Intrinsic Product Quality

Following Jul's work (5) that drew attention to the PPP factors, numerous researchers have confirmed and extended the understanding of the importance of initial product quality, principally in terms of freshness of the living tissue or formulated food. Perhaps the most dramatic claim showed that the PSL of squid held for only 24 h in ice between death and freezing was reduced by one-half compared with a similar squid frozen immediately on death (14). Cyroprotectants have an important part to play in modifying products to increase their PSL. Cryoprotec-

tants commonly employed include sugars, amino acids, polyols, and so on. Indeed, the loss of PSL in the frozen state consequent upon loss of "freshness" in the raw material may be considered to be due to a loss of naturally occurring cryoprotectants. Antifreeze proteins have been found to depress the freezing point markedly (Antarctic fish can survive without freezing at — 70°C), and the possibility that the use of antifreeze proteins may be able to improve the quality of frozen foods is being actively researched (15).

Processing

Any enzyme-mediated reactions will be greatly accelerated by freezing. The cryconcentration effect, caused by the removal of water in the form of ice from the medium, may be 5 or 10 times and is only feebly compensated for by the lowering of temperature. A cooked product, in which the enzymes have been destroyed, is more stable. This enhanced enzymic activity on freezing (which results in loss of color, flavor, and development of off-flavors in cold storage) calls for inactivating the enzymes in vegetables (such as sweet corn, peas, and green beans) by blanching; the choice of which indicator enzyme ensures adequate blanching is addressed by Whitaker (16).

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