2009 Thermal Processing & Preservation

2009 Thermal Processing & Preservation - Unit...

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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 formation
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Microbial Safety Nutritional Quality Process Time & Temperature Outcome of Process Inverse Relationship Between Desired Outcome & Thermal Process Severity
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Heat Preservation How do we resolve the opposing goals of preserving foods for later use and the detrimental effects that heat can have on flavor and nutritional quality?
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Susceptibility of various food components to heat can be compared using " D " values     "D T "  =  time  to achieve  1 log (10-fold) reduction  in  concentration   (value) of a component  at a specified temperature  (T)                    (reflects the   rate  of rxn  or  slope   of the conc. vs time curve)       "D 121  "  =  minutes  at  121¡ C  to achieve  a 10-fold reduction in         concentration  (value) of a component    
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Rate of thermal destruction of vitamins and bacteria: log function Time D D T Concentration (log scale) 1 log reduction
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Number of surviving cells Time 118 C 115 C 110 C 121 C 125 C
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2009 Thermal Processing &amp; Preservation - Unit...

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