AGGREGATION OF MYOFIBRILLAR PROTEINS IN HAKE, SARDINE, AND MIXED MINCES DURING FROZEN STORAGE

The effect of frozen storage on the loss of extractability of natural actomyosin (NAM) with 0.6 M NaCl (PI) was studied in hake (Merluccius merluccius), sardine (Sardina pilchardus), and mixed minces in varying proportions stored for up to 1 year at -20 degrees C. The objective w as to ascertain the types of bonds established among the proteins. The unextracted NAM was treated with different extracting agents to cleav e secondary bonds (2% SDS, 2% SDS + 8 M urea) and secondary and disulf ide bonds [2% SDS + 5% beta-mercaptoethanol (ME)]. There was more NAM extracted from the mixes with higher percentages of sardine, although this effect was weaker than might have been expected from the percenta ges of sardine in the mixes. In hake, for up to 8 months of storage, t he bulk of the proteins not extracted in 0.6 M NaCl was extracted with SDS + urea or SDS + ME, with extraction declining as storage progress ed. This suggests that the amount of protein linked by covalent bonds increased with time. In sardine and mixed lots, a high percentage of p roteins linked by covalent bonds was detected earlier, although no cle ar pattern emerged in terms of hake/sardine ratios. SDS-PAGE showed th at treatment with SDS + urea and SDS + ME extracted protein in the for m of small aggregates that were retained in the stacking gel. These ag gregates were also found in the SDS extracts from the sardine and mixe d minces.