Muscle Protein Composition of Sardine and Mackerel

Abstract

Protein composition of the dark and the white muscle from the sardine, Sardinops melanosticta, was determined. Through the pre-, in-, and post-rigor stages, each muscle showed a fairly consistent protein composition: in the dark muscle, 23-29% sarcoplasmic, 62-66% myofibrillar, 6-9% alkali-soluble, and 2-3% stroma fraction. In the white muscle, in the above order, 33-37%, 54-61%, 1-5%, and 1-2%, respectively. The content of connectin, one of the stroma proteins, was higher in the dark than in the white muscle. After the dark muscle was kept frozen at-80°C for two weeks, the percentage of sarcoplasmic fraction increased to 37%, while that of myofibrillar fraction decreased down to 56%. No corresponding alteration occurred with the white muscle during frozen storage.
By ultracentrifugal analysis, no actomyosin peak was observed in the myofibrillar fraction of the dark muscle. With the fraction from the white muscle, an actomyosin peak appeared, the sedimentation coefficient of which was 16.0 S at the pre-rigor stage and increased to 22.5 S at the post-rigor stage.
Similar results were obtained with the mackerel, Pneumatophorus japonicus japonicus.