Influence of freezing on quality of foods

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Influence of freezing on quality of foods
« on: November 10, 2013, 11:00:37 AM »
Food products thawed after cold storage should ideally be indistinguishable from the fresh product (this obviously does not apply to products such as ice cream that are consumed in the frozen state).The formation of ice crystals during freezing can downgrade the quality of the food by one of the following three mechanisms:

(a) Mechanical damage to the food structure. The specific volume of ice is greater than that of water (greater by about 10%) and therefore the expanding ice crystals compress the food matrix. Ice crystal expansion in some fruits such as strawberry damages them severely, because of their delicate structure (the fruit becomes ‘soggy’ on thawing). On a macroscopic scale, during rapid cryogenic freezing, thermal stresses due to expansion may crack the food.

(b) Cross-linking of proteins (in fish and meat). Decrease in the amount of liquid water available to the proteins and increase of electrolyte concentration during freezing lead to aggregation and denaturation of actomyosin .

(c) Limited re-absorption of water on thawing. This is connected with mechanism (b). Again, we can take the example of animal tissue in which the muscle proteins, during frozen storage, become ‘denuded’ of their hydration water and cross-linked. On thawing, the tissue may not re-absorb the melted ice crystals fully to the water content it had before freezing. This leads to undesirable release of exudate – ‘drip loss’ – and toughness of texture in the thawed muscle, the main attributes determining quality.

Source: Frozen Food Science and Technology – Judith A. Evans
Taslim Ur Rashid
Lecturer
Department of Nutrition and Food Engineering
Daffodil International University