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UBC Theses and Dissertations

Sensory evaluation and volatile compound analysis of strawberry fruit with and without modified atmosphere packaging (MAP) Shamaila, Mawele M.


In the last few years, packaging of horticultural commodities in polymeric film pouches as means of extending their shelf life has expanded at the retail level. The modified atmospheres in commodity-containing pouches which consist of elevated levels of C02 and reduced levels of 02 may influence the quality attributes of the edible tissues. In this study, strawberries were stored at 1°C for 10 days under modified atmosphere package (MAP) conditions in high barrier film pouches flushed with either carbon dioxide (100% C02) , mixed gas (11% C02 + 11% 02 + N2 as balance) or air to assess relationships between sensory attributes, chemical parameters and gas chromatographic data by applying multivariate statistical techniques. The first two principal components which accounted for 92% of variance indicated that the changes in sensory quality of strawberries evaluated by quantitative descriptive analysis (QDA) were mainly a contrast of desirable (strawberry odor, texture and sweetness) against undesirable attributes (off-odor, fermented odor, musty odor and bitterness). Strawberries stored for only a few days were associated with desirable attributes. Deteriorated samples due to treatment and/or storage time as a result of changes in C02 and 02 were associated more with undesirable attributes. There were statistical differences in nearly all attributes studied between different treatments over storage time. Packaged strawberries treated with air retained their desirable attributes for longer storage time than those treated with mixed gas or carbon n dioxide, while unpackaged fruit developed fungal growth after 6 days of storage at 1°C. As the storage time increased, the ethanol concentration increased in strawberries packaged in the different gases, with mixed gas treated samples showing the highest amounts. Significant correlations were obtained between desirable and undesirable attributes, and with soluble solids and ethanol content. Most of the fifty volatile compounds extracted by a dynamic headspace purge-and-trap (DHPT) technique and adsorbed onto Tenax GC were identified by gas chromatography/mass spectrometry (GC/MS) as esters. Total relative amounts of volatile compounds and total amounts of butanoates from strawberries stored under different MAP conditions were much lower than for unpackaged strawberries. Significant correlations were found between odor attribute values and volatile compounds such as methyl butanoate, 1-methylethyl hexanoate, 3,7 dimethyl-1,6-octadien-3-ol and ethyl heptanoate. Multiple regression of 25 selected volatile compounds with the odor attribute values accounted for up to 70% of the variation, while stepwise regression selected between 6 and 9 variables with up to 67% of variance being explained. The data for 25 selected volatile compounds for untreated and gas-treated strawberries were subjected to canonical variate analysis (CVA). Samples held in air, mixed gas and the unpackaged fruit and strawberries evaluated at day 0 were all initially separated from strawberries held in carbon dioxide. After 10 days in storage, all MAP strawberries were classified in close iii proximity, with the indication that quality attribute scores were low. This was attributed to elevated C02 and reduced 02 levels in packages containing the strawberries. Assessment of volatile compound data by CVA could be valuable in monitoring quality of strawberries and supplementing sensory evaluation of the fruit stored under various conditions. In a separate experiment, 6 strawberry cultivars, 'Mrak', 'Ranier', 'Redcrest', 'Selva', 'Sumas' and 'Totem' were compared for sensory and chemical properties, and selected volatile compounds. 'Redcrest' had the most intense sourness, lowest pH, high titratable acidity and lowest overall fruit quality. Twodimensional partitioning (TDP) showed that the overall quality of the strawberries was primarily dependent on odor and sweetness level. Cultivars differed in all orthogonal variates except odor. While judges could not detect odor differences, the total relative amounts of volatile compounds were greatest for 'Mrak' and 'Selva'. Canonical variate analysis (CVA) based on volatile compounds classified the cultivars according to the region in which they were bred.

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