Liquid loss in thawed cod—Deconvoluting the effects of freezing-rate, freezing cycles, frozen storage time, and thawing-rate through a full factorial design

Abstract

Fish is a highly perishable product and freezing is the obvious way to increase shelf life. The freezing process involves the initial freezing, a frozen storage period and thawing—all of which influence the quality of the end product. In this study, the quantity of liquid loss is used as an indication of the structural damage induced by these processes. A full factorial experiment design addresses the effects of freezing and thawing rates (fast vs. slow), number of freezing cycles (1 vs. 2) and frozen storage (1 year vs. 1 week). The results show strong evidence that fast processes of freezing and thawing reduce the subsequent liquid loss. However, 1 year frozen storage at −20°C induces high liquid loss independently of the freezing and thawing rates. Adding a second freezing cycle also adds to the liquid loss upon final thawing. By increasing the number of processing steps (additional freezing cycles) the strain put upon the samples progressively increases. This leaves samples at the end of long sequences of processing especially sensitive to damage caused by ice crystals. In this way, the thawing protocol might be of high importance, especially during the last freezing cycle of twice frozen samples. Practical Application: In order to minimize liquid loss through production of frozen seafood, it is imperative that producers use the best practice at every stage. Liquid loss influences yield through production, but it also contributes to quality parameters relevant to both producers and consumers. Every stage of the production impacts liquid loss, and examining and classifying the different processing steps separately is the common approach to assess the effect. For the final product however, the impact of one isolated step is entangled in the combined effect off all the different processing steps. In this study, we have examined the processing continuum from the first freezing to the last thawing, including the effects of an extra freeze cycle and frozen storage period. In this way, we demonstrate the risk of pitfalls through such processing and also highlight the process combinations that are synonymous with low liquid loss.