueberries stored at near 0ºC depends on cultivar, stage of ripeness, method of harvest, and storage conditions changes between 14 and 20 days (Matiacevich et al., 2013). Controlled atmosphere storage (CAS) is used commercially for exporting fresh blueberries to improve the berry shelf-life. A high CO2 concentration can eliminate the decay growth in the blueberries (Retamales and Hancock, 2018). The recommended CAS for the blueberries is 8% to 15% of CO2 and 1% O2 concentration to prevent fermentation damage. In addition, some research shows that O2 concentrations between 1% and 10% can help prevent further decay (Paniagua et al., 2014). 42 Pulsed light (PL) technology is an innovative non-thermal food processing technology which has shown a great potential to inactivate microbial spoilage caused by fungi, bacteria, and yeasts of the food product such as strawberries, spinach, bell peppers, raspberries and blueberries (Bialka & Demirci, 2008, Huang et al. 2017, Wiktor et al., 2019). PL applies a short duration of high-intensity of white lights (wavelength range of 200–1100 nm) to inactive microorganism. The ultra-violet (UV) region of the spectrum is attributed to microbial destruction in food products. Significant reduction in microbial growth which leads to reduce risk of foodborne pathogens on public health, shelf-life extension, low impact on the environment with high adjustability are the major advantages of PL (Oms-Oliu et al., 2010; Bhavya & Umesh Hebbar, 2017). In this study, we combined the innovative post-harvest strategies, PL and CAS, to minimize the processing limits to improve the quality and extend the shelf-life of highbush blueberries grown in BC. With the growing demand for non-thermal processing, this information provides a better understanding of the impact of combination of PL and CAS technologies on prolonging the shelf-life storage of blueberries which has been little focus while a number of studies indicate safety and efficacy of PL technology on microbial load reduction in fruit and vegetables. Studies in this vein can potentially enhance our understanding of the ways in which 43 quality and safety of fruit can be better maintained, which has important industrial implications. 4.2. Materials and methods 4.2.1. Blueberry Samples The highbush blueberries (Draper cultivars) for this research were provided in mid-August by the British Columbia Blueberry Council (Abbotsford, BC, Canada) and were hand-harvested from a local farm in Columbia Valley, Abbotsford. The samples were promptly transferred to the Food, Nutrition and Health laboratory at the University of British Columbia, where they were immediately stored at 4 °C for one hour. Twenty intact samples with no sign of visible defects, and with uniform color and size were selected per 4.4 oz (130.12 ml) clamshell. As Figure 4.1 shows each sample treated with three different PL doses (3 J cm-2, 6 J cm-2, 9 J cm-2) and was separately placed in four different control atmosphere chambers (8 kPa CO2 + 1.5 kPa O2; 8 kPa CO2 + 10 kPa O2; 15 kPa CO2 + 1.5 kPa O2; 15 kPa CO2 + 10 kPa O2), and air (0.5 kPa CO2 + 20.7 kPa O2) with no PL treatment as a control. The blueberries were analyzed at weeks 0, 2, 4 and 6. 44 Figure 4.1. Pulsed light processing of blueberries (cv. Draper) maintained in controlled atmosphere storages 45 4.2.2. Controlled Atmosphere Storage and Pulsed Light Treatments In the first stage, a complete block factorial design was used to optimize the concentration of Oxygen (O2) and Carbon dioxide (CO2) of the controlled atmosphere for the draper cultivars. Four clear desiccator cabinets (Cleatech LLC, Orange, CA, USA) with the dimensions of 10"W x 14"D x 10"H including gas in-ports and hygrometers to monitor temperature and RH were used to store berry clamshells. They were placed at recommended refrigerator condition at 0.5°C with 95% RH for 6 weeks (Perkins-Veazie, 2016). To create four different controlled atmosphere storages, four certified standard gas cylinder tanks (Praxair Canada Inc., Vancouver, BC, Canada) composed of O2, CO2, and nitrogen to balance the gas blends were used. Gas concentrations in the desiccator cabinets were checked every morning by using a O2/CO2 gas analyser (Mocon Checkpoint 3, Meyer Service & Supply Ltd, Ontario, Canada) and each cabinet was re-charged upon the gas reduction. Regarding the PL treatments, they were carried out by the PL equipment explained in Chapter 3, with the same doses (3 Jcm-2, 6 Jcm-2, and 9 Jcm-2) and distance from PL lamp (5cm). The PL treated and untreated samples were maintained in the refrigerator (Hoshizaki, B & G Refrigeration, FL, USA) at 0.5°C with RH of 90%-95% and under four CAS conditions and regular atmosphere storage (air, Control) until week 46 6. The quality parameters (i.e. color, firmness, rot incidence, and weight loss) of the fresh berries were analyzed after harvest and bi-weekly for 6 weeks. For analyzing physicochemical traits (pH, titratable acidity, and total soluble solids), and antioxidant activity of the samples, they were taken out from the refrigerator at the same stage and stored at -80°C until further analyses. 4.2.3. Methods The berry qualities (i.e. colour, firmness, weight loss, rot incidence), antioxidant activity, and Physicochemical attributes (pH, titratable acidity, total soluble solid) were assessed at weeks 0, 2, 4, and 6 for all treated and controlled samples with the same methodologies explained in Chapter 3. 4.2.4. Design of Experiment Table 4.1 displays the design of the experiments composed of 80 trials. A response surface methodology with full factorial design was utilized to analyze the impact of pulsed light with three different doses (3, 6, 9 J cm-2) and four CAS with two levels of O2 (1.5 kPa and 10 kPa) and CO2 (8 kPa and 15 kPa) on the weight loss (%), firmness(g), total soluble solid (TSS, ◦Brix), titratable acidity (TA, %), and 1,1-diphenyl-2-picryl hydrazyl (DPPH) free radical scavenging activity (IC50, mg/mL) during six weeks of storage. Three replicates were used for all analyses. The experimental design and analysis of variance (ANOVA) were conducted using 47 Design-Expert Software Version 13 (Minneapolis, USA). The optimal conditions were obtained by Design-Expert Software. For the optimization process of the conditions, some response variable (weight loss, rot incidence, TSS, TA) were either minimized or maximized based on desirability function during the storage time. Table 4.1. Values of weight loss, firmness, DPPH free radical scavenging activity (IC50), total soluble solids (TSS), and titratable acidity (TA) of blueberries (cv. Draper) affected by pulsed light, storage time, O2 and CO2 concentrations at 0.5 °C and 90-95% RH Run A: Pulsed Light (J cm-2) B: Time of Storage (Weeks) C: Oxygen (kPa) D: Carbon dioxide (kPa) Rot Incidence (%) Weight Loss (%) Firmness (g) IC50 (mg/mL) TSS (◦Brix) TA (%) 1 0 0 21 0.5 - - 728.67±0.14 0.54±0.02 13.76±0.29 4.63±0.25 2 3 0 21 0.5 - - 634.10±0.91 0.61±0.04 14.17±0.15 4.48±0.08 3 6 0 21 0.5 - - 653.73±46.6 0.68±0.03 14.08±0.35 4.57±0.10 4 9 0 21 0.5 - - 676.10±29.29 0.68±0.01 13.98±0.02 4.77±0.11 5 0 0 1.5 8 - - 729.85±15.97 0.56±0.02 13.74±0.29 4.46±0.31 6 3 0 1.5 8 - - 710.52±51.92 0.57±0.03 14.50±0.07 4.5±0.03 7 6 0 1.5 8 - - 698.42±19.08 0.68±0.09 14.20±0.47 4.08±0.22 8 9 0 1.5 8 - - 665.16±11.85 0.60±0.02 14.30±0.19 4.13±0.15 9 0 0 10 8 - - 729.30±24.21 0.55±0.02 14.18±0.46 4.87±0.24 10 3 0 10 8 - - 738.65±40.38 0.58±0.73 13.93±0.23 4.33±0.13 11 6 0 10 8 - - 724.79±19.62 0.68±0.01 13.87±0.53 4.56±0.24 12 9 0 10 8 - - 759.82±56.06 0.67±0.03 14.23±0.42 4.12±0.13 13 0 0 1.5 15 - - 769.13±5.61 0.54±0.02 14.22±0.24 4.72±0.06 14 3 0 1.5 15 - - 780.14±39.94 0.56±0.03 14.57±0.49 4.61±0.34 15 6 0 1.5 15 - - 710.21±42.73 0.66±0.03 14.80±0.67 4.6±0.24 16 9 0 1.5 15 - - 726.57±31.51 0.65±0.03 14.67±0.24 4.8±0.22 17 0 0 10 15 - - 728.94±18.13 0.58±0.01 14.39±0.46 4.38±0.01 18 3 0 10 15 - - 780.84±38.77 0.67±0.04 14.53±0.38 4.65±0.04 19 6 0 10 15 - - 752.35±16.02 0.68±0.04 14.13±0.43 4.65±0.04 20 9 0 10 15 - - 777.06±52.68 0.70±0.03 14.52±0.02 4.60±0.12 21 0 2 21 0.5 0 5.40±0.12 717.17±11.87 0.54±0.02 14.35±0.35 4.22±0.09 22 3 2 21 0.5 0 4.44±0.22 751.07±17.27 0.68±0.01 14.16±0.17 4.46±0.14 48 23 6 2 21 0.5 0 3.89±0.50 768.14±16.01 0.67±0.02 14.02±0.02 4.41±0.13 24 9 2 21 0.5 0 3.97±0.36 804.54±11.78 0.68±0.02 14.36±0.16 4.59±0.12 25 0 2 1.5 8 0 1.43±0.26 795.10±63.38 0.60±0.04 13.29±0.06 4.32±0.23 26 3 2 1.5 8 0 0.77±0.30 781.15±26.85 0.60±0.06 14.06±0.51 4.22±0.28 27 6 2 1.5 8 0 1.59±0.37 789.54±27.74 0.61±0.02 14.02±0.28 4.03±0.23 28 9 2 1.5 8 0 1.29±0.25 736.48±22.87 0.61±0.07 14.19±0.46 3.81±0.04 29 0 2 10 8 0 0.81±0.23 829.75±63.25 0.58±0.04 13.80±0.14 4.47±0.23 30 3 2 10 8 0 0.83±0.04 845.77±3.52 0.62±0.01 13.60±0.32 4.35±0.14 31 6 2 10 8 0 0.64±0.39 831.94±45.44 0.69±0.03 13.67±0.23 4.45±0.02 32 9 2 10 8 0 0.68±0.29 832.94±51.64 0.66±0.03 14.12±0.33 4.51±0.04 33 0 2 1.5 15 0 1.09±0.64 780.44±51.77 0.58±0.06 14.24±0.19 4.26±0.36 34 3 2 1.5 15 0 0.59±0.22 733.56±17.88 0.66±0.08 14.31±0.24 4.62±0.12 35 6 2 1.5 15 0 0.66±0.28 737.91±18.32 0.70±0.01 14.13±0.46 4.28±0.01 36 9 2 1.5 15 0 0.74±0.31 784.72±10.28 0.61±0.02 14.18±0.39 4.4±0.35 37 0 2 10 15 0 2.81±0.65 829.50±60.19 0.57±0.06 14.26±0.53 4.48±0.3 38 3 2 10 15 0 2.13±0.62 868.27±6.12 0.61±0.02 14.07±0.34 4.39±0.22 39 6 2 10 15 0 1.32±0.25 764.97±45.63 0.70±0.09 14.09±0.51 4.46±0.42 40 9 2 10 15 0 1.20±0.45 783.66±12.85 0.67±0.01 14.43±0.12 4.41±0.22 41 0 4 21 0.5 0 9.80±0.34 556.88±0.65 0.63±0.02 14.33±0.33 4.05±0.21 42 3 4 21 0.5 5.67±5.41 9.02±0.75 677.84±15.75 0.75±0.02 14.53±0.31 4.07±0.17 43 6 4 21 0.5 0 7.89±0.87 711.77±0.85 0.77±0.02 14.08±0.07 4.08±0.05 44 9 4 21 0.5 0 6.80±0.77 684.98±0.70 0.76±0.01 14.62±0.08 4.11±0.11 45 0 4 1.5 8 2.43±2.22 2.32±0.32 680.38±43.43 0.71±0.04 13.87±0.03 3.98±0.25 46 3 4 1.5 8 5.53±4.92 1.74±0.06 766.14±59.06 0.80±0.02 13.89±0.48 4.16±0.15 47 6 4 1.5 8 13.78±4.34 2.66±0.53 713.37±36.89 0.80±0.01 14.09±0.48 3.87±0.08 48 9 4 1.5 8 3.47±3.02 1.93±0.63 713.17±13.06 0.70±0.06 14.18±0.42 4.00±0.26 49 0 4 10 8 0 2.70±0.45 787.95±38.65 0.70±0.06 14.57±0.89 3.88±0.10 50 3 4 10 8 0 1.37±0.07 703.54±15.16 0.71±0.02 13.70±0.09 4.15±0.13 51 6 4 10 8 0 1.66±0.47 703.52±40.92 0.72±0.00 14.2±0.66 3.84±0.46 52 9 4 10 8 0 1.74±0.30 790.05±11.04 0.73±0.05 14.05±0.35 4.05±0.37 53 0 4 1.5 15 0 1.60±0.71 681.58±11.26 0.66±0.06 13.33±0.43 4.46±0.28 54 3 4 1.5 15 0 1.09±0.33 663.44±9.82 0.67±0.03 13.68±0.26 4.40±0.12 55 6 4 1.5 15 0 1.23±0.48 659.06±31.89 0.73±0.03 13.87±0.14 4.27±0.30 56 9 4 1.5 15 0 1.33±0.53 658.57±16.78 0.75±0.05 13.92±0.40 4.47±0.02 57 0 4 10 15 0 4.97±0.56 728.12±47.93 0.70±0.03 13.67±0.23 4.15±0.17 49 58 3 4 10 15 1.91±1.76 4.58±0.29 771.48±18.08 0.67±0.05 14.5±0.15 4.04±0.28 59 6 4 10 15 0 2.81±0.25 714.64±24.68 0.76±0.05 14.42±0.12 4.00±0.15 60 9 4 10 15 0 2.37±0.76 738.82±36.23 0.75±0.05 13.52±0.07 4.32±0.12 61 0 6 21 0.5 17.91±4.9 13.01±0.89 495.27±1.47 0.72±0.01 15.8±0.04 3.67±0.08 62 3 6 21 0.5 13.65±3.24 12.86±0.78 478.18±27.15 0.83±0.02 15.03±0.25 3.72±0.10 63 6 6 21 0.5 18.25±6.64 10.94±0.43 530.22±14.12 0.84±0.01 14.48±0.16 4.11±0.09 64 9 6 21 0.5 9.89±5.99 10.58±0.49 486.87±15.16 0.89±0.01 14.92±0.29 4.15±0.09 65 0 6 1.5 8 25.63±1.43 3.60±0.50 502.26±57.71 0.89±0.03 13.57±0.12 3.81±0.15 66 3 6 1.5 8 15.26±1.82 2.91±0.28 491.23±48.57 0.90±0.07 14.24±0.02 4.23±0.13 67 6 6 1.5 8 15.93±4.17 3.05±0.59 517.99±18.90 0.85±0.08 13.83±0.06 4.04±0.01 68 9 6 1.5 8 19.57±2.85 1.63±0.50 512.47±35.82 0.87±0.04 14.08±0.08 3.62±0.42 69 0 6 10 8 2.63±0.90 4.06±0.67 535.76±61.11 0.82±0.06 13.77±0.03 4.05±0.31 70 3 6 10 8 6.80±0.42 3.84±0.36 551.30±38.04 0.82±0.06 13.67±0.47 4.01±0.39 71 6 6 10 8 6.73±0.71 3.01±0.43 559.87±32.42 0.82±0.05 14.12±0.13 3.85±0.55 72 9 6 10 8 4.96±0.41 2.71±0.57 574.25±15.01 0.82±0.04 13.88±0.32 4.02±0.21 73 0 6 1.5 15 4.27±1.49 2.10±0.71 438.98±10.90 0.75±0.05 13.43±0.27 4.12±0.55 74 3 6 1.5 15 0 1.66±0.22 435.71±18.70 0.82±0.07 13.52±0.02 4.34±0.29 75 6 6 1.5 15 2.70±0.10 1.67±0.63 435.31±12.62 0.79±0.03 13.34±0.23 4.10±0.18 76 9 6 1.5 15 3.14±2.73 1.42±0.53 470.79±16.38 0.80±0.06 13.75±0.15 4.17±0.10 77 0 6 10 15 4.79±4.79 6.75±0.71 595.30±41.57 0.81±0.07 14.36±0.20 4.04±0.01 78 3 6 10 15 3.68±1.04 6.32±0.42 529.21±58.34 0.76±0.06 14.27±0.39 3.82±0.05 79 6 6 10 15 2.80±1.84 4.26±0.63 529.97±35.12 0.81±0.06 13.67±0.39 3.81±0.02 80 9 6 10 15 0 3.43±0.45 463.46±28.46 0.82±0.03 13.80±0.07 3.87±0.06 Data are expressed as the mean value of three replicates ± standard deviation (SD, n = 3). 4.3. Results and Discussion: 4.3.1. Color The color of the blueberries is a very important factor that impacts the consumer acceptance in the fresh market. The surface color L*, a*, and b* define lightness, red/green and yellow/blue value respectively. Figure 4.2 (b,c) illustrates storage time 50 (B) and O2 concentration (C) had no significant effect (p≥ 0.05) on the L* value; however Figure 4.2 (a,d) demonstrates that PL (A) and CO2 concentration (D) showed a significant effect (p < 0.05). It displays that a rise in PL doses resulted in lower lightness in the blueberry while an increased in CO2 concentration led to an increase in the lightness of blueberries. Nonetheless no significant effect (p≥ 0.05) of the interaction between variables was observed in terms of lightness of the blueberries. In contrast, the previous finding of Cao et al. (2019) showed that UV-C which is an important part of pulsed light and PL treatments had no significant effect on L* value of strawberries during 28 days of the storage. Furthermore, Schotsmans et al. (2006) found that L* value of two blueberry cultivars were similar at regular atmosphere storage and CAS (2.5 kPa O2 + 15 kPa CO2) during 28 days of storage. 51 Actual Factors: A=4.5, B=6, C=11, D=8 Figure 4.2. Effect of pulsed light (A), time of storage (B), O2 concentration (C), and CO2 concentration (D) on lightness (L*) of highbush blueberries (cv. Draper), where A, C, D are at the center point of the design and B is at week 6. A: Pulsed Light (J/cm2)0 1 2 3 4 5 6 7 8 9L*28.0029.0030.0031.0032.0033.0034.00Factor Coding: ActualActual FactorsA = 4.5B = 6C = 11D = 8B: Time of storage (Weeks)0 1 2 3 4 5 6L*28.0029.0030.0031.0032.0033.0034.00C: Oxygen (kPa)2 6 11 16 21L*28.0029.0030.0031.0032.0033.0034.00D: Carbon dioxide (kPa)1 4 8 11 15L*28.0029.0030.0031.0032.0033.0034.00a d c b 52 In the case of b* color, PL, O2 and CO2 concentrations, and the mutual interaction of PL and CO2 concentration indicated significant effect (p < 0.05) on the berry samples (Figure 4.3 and 4.4 [a]). In terms of interaction effects, with increasing PL doses and CO2 concentration, the blueness of samples increased; however, with applying higher doses of PL the blueness of samples was reduced. The a* value depended significantly (p < 0.05) on storage time (which enhanced the redness of samples until week 6), and the interaction between PL and storage time, CO2 concentration and storage time, and CO2 concentration and O2 concentration (4.4 [b]). In line with our results, some previous studies denoted that blueberries treated by PL or UV irradiation showed lower blueness than the control (Rock et al., 2015). The irradiation effect on the cell structure can change the pigment concentration which results in b* value changes (Moreno et al., 2007). Moreover, previous studies found that strawberries in 5 kPa O2+15 kPa CO2, or 10 % O2+20 % CO2 had higher L* and a* than regular atmosphere (Holcroft et al., 1999). 53 Actual Factors: A=4.5, B=6, C=11, D=8 Figure 4.3. Effect of pulsed light (A), time of storage (B), O2 concentration (C), and CO2 concentration (D) on blueness (b*) of highbush blueberries (cv. Draper), where A, C, D are at the center point of the design and B is at week 6. A: Pulsed Light (J/cm2)0 1 2 3 4 5 6 7 8 9b*-6.5-6-5.5-5-4.5-4-3.5Factor Coding: Actualb*Actual FactorsA = 4.5B = 6C = 11D = 8B: Time of storage (Weeks)0 1 2 3 4 5 6b*-6.5-6-5.5-5-4.5-4-3.5C: Oxygen (kPa)2 6 11 16 21b*-6.5-6-5.5-5-4.5-4-3.5D: Carbon dioxide (kPa)1 4 8 11 15b*-6.5-6-5.5-5-4.5-4-3.5a b d c b 54 Figure 4.4. (a) Response surface of the blueness of highbush blueberries (cv. Draper) affected by CO2 concentration and pulsed light, (b) Response surface of the redness (a*) of highbush blueberries (cv. Draper) affected by CO2 concentration and O2 concentration 4.3.2. Rot incidence As seen in Table 4.2, rot incidence was significantly influenced (p < 0.05) by PL, storage period of six weeks, CO2 concentration, and the mutual interaction between storage time and PL (AB – Figure 4-6), storage time and O2 concentration (BC), storage time and CO2 concentration (BD), O2 and CO2 concentration (CD – Figure 4-6). Furthermore, the quadratic interaction of PL, storage time, and O2 concentration showed significant effects (p < 0.05) on the decay of the berry samples. The quadratic equation has been provided in Equation 4.1 with a coefficient of regression (R2) of 0.7805. 𝑅𝑜𝑡 𝐼𝑛𝑐𝑖𝑑𝑒𝑛𝑐𝑒 (%) = 0.514024 + 0.215099 𝐴 + 1.34187 𝐵 − 0.71123 𝐶 − 0.04241 𝐷 − 0.04126 𝐴𝐵 − 0.0916 𝐵𝐶 − 0.1528 𝐵𝐷+ 0.034485 𝐶𝐷 − 0.01768 𝐴T + 0.375988 𝐵T + 0.030881 𝐶T (𝑬𝒒. 𝟒. 𝟏) 1 4 8 11 15 0 1 2 3 4 5 6 7 8 9-6.5 -6 -5.5 -5 -4.5 -4 -3.5 b*A: Pulsed Light (J/cm2)D: Carbon dioxide (kPa)Factor Coding: Actualb*-6.096 -3.9348X1 = AX2 = DActual FactorsB = 6C = 111 4 8 11 15 2 6 11 16 21-0.60 -0.40 -0.20 0.00 0.20 0.40 a*C: Oxygen (kPa)D: Carbon dioxide (kPa)Factor Coding: Actuala*-0.47 0.30X1 = CX2 = DActual FactorsA = 4.5B = 6b a X1= A X2= D Actual Factors B= 6 C= 11 X1= C X2= D Actual Factors A= 4.5 B= 6 55 Table 4.2. Analysis of Variance (ANOVA) for the impact of pulsed light, storage time, O2 and CO2 concentrations on rot incidence of blueberries (cv. Draper) at 0.5 °C and 90-95% RH Parameter IC50 (mg/mL) Type III SS F Value Pr > F Model 1375.79 59.8 < 0.0001*** A-Pulsed Light 9.52 4.55 0.0342* B-Time of storage 964.97 461.39 < 0.0001*** C-Oxygen concentration 0.651 0.3113 0.5776 D-Carbon dioxide concentration 10.07 4.81 0.0295* AB 15.65 7.48 0.0068* BC 162.3 77.6 < 0.0001*** BD 292.09 139.66 < 0.0001*** CD 39.32 18.8 < 0.0001*** A2 4.95 2.37 0.1255 B2 404.49 193.4 < 0.0001*** C2 44 21.04 < 0.0001*** *p < 0.05; ** p < 0.005; *** p < 0.0005. The study showed that there were no rotten berries in any treatments until week 4 of the storage at 0.5 °C and 90-95% RH. In addition, increased CO2 level (15 KPa) showed less rotten berries at week 4 and 6 in all treatments. It has been found that an increase in PL doses and CO2 concentration could cause a lower incidence of rotten berries during six weeks of storage (Figure 4.5). The finding from Cao et al. (2019) demonstrated that PL treatment had no effect on fungal growth of the strawberry samples during four weeks of storage. Huang et al. (2017) showed that 56 the effect of microbial reduction of PL treatment could be affected by shadowing effect on strawberry surfaces. In case of CAS, similar to our study, numerous researches reported that high CO2 level from 10–24% could reduce decay in blueberries (Harb and Streif, 2004; Paniagua et. al., 2014). Moreover, it has been found that high CO2 concentration (15 kPa) could reduce Botrytis rots of strawberries during 14 days of storage (Alamar et al., 2017). High CO2 concentration can suppress the enzyme activity which associated with the respiration of microorganisms resulting in reducing pathogen metabolism (Paniagua, 2012). 57 Actual Factors: A=4.5, B=6, C=11, D=8 Figure 4.5. Effect of pulsed light (A), time of storage (B), O2 concentration (C), and CO2 concentration (D) on rot incidence of highbush blueberries (cv. Draper), where A, C, D are at the center point of the design and B is at week6. A: Pulsed Light (J/cm2)0 1 2 3 4 5 6 7 8 9Rot Incidence (%)-505101520Factor Coding: ActualRot Incidence (%)Actual FactorsA = 4.5B = 6C = 11.25D = 7.75B: Time of storage (Weeks)0 1 2 3 4 5 6Rot Incidence (%)-505101520C: Oxygen (kPa)1.5 5.4 9.3 13.2 17.1 21Rot Incidence (%)-505101520D: Carbon dioxide (kPa)0.5 3.4 6.3 9.2 12.1 15Rot Incidence (%)-505101520a d c b 58 Figure 4.6. Response surface of weight loss of highbush blueberries (cv. Draper) affected by (a) time of storage and pulsed light, (b) O2 concentration and time of storage, (c) CO2 concentration and time of storage, (d) CO2 concentration and O2 concentration. 4.3.3. Weight loss and firmness Table 4.3 shows the analysis of variance of data in weight loss and firmness of blueberry samples treated by PL and different concentrations of O2 and CO2 during 6 weeks of the storage. For analysis of data, a quadratic model was used for all of the variances. The data in table 4.3 indicates that time of storage (B), O2 0 1 2 3 4 5 6 0 1 2 3 4 5 6 7 8 9-5 0 5 10 15 20 Rot Incidence (%)A: Pulsed Light (J/cm2)B: Time of storage (Weeks)Factor Coding: ActualRot Incidence (%)0 16.5417X1 = AX2 = BActual FactorsC = 11.055D = 8.041.5 5.4 9.3 13.2 17.1 21 0 1 2 3 4 5 6-5 0 5 10 15 20 Rot Incidence (%)B: Time of storage (Weeks)C: Oxygen (kPa)Factor Coding: ActualRot Incidence (%)0 16.5417X1 = BX2 = CActual FactorsA = 4.5D = 8.040.5 3.4 6.3 9.2 12.1 15 0 1 2 3 4 5 6-5 0 5 10 15 20 Rot Incidence (%)B: Time of storage (Weeks)D: Carbon dioxide (kPa)Factor Coding: ActualRot Incidence (%)0 16.5417X1 = BX2 = DActual FactorsA = 4.5C = 11.0550.5 3.4 6.3 9.2 12.1 15 1.5 5.4 9.3 13.2 17.1 21-5 0 5 10 15 20 Rot Incidence (%)C: Oxygen (kPa)D: Carbon dioxide (kPa)Factor Coding: ActualRot Incidence (%)0 16.5417X1 = CX2 = DActual FactorsA = 4.5B = 6b a d c X1= A X2= B Actual Factors C= 11 D= 8 X1= B X2= C Actual Factors A= 4.5 D= 8 X1= B X2= D Actual Factors A=4.5 C=11 X1= C X2= D Actual Factors A= 4.5 B= 6 59 concentration (C) and CO2 concentration (D) have significant effect (p < 0.05) on the weight loss and firmness; nevertheless, the PL doses showed that they could only have significant influence (p < 0.05) on weight loss. The mutual interaction between all variables (AB, AC, AD, BC, BD, CD) was significant (p < 0.05) for the weight loss (Figure 4.7). However, only in the case of firmness, the effect of mutual interaction of the storage time and CO2 concentration (BD) was significant (p < 0.05). The effect of quadratic interaction of O2 concentration (C2) was significant for both firmness and weight loss, while the quadratic interaction of the storage time (B2) was only significant for the firmness. The quadratic interaction of PL only significantly affected the weight loss. Equations 4.2 and 4.3 indicated the developed models with a high coefficient of regression R2 (>0.9). 𝑊𝑒𝑖𝑔ℎ𝑡 𝑙𝑜𝑠𝑠 (%) = 1.7108 + 0.159983 𝐴 + 0.556426 𝐵 − 1.14783𝐶 − 0.049168 𝐷 − 0.049168 𝐴𝐵 − 0.01795 𝐴𝐶 − 0.012134 𝐴𝐷+ 0.068283 𝐵𝐶 − 0.019848 𝐵𝐷 + 0.041361 𝐶𝐷 + 0.010383 𝐴T + 0.053426 𝐶T (𝐄𝐪. 𝟒. 𝟐) 𝐹𝑖𝑟𝑚𝑛𝑒𝑠𝑠 (𝑔) = 667.2049 + 1.74936 𝐴 + 79.72565 𝐵 + 13.69218 𝐶 + 2.50254 𝐷 − 0.25209 𝐴𝐷 − 1.21594 𝐵𝐷 − 17.38447𝐵T −−0.675793 𝐶T (𝐄𝐪. 𝟒. 𝟑) Table 4.3. Analysis of Variance (ANOVA) for the impact of pulsed light, storage time, O2 and CO2 concentrations on weight loss and firmness of blueberries (cv. Draper) at 0.5 °C and 90-95% RH Parameter Weight Loss (%) Firmness Type III SS F Value Pr > F Type III SS F Value Pr > F Model 911.66 275.31 < 0.0001 2.09E+06 189.97 < 0.0001*** A-Pulsed Light 22.2 80.45 < 0.0001*** 70.61 0.0513 0.8212 60 B-Time of storage 268.06 971.39 < 0.0001*** 8.77E+05 636.71 < 0.0001*** C-Oxygen concentration 160.42 581.33 < 0.0001*** 7059.49 5.12 0.025* D-Carbon dioxide concentration 38.26 138.63 < 0.0001*** 8799.39 6.39 0.0125* AB 4.69 17 < 0.0001*** - - - AC 13.59 49.26 < 0.0001*** - - - AD 3.59 13.01 0.0005** 3121.42 2.27 0.1343 BC 41.08 148.88 < 0.0001*** 3121.42 22.8 - BD 1.99 7.21 0.0083* - - < 0.0001*** CD 40.14 145.47 < 0.0001*** - - - A² 1.13 4.11 0.0448* - - - B² - - - 7.96E+05 577.77 < 0.0001*** C² 82.75 299.88 < 0.0001*** 1.03E+05 74.95 < 0.0001*** * p < 0.05; ** p < 0.005; *** p < 0.0005. In terms of the PL treatments, previous studies denoted the significant efficacy of PL treatments in the weight loss of blueberries during the storage time (Cao et al., 2017). Likewise, our study on the blueberries treated with PL demonstrated the application of PL with doses of 6 and 9 J cm-2 had a significant decrease in weight loss during 6 weeks of storage. In terms of the firmness of blueberries treated by PL during the storage time, similar results were reported by Rock et al. (2015) and Cao et al. (2019) with no significant effect of PL on the blueberry firmness. Previous research has showed the storage atmosphere had no impact on the blueberry weight loss (Paniagua et al., 2014); nonetheless, our findings showed that 61 applying the lower level of O2 (less than 10kPa) compared to control (O2: 21kPa) could lead to less weight loss during 6 weeks of storage. The different cultivars used in each research is likely to be one of the reasons for the contrast between the results of different studies. 0 1 2 3 4 5 6 0 1 2 3 4 5 6 7 8 9-5 0 5 10 15 Weight Loss (%)A: Pulsed Light (J/cm2)B: Time of storage (Weeks)Factor Coding: ActualWeight Loss (%)0.338775 13.0123X1 = AX2 = BActual FactorsC = 11.25D = 7.751.5 5.4 9.3 13.2 17.1 21 0 1 2 3 4 5 6 7 8 9-5 0 5 10 15 20 Weight Loss (%)A: Pulsed Light (J/cm2)C: Oxygen (kPa)Factor Coding: ActualWeight Loss (%)0.338775 13.0123X1 = AX2 = CActual FactorsB = 6D = 7.750.5 3.4 6.3 9.2 12.1 15 0 1 2 3 4 5 6 7 8 9-5 0 5 10 15 20 Weight Loss (%)A: Pulsed Light (J/cm2)D: Carbon dioxide (kPa)Factor Coding: ActualWeight Loss (%)0.338775 13.0123X1 = AX2 = DActual FactorsB = 6C = 11.251.5 5.4 9.3 13.2 17.1 21 0 1 2 3 4 5 6-5 0 5 10 15 20 Weight Loss (%)B: Time of storage (Weeks)C: Oxygen (kPa)Factor Coding: ActualWeight Loss (%)0.338775 13.0123X1 = BX2 = CActual FactorsA = 4.5D = 7.75b c d a X1= A X2= B Actual Factors C= 11 D= 8 X1= A X2= C Actual Factors B= 6 D= 8 X1= A X2= D Actual Factors B= 6 C= 11 X1= B X2= C Actual Factors A= 4.5 D= 8 62 Figure 4.7. Response surface of weight loss of highbush blueberries (cv. Draper) as affected by (a) time of storage and pulsed light, (b) O2 concentration and pulsed light, (c) CO2 concentration and pulsed light, (d) O2 concentration and time of storage, (e) CO2 concentration and time of storage, (f) CO2 concentration and O2 concentration. In case of firmness, numerous studies showed that high CO2 and low O2 concentrations resulted in reduce firmness. Our research demonstrated that blueberry firmness tended to increase with increasing the CO2 concentration during the four weeks of storage; however, from week 4 onwards, the blueberries started being softer (Figure 4.8). The degradation of primary cell wall components (pectin, cellulose and hemicellulose) can lead to firmness changes during postharvest storage (Liu et al., 2019). The softening in blueberries might happen due to fermentation at high CO2 (Schotsmans et al., 2007; Paniagua et al. 2014). Forney (2009) showed that reducing the firmness varied between cultivars due to anaerobiosis threshold levels. In addition, Falagan et al. (2020) reported that the high CO2 and low O2 0.5 3.4 6.3 9.2 12.1 15 0 1 2 3 4 5 6-5 0 5 10 15 20 Weight Loss (%)B: Time of storage (Weeks)D: Carbon dioxide (kPa)Factor Coding: ActualWeight Loss (%)0.338775 13.0123X1 = BX2 = DActual FactorsA = 4.5C = 11.250.5 3.4 6.3 9.2 12.1 15 1.5 5.4 9.3 13.2 17.1 21-5 0 5 10 15 20 25 Weight Loss (%)C: Oxygen (kPa)D: Carbon dioxide (kPa)Factor Coding: ActualWeight Loss (%)0.338775 13.0123X1 = CX2 = DActual FactorsA = 4.5B = 6f e X1= B X2= D Actual Factors A= 4.5 C= 11 X1= C X2= D Actual Factors A= 4.5 B= 6 63 concentration could suppress polygalacturonase and pectin methylesterase enzymes involved in the catabolism of metabolic reactions of cell wall. Figure 4.8. Response surface of firmness of highbush blueberries (cv. Draper) affected by (a) CO2 concentration and pulsed light, (b) CO2 concentration and time of storage. 4.3.4. Total soluble solids (TSS) and titratable acidity (TA) Analysis of variance of data in Table 4.4 indicated that the quadratic model for TSS and TA was significant (p < 0.05). Regarding TSS, as Table 4.4 shows oxygen concentration, its square, and also carbon dioxide concentration significantly affected the TSS. Moreover, the two-way interaction of all variables (AB, AC, AD, BC, BD, CD) was significant (p < 0.05). For TA, significant impact of time of storage, oxygen concentration and its square on TA were observed. Likewise, AC, BC, BD, and CD presented significant mutual interaction effect on TA. The associated equations for both responses have been given in Equations 4.4 and 4.5. 0.5 3.4 6.3 9.2 12.1 15 0 1 2 3 4 5 6 7 8 9400 500 600 700 800 900 Firmness (g)A: Pulsed Light (J/cm2)D: Carbon dioxide (kPa)Factor Coding: ActualFirmness (g)421.214 878.423X1 = AX2 = DActual FactorsB = 6C = 11.0550.5 3.4 6.3 9.2 12.1 15 0 1 2 3 4 5 6400 500 600 700 800 900 Firmness (g)B: Time of storage (Weeks)D: Carbon dioxide (kPa)Factor Coding: ActualFirmness (g)421.214 878.423X1 = BX2 = DActual FactorsA = 4.5C = 11.055b a X1= A X2= D Actual Factors B= 6 C= 11 X1= B X2= D Actual Factors A= 4.5 C= 11 64 𝑇𝑆𝑆 (%) = 13.5981 + 0.119967 𝐴 + 0.012074 𝐵 − 0.09064 𝐶 + 0.047212 𝐷 − 0.00836 𝐴𝐵 − 0.0056 𝐴𝐶 − 0.00393 𝐴𝐷 + 0.007487 𝐵𝐶− 0.01359 𝐵𝐷 + 0.003927 𝐶𝐷 + 0.010487 𝐵T + 0.004967 𝐶 T (𝑬𝒒. 𝟒. 𝟒) 𝑇𝐴 = 3.85318 − 0.081882 𝐴 − 0.002134 𝐵 + 0.112963 𝐶 + 0.060364 𝐷 + 0.004274 𝐴𝐶 + 0.001649 𝐴𝐷 − 0.0058 𝐵𝐶 − 0.003676 𝐵𝐷− 0.006211 𝐶𝐷 + 0.002562 𝐴T − 0.003808 𝐶T (𝑬𝒒. 𝟒. 𝟓) Table 4.4. Analysis of Variance (ANOVA) for the impact of pulsed light, storage time, O2 and CO2 concentrations on titratable acidity (TA) and total soluble solids (TSS) of blueberries (cv. Draper) at 0.5 °C and 90-95% RH Parameter TA (%) TSS Type III SS F Value Pr > F Type III SS F Value Pr > F Model 9.79 28.74 < 0.0001*** 19.75 16.31 < 0.0001*** A-Pulsed light 0.0067 0.2179 0.6414 0.0027 0.272 0.8693 B-Time of storage 6.58 212.35 < 0.0001*** 0.1876 1.86 0.1748 C-oxygen concentration 0.2834 9.15 0.003** 2 19.81 < 0.0001*** D-carbon dioxide concentration 0.0923 2.98 0.0865 0.6151 6.09 0.0147* AB - - - 0.6995 6.93 0.0093* AC 0.8608 27.79 < 0.0001*** 1.7 16.81 < 0.0001*** AD 0.0752 2.43 0.1214 0.4645 4.6 0.0335* BC 0.757 24.44 < 0.0001*** 1.41 13.93 0.0003** BD 0.1772 5.72 0.0181* 2.59 25.68 < 0.0001*** CD 0.9705 31.33 < 0.0001*** 0.4638 4.6 0.0336* A² 0.0787 2.54 0.1132 - - - B² - - - 0.281 2.78 0.0973 C² 0.4755 15.35 0.0001*** 0.913 9.05 0.0031** * p < 0.05; ** p < 0.005; *** p < 0.0005. As Figure 4.9 shows, the mutual effect of increased CO2 concentration (0.5kPa-15kPa) and O2 concentration (1.5 kPa -21 kPa) and the increase of O2 concentration and the storage time individually resulted in higher TSS. However, with the increase of PL doses from 0 to 9 J cm-2 and CO2 concentration from 0.5 kPa to15 kPa 65 individually, TSS was reduced. In line with our findings, Moreno et al. (2007) denoted that the TSS in irradiated blueberries was lower than control berries after six weeks of the storage. However, Perkins-Veazie et al. (2008) reported UV-C light did not have any significant effect on TSS of blueberries. These variations could be related to cultivars, storage conditions and time of storage. The TSS decreased with the increase of O2 concentration and the storage time which might have been related to rise in the respiration rate; nonetheless the increase of PL doses and oxygen concentration led to decrease TSS. Regarding the CAS, no significant changes were reported in TSS of blueberries in CAS compared to control (Schotsmans et al., 2007). Matityahu et al. (2016) reported that CAS with 2 kPa O2 and 5 kPa CO2 could reduce the respiration rate and sugar break-down in pomegranate fruits which caused the higher TSS in CAS than Regular atmosphere. Moreover, the previous studies reported that the TSS in blueberries generally declined at a faster pace in regular atmosphere storage than in CAS after six weeks of the storage (Schotsmans et al., 2007). 66 0 1 2 3 4 5 6 0 1 2 3 4 5 6 7 8 913 13.5 14 14.5 15 15.5 16 TSS (°Brix)A: Pulsed Light (J/cm2)B: Time of storage (Weeks)Factor Coding: ActualTSS (°Brix )13.1333 15.8X1 = AX2 = BActual FactorsC = 11.055D = 8.041.5 5.4 9.3 13.2 17.1 21 0 1 2 3 4 5 6 7 8 913 13.5 14 14.5 15 15.5 16 TSS (°Brix)A: Pulsed Light (J/cm2)C: Oxygen (kPa)Factor Coding: ActualTSS (°Brix )13.1333 15.8X1 = AX2 = CActual FactorsB = 6D = 8.040.5 3.4 6.3 9.2 12.1 15 0 1 2 3 4 5 6 7 8 913 13.5 14 14.5 15 15.5 16 TSS (°Brix)A: Pulsed Light (J/cm2)D: Carbon dioxide (kPa)Factor Coding: ActualTSS (°Brix )13.1333 15.8X1 = AX2 = DActual FactorsB = 6C = 11.0551.5 5.4 9.3 13.2 17.1 21 0 1 2 3 4 5 613 13.5 14 14.5 15 15.5 16 TSS (°Brix)B: Time of storage (Weeks)C: Oxygen (kPa)Factor Coding: ActualTSS (°Brix )13.1333 15.8X1 = BX2 = CActual FactorsA = 4.5D = 8.040.5 3.4 6.3 9.2 12.1 15 0 1 2 3 4 5 613 13.5 14 14.5 15 15.5 16 TSS (°Brix)B: Time of storage (Weeks)D: Carbon dioxide (kPa)Factor Coding: ActualTSS (°Brix )13.1333 15.8X1 = BX2 = DActual FactorsA = 4.5C = 11.0550.5 3.4 6.3 9.2 12.1 15 1.5 5.4 9.3 13.2 17.1 2113 13.5 14 14.5 15 15.5 16 TSS (°Brix)C: Oxygen (kPa)D: Carbon dioxide (kPa)Factor Coding: ActualTSS (°Brix )13.1333 15.8X1 = CX2 = DActual FactorsA = 4.5B = 6a d c f e b X1= A X2= B Actual Factors C= 11 D= 8 X1= A X2= C Actual Factors B= 6 D= 8 X1= A X2= D Actual Factors B= 6 C= 11 X1= B X2= C Actual Factors A= 4.5 D= 8 X1= B X2= D Actual Factors A= 4.5 C= 11 X1= C X2= D Actual Factors A= 4.5 B= 6 67 Figure 4.9. Response surface of total soluble solids of highbush (TSS) blueberries (cv. Draper) affected by (a) time of storage and pulsed light, (b) O2 concentration and pulsed light, (c) CO2 concentration and pulsed light, (d) O2 concentration and time of storage, (e) CO2 concentration and time of storage, (f) CO2 concentration and O2 concentration. As shown in Figure 4.10, the interaction effects illustrate that TA decreased with increasing storage time and O2 concentration (BC), and also with increasing O2 and CO2 level (CD). However, berries with higher PL treatment and O2 level at 10 kPa reached the higher TA. Our Pl results on TA agree with the finding of Rock et al. (2015) that demonstrated that fresh highbush blueberries treated with different doses of PL did not show any significant changes compared to control groups. Moreover, Perkins-Veazie et al. (2008) reported that 0 to 4 kJ m-2 UV-C treatment did not affect TA, however seven-day storage time showed a slight impact on the treated blueberries. The degradation of organic acids during storage period could lead to a decrease in TA. This result is consistent with previous findings that implied that fruits in CAS with low oxygen storage retained the higher TA content during the storage time than the RA-stored fruits (Ali et al., 2016; Ma et al., 2019). Slower senescence rate and the respiration rate can be two major factors contributing to the higher TAs in CASs. Low O2 and high CO2 concentration during storage period can lower in decarboxylation of organic acids in fruits (i.e. malic acid) which serves as the enzyme substrate in respiration reaction. 68 0 1 2 3 4 5 6 0 1 2 3 4 5 6 7 8 93 3.5 4 4.5 5 TA (%)A: Pulsed Light (J/cm2)B: Time of storage (Weeks)Factor Coding: ActualTA (%)3.59073 4.87417X1 = AX2 = BActual FactorsC = 11.055D = 8.041.5 5.4 9.3 13.2 17.1 21 0 1 2 3 4 5 6 7 8 93 3.5 4 4.5 5 TA (%)A: Pulsed Light (J/cm2)C: Oxygen (kPa)Factor Coding: ActualTA (%)3.59073 4.87417X1 = AX2 = CActual FactorsB = 6D = 8.040.5 3.4 6.3 9.2 12.1 15 0 1 2 3 4 5 6 7 8 93 3.5 4 4.5 5 TA (%)A: Pulsed Light (J/cm2)D: Carbon dioxide (kPa)Factor Coding: ActualTA (%)3.59073 4.87417X1 = AX2 = DActual FactorsB = 6C = 11.0551.5 5.4 9.3 13.2 17.1 21 0 1 2 3 4 5 63 3.5 4 4.5 5 TA (%)B: Time of storage (Weeks)C: Oxygen (kPa)Factor Coding: ActualTA (%)3.59073 4.87417X1 = BX2 = CActual FactorsA = 4.5D = 8.040.5 3.4 6.3 9.2 12.1 15 0 1 2 3 4 5 63 3.5 4 4.5 5 TA (%)B: Time of storage (Weeks)D: Carbon dioxide (kPa)Factor Coding: ActualTA (%)3.59073 4.87417X1 = BX2 = DActual FactorsA = 4.5C = 11.0550.5 3.4 6.3 9.2 12.1 15 1.5 5.4 9.3 13.2 17.1 212.5 3 3.5 4 4.5 5 TA (%)C: Oxygen (kPa)D: Carbon dioxide (kPa)Factor Coding: ActualTA (%)3.59073 4.87417X1 = CX2 = DActual FactorsA = 4.5B = 6b a d c f e X1= A X2= B Actual Factors C= 11 D= 8 X1= A X2= C Actual Factors B= 6 D= 8 X1= A X2= D Actual Factors B= 6 C= 11 X1= B X2= C Actual Factors A= 4.5 D= 8 X1= B X2= D Actual Factors A= 4.5 C= 11 X1= C X2= D Actual Factors A= 4.5 B= 6 69 Figure 4.10. Response surface of total acidity of highbush blueberries (cv. Draper) by plotting; (a) time of storage and pulsed light, (b) O2 concentration and pulsed light, (c) CO2 concentration and pulsed light, (d) O2 concentration and time of storage, (e) CO2 concentration and time of storage, (f) CO2 concentration and O2 concentration. 4.3.5. DPPH free radical scavenging activity As can be seen in Figure 4.11, pulsed light and time of storage individually gave rise to a significant increase (p < 0.05) in the IC50 (decreased in antioxidant activity). In addition, the quadratic effect of PL (A2) and Time of storage (B2) were significant (p < 0.0001). The table 4.5 also shows the interactive significant effect (p < 0.05) of AB, AC, BC, BD, CD. The final model by dropping non-significant variable given in Equation 4.6: 𝐼𝐶50 = 0.545775 + 0.016645𝐴 + 0.036534𝐵 − 0.000913𝐶 − 0.000105𝐷 − 0.001285𝐴𝐵 + 0.000807𝐴𝐶 + 0.000445𝐴𝐷 − 0.001447𝐵𝐶− 0.001948𝐵𝐷 + 0.000241𝐶𝐷 − 0.001771𝐴T + 0.005670𝐵T (𝑬𝒒. 𝟒. 𝟔) Table 4.5. Analysis of Variance (ANOVA) for the impact of pulsed light, storage time, O2 and CO2 concentrations on DPPH free radical scavenging activity of blueberries (cv. Draper) at 0.5 °C and 90-95% RH Parameter IC50 (mg/mL) Type III SS F Value Pr > F Model 1.35 80.42 < 0.0001*** A-Pulsed Light 0.1608 114.84 < 0.0001*** B-Time of storage 0.8695 620.96 < 0.0001*** C-Oxygen concentration 0.0002 0.1539 0.6954 D-Carbon dioxide concentration 0.0033 2.38 0.1250 AB 0.0158 11.27 0.001** AC 0.0311 22.20 < 0.0001*** 70 AD 0.0049 3.50 0.0633 BC 0.0397 28.38 < 0.0001*** BD 0.0404 28.82 < 0.0001*** CD 0.0092 6.55 0.0115** A² 0.0406 29.00 < 0.0001*** B² 0.0834 59.53 < 0.0001*** * p < 0.05; ** p < 0.005; *** p < 0.0005. The interactive effect of time of storage and PL in Figure 4.12 indicates that IC50 increased up to 0.80 mg/mL with increasing doses of PL after six weeks of storage. It also can be seen that even though the increase of CO2 concentration and storage period resulted in IC50 increasing (lower antioxidant activity), a rise in the CO2 concentration led to lower IC50 (higher antioxidant activity) after week 6 compared to the IC50 of the berries at week 6 with lower CO2 level. In the current study, almost all treated samples with PL exhibited lower antioxidant activity than control. It has been previously reported that, depending on the dose of UV-C irradiation and PL doses, the total phenol and anthocyanins could decrease or increase during the storage time which could be related to degradation of phenolics and quinone polymerization (Oms-Oliu et al. 2010; Wiktor et al., 2019). Moreover, our study showed that DPPH radical scavenging activity in all blueberry samples continuously decreased with the increased storage time in all treatments which was in line with the previous research (Ali et al., 2016; Ma et al., 2019). It has been reported that 71 DPPH radical scavenging activity in CAS conditions were higher in litchi fruit after 28 days of storage which could be due to suppressing oxidation of anthocyanins, phenolic compounds and ascorbic acid in CAS fruits (Ali et al., 2016). The reduction of antioxidant activity can be related to enzyme activity changes during the storage time which can impact on phenolic degradation (Selcuk & Erkan, 2015). A: Pulsed Light (J/cm2)0 1 2 3 4 5 6 7 8 9IC50 (mg/ml)0.50.60.70.80.91Factor Coding: ActualActual FactorsA = 4.5B = 6C = 11.055D = 8.04B: Time of storage (Weeks)0 1 2 3 4 5 6IC50 (mg/ml)0.50.60.70.80.91C: Oxygen (kPa)1.5 5.4 9.3 13.2 17.1 21IC50 (mg/ml)0.50.60.70.80.91D: Carbon dioxide (kPa)0.5 3.4 6.3 9.2 12.1 15IC50 (mg/ml)0.50.60.70.80.91a c b d 72 Figure 4.11. Effect of pulsed light (A), time of storage (B), O2 concentration (C), and CO2 concentration (D) on antioxidant activity of highbush blueberries (cv. Draper), where A, C, D are at the center point of the design and B is at week 6. 0 1 2 3 4 5 6 0 1 2 3 4 5 6 7 8 90.5 0.6 0.7 0.8 0.9 1 IC50 (mg/ml)A: Pulsed Light (J/cm2)B: Time of storage (Weeks)Factor Coding: Actual0.5215 0.9059X1 = AX2 = BActual FactorsC = 11.055D = 8.041.5 5.4 9.3 13.2 17.1 21 0 1 2 3 4 5 6 7 8 90.5 0.6 0.7 0.8 0.9 1 IC50 (mg/ml)A: Pulsed Light (J/cm2)C: Oxygen (kPa)Factor Coding: Actual0.5215 0.9059X1 = AX2 = CActual FactorsB = 6D = 8.040.5 3.4 6.3 9.2 12.1 15 0 1 2 3 4 5 6 7 8 90.5 0.6 0.7 0.8 0.9 1 IC50 (mg/ml)A: Pulsed Light (J/cm2)D: Carbon dioxide (kPa)Factor Coding: Actual0.5215 0.9059X1 = AX2 = DActual FactorsB = 6C = 11.0551.5 5.4 9.3 13.2 17.1 21 0 1 2 3 4 5 60.5 0.6 0.7 0.8 0.9 1 IC50 (mg/ml)B: Time of storage (Weeks)C: Oxygen (kPa)Factor Coding: Actual0.5215 0.9059X1 = BX2 = CActual FactorsA = 4.5D = 8.04d b a c X1= A X2= B Actual Factors C= 11 D= 8 X1= A X2= C Actual Factors B= 6 D= 8 X1= A X2= D Actual Factors B= 6 C= 11 X1= B X2= C Actual Factors A= 4.5 D= 8 73 Figure 4.12. Response surface of antioxidant activity of highbush blueberries (cv. Draper) affected by (a) pulsed light and time of storage, (b) O2 concentration and pulsed light, (c) CO2 concentration and pulsed light, (d) O2 concentration and time of storage, (e) CO2 concentration and time of storage, (f) CO2 concentration and O2 concentration. 4.4. Conclusion The results from this study have shown that PL treatments resulted in weight loss reduction in all CO2 and O2 concentrations during six weeks of the storage. However, PL treatments did not demonstrate any significant effects on firmness and rot incidence of blueberries stored in different O2 and CO2 concentrations during the storage period. In case of TSS, TSS gradually increased during the storage time; however, increasing PL doses in the storage with higher CO2 concentration and lower O2 concentration remained almost constant after six weeks. The gradual TA deduction has been observed during six weeks of storage. In addition, PL significantly increased the TA when O2 concentration decreased. Moreover, it has been found that increasing CO2 concentration from 0.5kPa to 15kPa resulted in 0.5 3.4 6.3 9.2 12.1 15 0 1 2 3 4 5 60.5 0.6 0.7 0.8 0.9 1 IC50 (mg/ml)B: Time of storage (Weeks)D: Carbon dioxide (kPa)Factor Coding: Actual0.5215 0.9059X1 = BX2 = DActual FactorsA = 4.5C = 11.0550.5 3.4 6.3 9.2 12.1 15 1.5 5.4 9.3 13.2 17.1 210.5 0.6 0.7 0.8 0.9 1 IC50 (mg/ml)C: Oxygen (kPa)D: Carbon dioxide (kPa)Factor Coding: Actual0.5215 0.9059X1 = CX2 = DActual FactorsA = 4.5B = 6f e X1= B X2= D Actual Factors A= 4,5 C= 11 X1= C X2= D Actual Factors A= 4.5 B= 6 74 higher antioxidant activity; however, increasing PL doses led to decrease in antioxidant activity during storage time. The results further showed the lightness and blueness of the berries increased significantly with increasing the CO2 concentration during six weeks of the storage while applying PL treatment resulted in lower blueness in the storage. The final results suggested that the optimal conditions obtained by Design-Expert software were at 10 kPa CO2 and 8 kPa O2 concentrations with PL doses of 6 and 9 J cm-2 at 0.5°C and RH of 90-95%. This study suggests that the integration of PL treatment and CAS can enhance the storage shelf-life of highbush blueberries to six; it can also positively affect some quality traits (weight loss, rot incidence, TSS, and TA) for fresh consumption. 75 Chapter 5: Conclusion and future directions 5.1. Conclusions In this study, the impact of three PL treatments with doses of 3, 6, and 9 J cm-2 and combination of these three PL treatments and CASs (8 kPa CO2 + 1.5 kPa O2, 8 kPa CO2 + 10 kPa O2, 15 kPa CO2 + 1.5 kPa O2, 15 kPa CO2 + 10 kPa O2) at 0.5°C and RH of 90%-95% on berries quality (color, firmness, weight loss, and rot incidence, TSS, pH, TA, antioxidant activity) and their shelf-life storage were assessed during six weeks of storage. This research found that all CAS and PL treatments showed a positive effect on decreasing the weight loss of the berries. Antioxidant activity of highbush blueberries decreased with enhancement of PL doses however increasing CO2 concentration from 0.5 kPa to 15 kPa increased antioxidant activity. After six weeks, TSS showed less changes with increasing PL doses with higher CO2 concentration and lower O2 concentration after six weeks. Increasing PL doses in the lower O2 concentration storage led to higher TA. The results demonstrated that PL treatments resulted in a decrease in blueness of the blueberries. The findings suggest that the optimum conditions were CO2 (10 kPa) and O2 (8 kPa) concentrations with PL doses of 6 and 9 J cm-2 at 0.5°C and RH of 90-95% achieving the most desirable quality traits after four weeks among the 76 applied treatments, however the quality parameters were still in acceptable range based on the optimization result after six weeks. 5.2. Further Investigation The next step is to analyze the influence of combined PL treatment and CAS on the growth of surrogate-pathogenic strains of blueberries in order to improve safety of fresh blueberries during export transition. In addition, it is also valuable to investigate the integrated effects of pulsed light treatment and CAS on some other blueberries’ nutritional compositions such as total phenolic content, total anthocyanin content, antioxidant enzyme activity, vitamin C, since there has been a growing interest by customers in the nutritional quality of the food produce and minimally processed foods. The results of this research demonstrated that the combination of PL (6 and 9 J cm-2) and CAS (8 kPa CO2+10 kPa O2) technologies can be a potential strategy to improve most quality parameters and shelf-life of highbush blueberries. However, the quality traits of other highbush cultivars (i.e., duck, bluecrop, calypso, elliot) need to be studied. If the quality attributes, and shelf-life of other highbush cultivars were improved, a further step could be a pilot test expanding the experiments in order to seek a valid and scalable initiative for the blueberry industry. 77 Bibliography Aday, M. S., Temizkan, R., Büyükcan, M. B., & Caner, C. (2013). An innovative technique for extending shelf life of strawberry: Ultrasound. LWT-Food Science and Technology, 52(2), 93-101. Agriculture and Agri-Food Canada (July 2020). Statistical Overview of the Canadian Fruit Industry Retrieved November 15, 2021 from https://agriculture.canada.ca/sites/default/files/legacy/pack/pdf/fruit_report_2019-eng.pdf Agüero, M. V., Jagus, R. J., Martín-Belloso, O., & Soliva-Fortuny, R. (2016). Surface decontamination of spinach by intense pulsed light treatments: Impact on quality attributes. Postharvest Biology and Technology, 121, 118-125. Aguiló-Aguayo, I., Charles, F., Renard, C. M., Page, D., & Carlin, F. (2013). Pulsed light effects on surface decontamination, physical qualities and nutritional composition of tomato fruit. Postharvest Biology and Technology, 86, 29-36. Alamar, M. C., Collings, E., Cools, K., and Terry, L. A. (2017). Impact of controlled atmosphere scheduling on strawberry and imported avocado fruit. Postharvest Biol. Technol. 134, 76–86. doi: 10.1016/j.postharvbio.2017. 08.003 Ali, S., Khan, A. S., Malik, A. U., & Shahid, M. (2016). Effect of controlled atmosphere storage on pericarp browning, bioactive compounds and antioxidant enzymes of litchi fruits. Food Chemistry, 206, 18-29. Alsmairat, N., Contreras, C., Hancock, J., Callow, P. & Beaudry, R. (2011). Use of combinations of commercially relevant O2 and CO2 partial pressures to evaluate the sensitivity of nine highbush blueberry fruit cultivars to controlled atmospheres. Hortscience, 46(1), 74-79. Anugu, A.K. (2013). Microbial Inactivation and Allergen Mitigation of Food Matrix by Pulsed Ultraviolet Light. Ph.D. Thesis, University of Florida, Gainesville, FL, USA. Available online: http://ufdc.ufl.edu/UFE0045406/ 00001 (accessed on 8 October 2021). Asen, S., Stewat, R. N., & Korris, K. H. (1972). Co-pigmentation of Anthocyanins in Plan tissues and Its Effect on Color. Phytochemistry, 11, 1139-1144. Bhavya, M. L., & Umesh Hebbar, H. (2017). Pulsed light processing of foods for microbial safety. Food Quality and Safety, 1(3), 187-202. 78 Bialka, K. L., & Demirci, A. (2007). Decontamination of Escherichia coli O157:H7 and Salmonella enterica on blueberries using ozone and pulsed UV-light. Journal of Food Science, 72(9), M391– M396. https://doi.org/10.1111/j.1750-3841.2007.00517. Bialka, K. L., & Demirci, A. (2008). Efficacy of pulsed UV-light for the decontamination of Escherichia coli O157: H7 and Salmonella spp. on raspberries and strawberries. Journal of Food Science, 73(5), M201-M207. Bratsch, A., & Pattison, J. (2009). Specialty crop profile: Blueberries. Publication 438-103. Virginia Cooperative Extension. Briano, R., Giuggioli, N., Girgenti V., & Peano, C. (2015). Biodegradable and compostable film and modified atmosphere packaging in postharvest supply chain of raspberry fruits (cv. Grandeur). J. Food Process. Pres., 39, 2061–2073. Caminiti, I. M., Palgan, I., Noci, F., Muñoz, A., Whyte, P., Cronin, D. A., ... & Lyng, J. G. (2011). The effect of pulsed electric fields (PEF) in combination with high intensity light pulses (HILP) on Escherichia coli inactivation and quality attributes in apple juice. Innovative Food Science & Emerging Technologies, 12(2), 118-123. Cao, X., Huang, R., & Chen, H. (2019). Evaluation of Food Safety and Quality Parameters for Shelf Life Extension of Pulsed Light Treated Strawberries. Journal of Food Science, 84(6), 1494-1500. https://doi.org/10.1111/1750-3841.14613. Cao, X., Huang, R., Chen, H. (2017). Evaluation of pulsed light treatments on inactivation of Salmonella on blueberries and its impact on shelf-life and quality attributes. International Journal of Food Microbiology, 260, 17-26. http://dx.doi.org/10.1016/j.ijfoodmicro.2017.08.012. Charles, F., Guillaume, C., & Gontard, N. (2008). Effect of passive and active modified atmosphere packaging on quality changes of fresh endives. Postharvest Biol Technol. 48(1):22–29. Chea, S., Yu, D. J., Park, J., Oh, H. D., Chung, S. W., & Lee, H. J. (2019). Preharvest β-aminobutyric acid treatment alleviates postharvest deterioration of ‘Bluecrop’ highbush blueberry fruit during refrigerated storage. Scientia Horticulturae, 246, 95–103. https://doi.org/10.1016/j.scienta.2018.10.036. Chiabrando, V., & Giacalone, G. (2011). Shelf-life extension of highbush blueberry using 1-methylcyclopropene stored under air and controlled atmosphere. Food Chem. 126, 1812–1816. https://doi.org/10.1016/j.foodchem.2010.12.032 79 Chu, W., Gao, H., Cao, S., Fang, X., Chen, H., & Xiao, S. (2017). Composition and morphology of cuticular wax in blueberry (Vaccinium spp.) fruits. Food chemistry, 219, 436-442. Doving, A., Mage, F. & Vestrheim, S. (2005). Methods for testing strawberry fruit firmness: a review. Small Fruit Review 4, 11–34. https://doi.org/10.1080/090647102320260035. Donsì, F., Marchese, E., Maresca, P., Pataro, G., Vu, K. D., Salmieri, S., ... & Ferrari, G. (2015). Green beans preservation by combination of a modified chitosan based-coating containing nanoemulsion of mandarin essential oil with high pressure or pulsed light processing. Postharvest Biology and Technology, 106, 21-32. Duan, J., Wu, R., Strik, B. C., & Zhao, Y. (2011). Effect of edible coatings on the quality of fresh blueberries (Duke and Elliott) under commercial storage conditions. Postharvest biology and technology, 59(1), 71-79. Duarte-Molina, F., Gomez, P. L., Castro, M. A., & Alzamora, S. M. (2016). Storage quality of strawberry fruit treated by pulsed light: Fungal decay, water loss and mechanical properties. Innovative Food Science & Emerging Technologies, 34, 267–274. https://doi.org/10.1016/j.ifset.2016.01.019. Elmnasser, N., Guillou, S., Leroi, F., Orange, N., Bakhrouf, A., & Federighi, M. (2007). Pulsed-light system as a novel food decontamination technology: A review. Canadian Journal of Microbiology 53: 813–821. https://doi.org/10.1139/week 07-042. Falagán, N., Miclo, T., & Terry, L. A. (2020). Graduated controlled atmosphere: a novel approach to increase “Duke” blueberry storage life. Frontiers in plant science, 11, 221. Falagán, N., Miclo, T., & Terry, L. A. (2020). Graduated controlled atmosphere: a novel approach to increase “Duke” blueberry storage life. Frontiers in plant science, 11, 221. Ferrario, M. I., & Guerrero, S. N. (2018). Inactivation of Alicyclobacillus acidoterrestris ATCC 49025 spores in apple juice by pulsed light. Influence of initial contamination and required reduction levels. Revista Argentina de microbiologia, 50(1), 3-11. Ferrario, M., Alzamora, S. M., & Guerrero, S. (2013). Inactivation kinetics of some microorganisms in apple, melon, orange and strawberry juices by high intensity light pulses. Journal of Food Engineering, 118(3), 302-311. Ferrario, M., Alzamora, S. M., & Guerrero, S. (2015a). Study of pulsed light inactivation and growth dynamics during storage of E scherichia coli ATCC 35218, L isteria innocua ATCC 33090, S almonella E nteritidis MA 44 and S accharomyces cerevisiae KE 162 and native flora in apple, orange and strawberry juices. International Journal of Food Science & Technology, 50(11), 2498-2507. 80 Ferrario, M., Alzamora, S. M., Guerrero, S. (2015b). Study of the inactivation of spoilage microorganisms in apple juice by pulsed light and ultrasound. Food Microbiology 46: 635–642. Forney, C. F. (2008). Postharvest issues in blueberry and cranberry and methods to improve market-life. In IX International Vaccinium Symposium, 810, 785-798. Gallagher, M. S., Mahajan, P.V. (Eds.) (2011). The stability and shelf life of fruit and vegetables. In: Food and beverage stability and shelf life, Cambridge, UK: Woodhead Publishing Ltd. 641-656. García-Gómez, B. E., Salazar, J. A., Nicolás-Almansa, M., Razi, M., Rubio, M., Ruiz, D., & Martínez-Gómez, P. (2021). Molecular bases of fruit quality in prunus species: an integrated genomic, transcriptomic, and metabolic review with a breeding perspective. International Journal of Molecular Sciences, 22(1), 333. Gomez-Lopez, V. M., Devileghere, F., Bonduelle, V. & Debevere, J. (2005). Intense light pulses decontamination of minimally processed vegetables and their shelf-life. International Journal of Food Microbiology 103(1): 79–89. Gomez, P. L., Garcia-Loredo, A., Nieto, A., Salvatori, D. M., Guerrero, S., & Alzamora, S. M. (2012). Effect of pulsed light combined with an antibrowning pretreatment on quality of fresh cut apple. Innovative Food Science & Emerging Technologies, 16, 102–112. https://doi.org/10.1016/j.ijfoodmicro.2004.11.028. Gómez, P. L., Welti-Chanes, J., & Alzamora, S. M. (2011). Hurdle technology in fruit processing. Annual Review of Food Science and Technology, 2, 447-465. Gonzalez-Villagra, J., Marjorie, R. D., Alberdi, M., Acevedo, P., Loyola, R., Tighe-Neira, R., ... & Inostroza-Blancheteau, C. (2020). Solar UV irradiation effects on photosynthetic performance, biochemical markers, and gene expression in highbush blueberry (Vaccinium corymbosum L.) cultivars. Scientia Horticulturae, 259, 108816. Guimaraes, I. C., Menezes, E. G. T., De Abreu, P. S., Rodrigues, A. C., Borges, P. R. S., Batista, L. R., Cirilo, M. A., & Lima, L. C. O. (2013). Physicochemical and microbiological quality of raspberries (Rubus idaeus) treated with different doses of gamma irradiation. Food Science and Technology, 33, 316–322. https://doi.org/10.1590/S0101-20612013005000040. Hancock, J., Callow, P., Serce, S., Hanson, E., & Beaudry, R. (2008). Effect of cultivar, controlled atmosphere storage, and fruit ripeness on the long-term storage of highbush blueberries. HortTechnology, 18, 199–205. https://doi.org/10.21273/HORTTECH.18.2.199. Harb, J., & Streif, J. (2004). Controlled atmosphere storage of highbush blueberries cv. ‘Duke’ Eur. J. Hort. Sci., 69, 66-72. 81 Huang, Y., & Chen, H. (2014). A novel water-assisted pulsed light processing for decontamination of blueberries. Food Microbiology, 40, 1–8. https://doi.org/10.1016/j.fm.2013.11.017. Huang, Y., & Chen, H. (2015). Inactivation of Escherichia coli O157: H7, Salmonella and human norovirus surrogate on artificially contaminated strawberries and raspberries by water-assisted pulsed light treatment. Food Research International, 72, 1-7. Huang, Y., Ye, M., Cao, X., Chen, H. (2017). Pulsed light inactivation of murine norovirus, Tulane virus, Escherichia coli O157:H7 and Salmonella in suspension and on berry surfaces. Food Microbiology, 61: 1–4. https://doi.org/10.1016/j.fm.2016.08.001. Hwang, H. J., Cheigh, C. I., & Chung, M. S. (2015). Relationship between optical properties of beverages and microbial inactivation by intense pulsed light. Innovative Food Science & Emerging Technologies, 31, 91-96. Ignat, A., Manzocco, L., Maifreni, M., Bartolomeoli, I., & Nicoli, M. C. (2014). Surface decontamination of fresh-cut apple by pulsed light: effects on structure, colour and sensory properties. Postharvest Biology and Technology, 91, 122-127. John, D., & Ramaswamy, H. S. (2018). Pulsed light technology to enhance food safety and quality: a mini-review. Current Opinion in Food Science, 23, 70-79. Koort, A., Moor, U., Põldma, P., Kaiser, C., & Starast, M. (2018). Comparison of regular atmospheric storage versus modified atmospheric packaging on postharvest quality of organically grown lowbush and half-highbush blueberries. Sustainability, 10(11), 3916. Kramer, B., Wunderlich, J., & Muranyi, P. (2015). Pulsed light decontamination of endive salad and mung bean sprouts and impact on color and respiration activity. Journal of food protection, 78(2), 340-348. Kramer, B., Wunderlich, J., & Muranyi, P. (2017). Recent findings in pulsed light disinfection. Journal of Applied Microbiology, 122(4), 830-856. Krupa, T., & Tomala, K. (2007). Antioxidant capacity, anthocyanin content profile in ‘Bluecrop’ blueberry fruit Veg. Crops Res. Bull., 66, 129-141. Kurek, M., Benbettaieb, N., Ščetar, M., Chaudy, E., Repajić, M., Klepac, D., ... & Galić, K. (2021). Characterization of Food Packaging Films with Blackcurrant Fruit Waste as a Source of Antioxidant and Color Sensing Intelligent Material. Molecules, 26(9), 2569. 82 Leng, J., Mukhopadhyay, S., Sokorai, K., Ukuku, D. O., Fan, X., Olanya, M., & Juneja, V. (2020). Inactivation of Salmonella in cherry tomato stem scars and quality preservation by pulsed light treatment and antimicrobial wash. Food Control, 110, 107005. Liu, B., Wang, K., Shu, X., Liang, J., Fan, X., & Sun, L. (2019). Changes in fruit firmness, quality traits and cell wall constituents of two highbush blueberries (Vaccinium corymbosum L.) during postharvest cold storage. Scientia Horticulturae, 246, 557-562. Loaharanu, P. (2003). Irradiated foods. (5th ed.). New York: American Council of Science and Health; 50pp. Luksiene, Z., Buchovec, I., Kairyte, K., Paskeviciute, E., & Viskelis, P. (2012). High-power pulsed light for microbial decontamination of some fruits and vegetables with different surfaces. J Food Agric Environ, 10(3&4), 162-167. Ma, Y., Li, S., Yin, X., Xing, Y., Lin, H., Xu, Q., ... & Chen, C. (2019). Effects of controlled atmosphere on the storage quality and aroma compounds of lemon fruits using the designed automatic control apparatus. BioMed research international, 2019. https://doi.org/10.1155/2019/6917147. Maftei, N. A., Ramos-Villarroel, A. Y., Nicolau, A. I., Martín-Belloso, O., & Soliva-Fortuny, R. (2014). Influence of processing parameters on the pulsed-light inactivation of Penicillium expansum in apple juice. Food Control, 41, 27-31. Mandal, R., & Pratap-Singh, A. (2021). Characterization of continuous-flow pulsed UV light reactors for processing of liquid foods in annular tube and coiled tube configurations using actinometry and computational fluid dynamics. Journal of Food Engineering, 304, 110590. https://doi.org/10.3390/app10103606. Mandal, R., Mohammadi, X., Wiktor, A., Singh, A., & Pratap-Singh, A. (2020). Applications of pulsed light decontamination technology in food processing: an overview. Applied Sciences, 10(10), 3606. Marquenie, D., Michiels, C. W., Van Impe, J. F., Schrevens, E., & Nicolai, B. N. (2003). Pulsed white light in combination with UV-C and heat to reduce storage rot of strawberry. Postharvest Biology and Technology, 28(3), 455–461. https://doi.org/10.1016/S0925-5214(02)00214-4. Matiacevich, S., Celis Cofré, D., Silva, P., Enrione, J., & Osorio, F. (2013). Quality parameters of six cultivars of blueberry using computer vision. International Journal of Food Science, 2013. Matityahu, I., Marciano, P., Holland, D., Ben-Arie, R., & Amir, R. (2016). Differential effects of regular and controlled atmosphere storage on the quality of three cultivars of pomegranate (Punica granatum L.). Postharvest Biology and Technology, 115, 132-141. 83 Michalska, A., & Lysiak, G. (2015). Bioactive compounds of blueberries: post-harvest factors influencing the nutritional value of products. International journal of molecular sciences, 16(8), 18642-18663. Moggia Lucchini, C., Beaudry, R. M., Retamales, J. B., & Lobos, G. A. (2017). Variation in the impact of stem scar and cuticle on water loss in highbush blueberry fruit argue for the use of water permeance as a selection criterion in breeding. Postharvest Biology and Technology, 132, p. 88-96. Moggia, C., Lobos, G.A., Retamales, J.B. (2014). Modified atmosphere packaging in blueberries: Effect of harvest time and moment of bag sealing. Acta Hortic. 1017, 153–158. Moreira, M. R., Álvarez, M. V., Martín-Belloso, O., Soliva-Fortuny, R. (2017). Effects of pulsed light treatments and pectin edible coatings on the quality of fresh-cut apples: A hurdle technology approach. Journal of the Science of Food and Agriculture 97: 261–268. Moreno, M., Castell-Perez, M., Gomes, C., Da Silva, P., & Moreira, R. (2007). Quality of Electron Beam Irradiation of Blueberries at Medium Dose Levels (1.0 - 3.2kGy). LWT-Food Science Technology, 40(7), 1123-1132. http://dx.doi.org/10.1016/j.lwt.2006.08.012. Mullan, M., & McDowell, D. (2003). 10 Modified atmosphere packaging. Am. Soc. Test. Mater., 303. Muñoz, A., Palgan, I., Noci, F., Morgan, D. J., Cronin, D. A., Whyte, P., & Lyng, J. G. (2011). Combinations of high intensity light pulses and thermosonication for the inactivation of Escherichia coli in orange juice. Food microbiology, 28(6), 1200-1204. Nguyen, C. T. T., Kim, J., Yoo, K. S., Lim, S. Lee, E. J.2014. Effect of prestorage UV-A, -B, and -C radiation on fruit quality and anthocyanin of ’Duke’ blueberries during cold storage. Journal of Agricultural and Food Chemesrty, 62, 12144-12151. https://doi.org/10.1021/jf504366x. Nicorescu, I., Nguyen, B., Moreau-Ferret, M., Agoulon, A., Chevalier, S., & Orange, N. (2013). Pulsed light inactivation of Bacillus subtilis vegetative cells in suspensions and spices. Food Control, 31(1), 151-157. Oms-Oliu, G., Aguiló-Aguayo, I., Martín-Belloso, O., & Soliva-Fortuny, R. (2010). Effects of pulsed light treatments on quality and antioxidant properties of fresh-cut mushrooms (Agaricus bisporus). Postharvest biology and technology, 56, 216–222. https://doi.org/10.1016/j.postharvbio.2009.12.011. Palgan, I., Caminiti, I. M., Muñoz, A., Noci, F., Whyte, P., Morgan, D. J., ... & Lyng, J. G. (2011). Effectiveness of high intensity light pulses (HILP) treatments for the control of Escherichia coli 84 and Listeria innocua in apple juice, orange juice and milk. Food microbiology, 28(1), 14-20. https://doi.org/10.1016/j.fm.2010.07.023. Paniagua Gonzalez, A. C. (2012). M.Sc. Dissertation, Influence of temperature management deficiencies during postharvest on the quality of sea exported blueberries, Massey University, Palmerston North, New Zealand. Paniagua, A. C. East, A. R., Heyes, J. A. (2014) Interaction of temperature control deficiencies and atmosphere conditions during blueberry storage on quality outcomes. Postharvest Biology and Technology, 95, 50–59. Pataro, G., Sinik, M., Capitoli, M. M., Donsì, G., & Ferrari, G. (2015). The influence of post-harvest UV-C and pulsed light treatments on quality and antioxidant properties of tomato fruits during storage. Innovative Food Science & Emerging Technologies, 30, 103-111. Perkins-Veazie, P. (2016). Blueberry. In: Gross, K.C., Wang, C.Y., Saltveit, M. (Eds.), The commercial storage of fruits, vegetables, and florist and nursery stocks. Agriculture handbook 66. USDA, ARS, Beltsville. https://doi.org/10.1016/j.postharvbio.2014.04.006. Perkins-Veazie, P., Collins, J. K., Howard, L. (2008). Blueberry fruit response to postharvest application of ultraviolet radiation. Postharvest Biology and Technology, 47, 280–285. Pico, J., Xu, k., Guo, M., Mohamedshah, Z., Ferruzzi, M. G., & Martinez, M. M. 2019. Manufacturing the ultimate green banana flour: Impact of drying and extrusion on phenolic profile and starch bio-accessibility, Food Chemistry, 297, 124990. https://doi.org/10.1016/j.foodchem.2019.124990. Pollock, A. M., Singh, A. P., Ramaswamy, H. S., & Ngadi, M. O. (2017). Pulsed light destruction kinetics of L. monocytogenes. LWT, 84, 114-121. Ramos-Villarroel, A. Y., Aron-Maftei, N., Martín-Belloso, O., & Soliva-Fortuny, R. (2012a). The role of pulsed light spectral distribution in the inactivation of Escherichia coli and Listeria innocua on fresh-cut mushrooms. Food Control, 24(1-2), 206-213. Ramos-Villarroel, A. Y., Aron-Maftei, N., Martín-Belloso, O., & Soliva-Fortuny, R. (2012b). Influence of spectral distribution on bacterial inactivation and quality changes of fresh-cut watermelon treated with intense light pulses. Postharvest Biology and Technology, 69, 32-39. Ramos-Villarroel, A. Y., Martín-Belloso, O., & Soliva-Fortuny, R. (2011). Bacterial inactivation and quality changes in fresh-cut avocado treated with intense light pulses. European Food Research and Technology, 233(3), 395-402. 85 Ramos-Villarroel, A. Y., Martín-Belloso, O., Soliva-Fortuny, R. (2015). Combined effects of malic acid dip and pulsed light treatments on the inactivation of Listeria innocua and Escherichia coli on fresh-cut produce. Food Control 52: 112–118. Retamales, J. B., & Hancock, J. F. (2012). Blueberries (Vol. 21). In: Crop production science in horticulture. Wallingford, UK: CAB International. Rock, C., Guner, S., Yang, W., Gu, L., Percival, S., & Salcido, E. (2015). Enhanced Antioxidant Capacity of Fresh Blueberries by Pulsed Light Treatment. J. Food Res., 4(5): 89–97. http://dx.doi.org/10.5539/jfr.v4n5p89. Rowan, N. J. (2019). Pulsed light as an emerging technology to cause disruption for food and adjacent industries–Quo vadis?. Trends in food science & technology, 88, 316-332. Salinas-Roca, B., Soliva-Fortuny, R., Welti-Chanes, J., & Martín-Belloso, O. (2016). Combined effect of pulsed light, edible coating and malic acid dipping to improve fresh-cut mango safety and quality. Food Control, 66, 190-197. Sauer, A., & Moraru, C. I. (2009). Inactivation of Escherichia coli ATCC 25922 and Escherichia coli O157: H7 in apple juice and apple cider, using pulsed light treatment. Journal of Food Protection, 72(5), 937-944. Schotsmans, W., Molan, A., & MacKay, B. (2007). Controlled atmosphere storage of rabbiteye blueberries enhances postharvest quality aspects Postharvest Biol. Technol., 44, 277-285. Schreiner, M., Martínez-Abaigar, J., Glaab, J., & Jansen, M. (2014). UV-B induced secondary plant metabolites: potential benefits for plant and human health. Optik & Photonik, 9(2), 34-37. Segundo, C., Roman, L., Gomez, M., & Martínez, M. M. (2016). Mechanically fractionated flour isolated from green bananas (M. cavendishii var.nanica ) as a tool to increase the dietary fibre and phytochemical bioactivity of layer and sponge cakes. Food Chemistry, 219, 240–248. https://doi.org/10.1016/j.foodchem.2016.09.143. Selcuk, N., & Erkan, M. (2015). The effects of modified and palliflex controlled atmosphere storage on postharvest quality and composition of ‘Istanbul’medlar fruit. Postharvest biology and technology, 99, 9-19. Skrovankova, S., Sumczynski, D., Mlcek, J., Jurikova, T. & Sochor, J. (2015). Bioactive compounds and antioxidant activity in different types of berries. International Journal of Molecular Sciences, 16, 24673–24706. https://doi.org/10.3390/ijms161024673. 86 Tadapaneni, R. K., Daryaei, H., Krishnamurthy, K., Edirisinghe, I., & Burton-Freeman, B. M. (2014). High-pressure processing of berry and other fruit products: Implications for bioactive compounds and food safety. Journal of agricultural and food chemistry, 62(18), 3877-3885. Tano, K., A. Kamenan, Arul, J. (2005). Respiration and transpiration characteristics of selected fresh fruits and vegetables. Agronomie africaine 17(2), 103- 115. DOI: 10.4314/aga.v17i2.1662. Uesugi, A. R., Moraru, C. I. (2009). Reduction of listeria on ready-to-eat sausages after exposure to a combination of pulsed light and nisin. Journal of Food Protection 72: 347–353. US Department of Agriculture (USDA), Food Data: Blueberries, raw (April 2019), Retrieved November 9, 2021 from: https://fdc.nal.usda.gov/fdc-app.html#/food-details/171711/nutrients USDA foreign agricultural service (2017). Highbush blueberry production in Canada. Retrieved July 5, 2021 from: https://apps.fas.usda.gov/newgainapi/api/report/downloadreportbyfilename?filename=High%20Bush%20Blueberry%20Production%20in%20Canada_Ottawa_Canada_12-29-2017.pdf Valdivia Nájar, C. G., Martín Belloso, O., & Soliva-Fortuny, R. (2018). Impact of pulsed light treatments and storage time on the texture quality of fresh-cut tomatoes. Innovative Food Science & Emerging Technologies, 45, 29-35. https://doi.org/10.1016/j.ifset.2017.08.007. Valdivia-Nájar, C. G., Martín-Belloso, O., Giner-Seguí, J., & Soliva-Fortuny, R. (2017). Modeling the inactivation of Listeria innocua and Escherichia coli in fresh-cut tomato treated with pulsed light. Food and Bioprocess Technology, 10(2), 266-274. Waghmare, R. B., & Annapure, U. S. (2018). Integrated effect of radiation processing and modified atmosphere packaging (MAP) on shelf life of fresh fig. Journal of food science and technology, 55(6), 1993-2002. Wang, C., Gao, Y., Tao, Y., Wu, X., & Zhibo, C. (2017). Influence of γ- irradiation on the reactive-oxygen metabolism of blueberry fruit during cold storage. Innovative Food Science & Emerging Technologies, 41, 397–403. https://doi.org/10.1016/j.ifset.2017.04.007. Wekhof, A., Trompeter, F. J., & Franken, O. (2001, June). Pulsed UV disintegration (PUVD): a new sterilisation mechanism for packaging and broad medical-hospital applications. In The first international conference on ultraviolet technologies (p. 15). Wiktor, A., Mandal, R., Singh, A., & Pratap-Singh, A. (2019). Pulsed Light treatment below a Critical Fluence (3.82 J/cm2) minimizes photo-degradation and browning of a model Phenolic (Gallic Acid) Solution [A]. doi:http://dx.doi.org/10.14288/1.0380957. 87 Wills, R. B. H., McGlasson, W. B. & Joyce, D. C. (2007). Postharvest: an introduction to the physiology and handling of fruit, vegetables and ornamentals (5th ed.). Sydney University of New South Wales Press. Xu, W., & Wu, C. (2016). The impact of pulsed light on decontamination, quality, and bacterial attachment of fresh raspberries. Food Microbiology, 57, 135-143. Yan, Y., Song, C., Falginella, L., & Castellarin, S. D. (2020). Day Temperature Has a Stronger Effect Than Night Temperature on Anthocyanin and Flavonol Accumulation in ‘Merlot’ (Vitis vinifera L.) Grapes During Ripening. Front. Plant Sci. 11:1095. https://doi.org/10.3389/fpls.2020.01095.
Thesis/Dissertation
eng
Food Science
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Pratap-Singh, Anubhav
Application of pulsed light and controlled atmosphere storage for extension of post-harvest quality and shelf-life of highbush blueberries (cv. Draper)
Text