FREEZING AND COLD STORAGE 293 



Stansby''^ reported that oxidative changes in frozen fish were greatly re- 

 tarded by lowering the temperature and that fish held at 0°F were oxidized 

 at only about half the rate of those held at 20°F. In his review, Heen^^ 

 reports there was no detectable change in the quality of fish stored at 

 — 256°F for 6 months. However, a noticeable decrease did result in the 

 quality of fish stored for 6 months at temperatures as low as — 103°F. 



In the final analysis, the choice of product storage temperature is 

 arrived at after weighing cost of storage, maximum storage period de- 

 sired, and susceptibility of the species selected to quality changes in the 

 frozen state. Lean fish such as haddock or cod should be kept at tempera- 

 tures of 0°F or lower. Fatty fish such as mackerel, sea herring, or tuna 

 should be stored at temperatures not higher than — 20°F. 



Packaging and Glazing. Frozen fishery products undergo adverse 

 changes in quality if subjected to contact with air or loss of moisture. 

 The air surrounding the frozen product is usually of lower moisture-vapor 

 pressure than the product and acts as a sponge in removing moisture from 

 the food. This loss of moisture results in dehydration of the fish flesh to 

 a point where chalky and fibrous texture develop, discoloration takes 

 place, and off-odors and flavors develop. Contact of air with frozen fish 

 causes oxidation of the fats and results in ' 'rusting," or discoloration of 

 the flesh and development of rancid or off-odors and flavors. 



The storage life of frozen fishery products can be increased significantly 

 by using a protective shield to cover the product and thereby prevent 

 dehydration and oxidation. This protection can be obtained by packaging, 

 glazing, or a combination of these methods. 



Packaging. The packaging of frozen fishery products has been reviewed 

 by Peters" and Pottinger, et aP^. 



The packages used for frozen fishery products must have a low mois- 

 ture-vapor permeability, a low oxygen transmission rate, and be resistant 

 to absorption of oils and also water. They must also fit the product tightly 

 to minimize air spaces or voids. Products in a loosely fitting package will 

 undergo rapid loss of quality because of: (1) oxidation, from the excessive 

 air surrounding the food, and (2) dehydration, caused by a constant 

 migration of moisture from the product to the inside surface of the 

 package. 



It is generally agreed that fatty fish lose quality more rapidly than do 

 lean fish, and they therefore must receive added protection against the 

 detrimental effects of oxidation and rancidity. Conventional waxed car- 

 tons, overwrapped with films containing polyethylene, waxed paper, cello- 

 phane, or combinations of these materials, are generally not suitable for 

 packaging these fish. They are not resistant to gas transmission and do 

 not fit the product tightly. 



