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2009 Thermal Processing Part 1

2009 Thermal Processing Part 1 - Unit Processes Heat...

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Unit Processes: Heat
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Thermal Processing as a Means of Preserving Foods Major Objective: Render the food microbially “safe” while maintaining other quality attributes
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Objectives of thermal processing 1. Blanching : Inactivate endogenous enzymes in fruits, veg. prior to freezing; typically 100 C, <1 min 1. Pasteurization : Kill disease causing organisms; 63 C (145 F), 30 min or 72 C (161 F), 15 sec 1. Commercial sterility : Kill all disease and spoilage microorganisms capable of growing in the product 4. Sterility : Kill all microorganisms
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Thermal processing of foods: Ultrapasteurization Conventional pasteurization: 160 F (71 C) for 15 seconds Shelf-life (milk): 10-14 days (unopened) Ultrapasteurization: 285 F (140 C) for 2 seconds Shelf-life (milk): 6 months (unopened)
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Effects of HEAT on Food Quality Beneficial effects of heat treatment: Kills microorganisms that cause * spoilage * disease Inactivates spoilage enzymes , e.g. proteases lipases lipoxygenases polyphenoloxidase Improves texture of some foods * meats (red meats, poultry) * fibrous plant foods Improves digestibility of some foods
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Detrimental effects of heat treatment: Nutrient loss Excessive softening (some plant foods) Destroys or forms pigments pheophytin from chlorophyll Browning reactions e.g. evaporated milk Catalyzes flavor changes
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