Sarcoplasmic reticulum Ca2+-ATPase and cytochrome oxidase as indicators of frozen storage in cod (Gadus morhua)

Activities of 2 membrane-bound enzymes, Ca2+-ATPase from the sarcoplasmic reticulum and cytochrome oxidase from the inner mitochondria membrane, were measured during frozen storage of cod. Enzyme activities were higher in cod muscle samples frozen at -30 degreesC than at -20 degreesC. Freezing-induced activation of both enzymes was observed and the activation was amplified by ice storage prior to freezing. Sensory evaluation conducted at 9 mo of frozen storage showed differences between the sensory properties of cod frozen immediately after catch and frozen after 3 d of storage on ice. These results indicated that the enzymes might be useful as indicators of quality changes by frozen storage.