ABSTRACT
Generally, the loss of quality in fish is caused by autolytic degradation followed by microbial spoilage, both of which are functions of storage temperature of fish. Since the deteriorative changes can be minimized at reduced temperatures, the purpose of freezing is to lower the temperature to the extent that slows down spoilage as well as a result in a product which when thawed is virtually indistinguishable from its fresh counterpart. Every fish species has its own spoilage rate, and calculation of relative spoilage rate allows a fish technologist to determine the equivalent length of time of storage at 0°C. The process of freezing results in numerous structural and biochemical changes in the fish (partial dehydration of proteins, the interaction of lipids, the action of enzymes etc.), which is largely dependent on the type of freezing systems employed such as: air blast, plate, immersion, spray, CO2 and liquid nitrogen freezing. This chapter discusses the prediction of freezing times by numerical methods as suggested by various investigators along with solved numerical examples. The chapter concludes with the application of freezing systems in practice including onshore processing, freezing on board as well as changes reported in the quality of frozen fish and advanced measures to reduce the adverse effects of freezing to a minimum.
