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2009 Low Temp Preservation of Foods

2009 Low Temp Preservation of Foods - The origin of...

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The origin of refrigeration? (and who said research was easy !?)
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Low Temperature Preservation of Foods Refrigeration Freezing Objectives of refrigeration / freezing: 1. Slow microbial growth     Microorganisms can cause:       Flavor, odor changes       Appearance  changes  (s ecrete pigments  or  enzymes           which deg rade color)       Texture ch anges  (s ecretion of enzymes   which break          down proteins , fibers )       Pathogenic conditions     2.  Slow or s top enzymatic / chemical reactions    
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Refrigeration Preservation of Foods A. Refrigeration of Meats, Poultry, Fish Optimum temp = -1 to + 2¡ C (just above freezing pt) Major objective: prevention of microbial growth     B.  Refrigeration of Plant Foods         More problematic than mea ts       Challenge :    Plant foods  are  alive   (unlike meats )                    Quality depends  on  management  of certain              biochemical proces s es  of living tis s ues  
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After harvest, many physiological processes continue : 1. Respiration O 2 organic molecules energy (ATP) + CO 2 + heat (starch) 2. Synthesis of hormones, pigments, enzym es 3. Changes in cell wall structure Enzymatic degrada tion of pectins, cellulose may lead to softening
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Texture of fruits & vegetables     Important q uality attributes:   Crispness                   Succulence                 Crunchiness   Texture of fresh plant foods due to two factors : 1. Structure and condition of cell walls Thickness and strength Adhesion to adjacent cells 2. Cell "turgor pressure" Water pressure inside cell >> outside Because solute conc. inside > outside, water moves from outside to inside ( osmotic pressure ) Maintenance of turgor pressure requires: * intact cell membranes, cell walls * energy (ATP)
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Goals of refrigeration of plant foods: * Slow rate of respiration, other biochemical processes, prolong shelf life , yet * Allow sufficient energy production to maintain essential cellular processes Decr. temp. Decr. respiration rate Increase storage life
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