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UBC Theses and Dissertations

Design, development, and validation of continuous-flow pulsed UV light systems for liquid food processing Mandal, Ronit


Pulsed UV light (PL) is a non-thermal food preservation method that employs high-intensity short-duration pulses of polychromatic light (200-1200 nm) to inactivate microorganisms while having minimal effects on nutrients and sensory acceptability. PL is an excellent decontamination technology for solid foods. However, for liquids, parameters like clarity, turbidity, UV transmissivity govern the PL efficacy. Therefore, my work is focused on developing an understanding of PL processing using modeling and computational simulation of different liquids. The PL system used consists of two different quartz reactors (annular [AT] and coiled tube [CT]) with a cylindrical lamp at the axis. The 3-D light energy distribution was modeled using water, model liquid foods (water + red/green dye), and skim milk around the lamp to predict lamp energy at any point in space around the lamp. Liquids were treated in the reactors at various flow rates (14-75 L/h) and pulse frequency (1-5 Hz) after inoculation with Escherichia coli ATCC 29055, Listeria innocua ATCC 33090 and Clostridium sporogenes ATCC 7955. A batch collimation experiment was done to ascertain UV dosage for microbial inactivation in the liquids. The inactivation was in the order: water > water + red dye > water + green dye > milk. Then, milk samples (0%, 1%, 2% and 3.25% fat) were treated under the same conditions and analyzed for microbial inactivation, pH, colour, vitamin B2 and C content, lipid, and protein oxidation. Up to 4 logs reduction of microorganisms were obtained for milk. The pH of the treated samples was similar to the control. The colour parameter b* decreased as treatment intensified, while vitamin B2 and C decreased significantly. There was significant lipid oxidation and protein oxidation. Red grape and watermelon juice were treated under the same conditions and analyzed for microbial inactivation, pH, colour, total phenolics, antioxidant capacity, lycopene, and anthocyanin contents. While there was complete inactivation (>7 logs) of microbes in juices, there were minimal effects on colour and pH; but the phenolics, antioxidants, and anthocyanins were affected greatly. The results of this study will inform the food industry on how to use this technology effectively.

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