Analysis of the Protein Constituents of Drip From Thawed Fish Muscle

Abstract

Fishery products preserved by freezing potentially have characteristics more like those of fresh fish than do products preserved by any other process currently in use. Despite the widespread acceptance of frozen fishery products, however, a decided consumer preference for fresh fish often exists. The reasons for this preference may be attributed to a progressive deterioration in quality of the frozen product, particularly after prolonged cold storage. When fish muscle is frozen and subsequently thawed, a cloudy, liquid phase called drip exudes from the muscle. In addition, when the thawed muscle is cooked, the surface of the cooked flesh often is coated with an unsightly white deposit of coagulated drip proteins, commonly referred to as curd. Further, the thawed fish when cooked often toughens and becomes fibrous as compared with cooked fish that has never been frozen. The rate of quality deterioration in frozen fish is related not only to cold storage conditions but also to species differences.Several different theories have been proposed concerning the origin of drip in frozen fish,muscle and reviews dealing with this problem and factors influencing the production of drip have been discussed elsewhere (3, 7). The most recent evidence (7,14,17). however, would suggest that drip is due to denaturation of proteins which normally tend to hold the water of the muscle and to changes in the cellular structure of the muscle brought about by the formation of ice. The general effect of freezing and the rate of freezing on the fine structure of fish muscle has been demonstrated by histological techniques, although experimental findings often appear rather contradictory.Love (10) recently has suggested that the appearance of desoxypentosenucleic acid (DNA) in the expressible fluid from thawed muscle indicates rupture of the cell membrane, with liberation of nuclear material.The fact that disintegrated fresh tissue does not liberate an appreciable quantity of muscle juice, however, would suggest that the mere rupture of the cell membrane in itself does not fully explain the release of large quantities of drip when the same material is frozen and thawed. It has been demonstrated (14) that the retention of cellular fluids or drip is related to the power of muscle proteins to imbibe free liquid. This imbibing power is influenced by electrolyte content and by pH and a zone of minimum effect is exhibited in the regions of the isoelectric points of the fish muscle proteins (27). The aggregation or loss of solubility of actomyosin-the principal contractile protein of the myofibril-by freezing, and its subsequent inability to rehydrate has been demonstrated by many workers ( 6 ) . Dyer (6) reports that the sarcoplasmic or non-contractile proteins, however, show no change of solubility on freezing except after very long storage. The denaturation of the contractile proteins was also suggested by Mahadevan and Carter (12), who detected a permanent and constant decrease in volume of fish flesh after freezing and thawing. Salt dehydrati...

Deterioration of Fresh‐Water Whitefish Muscle During Frozen Storage at −10°C

“…Seagran ( 1958)) using paper electrophoresis, found by comparison of electrophoretograms that no qualitative differences were apparent for unfrozen and frozen (2 months at -20°C) yellow-striped rock fish muscle. Recently, disc electrophoresis has been used to identify fish species by examining the water-soluble protein patterns (Mancuso, 1964).…”

Effect of storage temperatures on the formation of disulfides and denaturation of milkfish myosin (Chanos chanos)

“…Jiang (1977) and Jiang et al (1985) found that mullet and amberfish muscle proteins were much more stable when stored at -40 °C than at -20 °C. Although no changes in extractability, sedimentation constant, and intrinsic viscosity of AM were found with fish muscle frozen by liquid nitrogen (Dyer, 1951;Segran, 1956;Suzuki et al, ,1965Noguchi and Matsumoto, 1970), protein denaturation occurred and further progressed during storage at -8 to -10 °C (Suzuki et al, 1965).…”

Effect of storage temperatures on the formation of disulfides and denaturation of Tilapia hybrid actomyosin (Tilapia nilotica .times. Tilapia aurea)

“…Jiang (1977) and Jiang et al (1985) reported that mullet and amberfish muscle proteins were much more stable when stored at -40 °C than at -20 °C. No significant changes in extractability, sedimentation constant, and intrinsic viscosity of AM were found in fish muscle frozen by liquid nitrogen (Dyer, 1951;Segran, 1956;Suzuki et al, ,1965Noguchi and Matsumoto, 1970). However, protein denaturation occurred during frozen storage when the storage temperature was not low enough (Suzuki et al, 1965).…”