Freezing

• The freezing is the process of lowering the temperature below freezing point of water with the formation of ice in the product
• Phenomena during freezing process are freezing point depression, ice formation, freeze concentration, recrystallisation, and freezer burn
• Effects of freezing on threat factors are Chemical reaction rate, Reaction rate of enzymes, Microorganisms
• Freezing methods base on products and equipments
• Meat, Poultry and fish should be frozen after rigour. If not they might shrink, becomes elastic, loss of moisture
• Damaging factor during frozen storage is fat oxidation by enzyme lipase and phospholipase (acts to release free fatty acids that will be oxidised)
• Fish damage; protein degradation due to increased salt concentration and pH changes
• Fish damage; degradation by reaction with lipids and the result of lipid oxidation produces elastic fish tissues
• Decomposition of trimethylamine oxide (TMAO) produces dimethylamine & formaldehyde and Formaldehyde may result in cross -linking of fish tissues
• Use of anti-oxidant agent before freezing

  + protein stabilizers e.g. sorbitol, sugar help increase protein hydration, less protein is produced
• Fruits & vegetables need pretreatment like blanching to reduce m.o., inactivate enzymes and block reaction that may cause damage (flavour changes)
• Fruits & vegetables; The use of calcium salts can increase the durability of cell texture (ionic interaction of calcium and pectic substances)
• Undesirable flavor formatio caused by the enzymes peroxidase & lipoxygenase
• Equipments method; Freezing using air, Plate freezing, Liquid freezing,
• Factors affect the quality of frozen food; Freezing rate, Frozen storage period, Frozen storage temperature, Storage temperature stability, Packaging
• IQF (Individually Quick Freezing)