Freezing Technology

5.1.1.7 Freeze Denaturation-II

Fat changes:

Fatty fish may become unpleasantly altered during cold storage but they can be protected to some extent either by glazing or by packaging in plastic bags sealed under vacuum. These oxidation changes take place more rapidly at higher temperatures and storage at a low temperature is an effective means of slowing the rate of spoilage by this method.

Color changes:

The quality of fish is often judged by appearance, and color changes which are not otherwise significant can result in fish being downgraded. The changes in the fish flesh which bring about these color changes are also retarded at lower temperatures.

Dehydration changes:

Dehydration of the product is probably the major concern of the cold store operation and the rate of drying can be linked with a number of factors in cold store design and operation.

When fish get badly dehydrated in cold storage, the surface becomes dry, opaque and spongy. As time progresses, these conditions penetrate deeper into the fish until it becomes a fibrous, very light material. Visible effects of severe dehydration on the surface of the fish are known by the term “freezer burn”. This is an unfortunate choice of term since the effect is unlikely to result from freezing in a properly designed freezer, and appears only after periods of storage in a cold store.

Frozen fish may dry slowly in cold storage even under good operating conditions. This is un desirable for reasons other than the obvious one that the product will lose weight. Drying also accelerates denaturation of the protein and oxidation of the fat in the fish. Even totally impervious wrappers used to protect the product do not give full protection if the cold store operating conditions are favorable for desiccation within the pack. In-pack desiccation prevails when there is some free space within the wrapper and temperature of the store fluctuates.

Weight loss during freezing will depend on: Type of freezer, freezing time, Type of product, Air velocity and Freezer operating conditions.

Cold Store Weight Loss Depends on Temperature, Temperature fluctuation, Humidity, Heat transfer, Air flow over the product, Radiation effects of lighting, The product, Shape and size of the product and Type of wrapper.