PROTEIN EXTRACTS AND AGGREGATES FORMING IN MINCED COD (GADUS-MORHUA) DURING FROZEN STORAGE

Natural actomyosin was extracted from frozen minced cod muscle stored for up to 62 weeks at -20 degrees C with 0.6 M NaCl, and the insoluble aggregates, when formed, were solubilized successively with 2% sodium dodecyl sulfate (SDS) and 2% SDS + 5% beta-mercaptoethanol (ME) solut ions, giving extracted fractions S1 (NaCl), S2 (SDS), and S3 (ME + SDS ), precipitates insoluble in 0.6 M NaCl (P1) and 2% SDS (P2), and a pr ecipitate not soluble in any of the agents used (P3). SDS polyacrylami de gel electrophoresis (SDS-PAGE) of fraction S1 showed that the propo rtion of the major proteins changed during frozen storage. Size exclus ion chromatography showed a decrease in the peak containing myosin hea vy chain (MHC) and actin (Ac). Transmission electron microscopy (TEM) of S1 showed at the outset a filamentous morphology associated with gl obules interconnected crosswise. As storage progressed, the number and size of aggregates increased. In fractions S2 and S3, the major prote ins detected by SDS-PAGE were MHC and Ac. TEM showed a greater abundan ce of ring-shaped structures than in S1. TEM of the insoluble fraction s showed a sarcomere-like structure, more pronounced the milder the so lubilizing treatment and the longer the storage time.