Identification of proteolytic activities of gel-degrading factors in three lizardfish species [Saurida undosquamis, S. wanieso, S. elongata]

The inhibitory effects of several selected proteinase inhibitors, soybean trypsin inhibitor, leupeptin, antipain, E-64, NEM and EDTA, on myosin heavy chain (MHC) degradation of unwashed and washed meat gels from three lizardfish species, maeso or true lizardfish Saurida undosquamis, wanieso Saurida wanieso, tokageeso or shortfin lizardfish Saurida elongata, were investigated in order to identify the proteolytic activities of gel-degrading factors (GDFs) existing in mat. It was apparent that the proteolytic activities of GDFs responsible for MHC degradation of meat gels from all species at 40°C resulted from two myofibril-associated (Mf) type proteinases, mainly of serine proteinase and slightly of cysteine proteinase. In addition, as indicated by the amino acid patterns obtained from TCA-soluble fraction of meat gels with the presence of various inhibitors, these proposed proteinases were not distinct in these three species. With regard to the MHC degradation at 60°C, the proteolytic activity present in GDFs of maeso, proposed as myofibril-associated gel degrading factors (Mf-GDFs), belonged to cysteine proteinase while that of wanieso and tokageeso were sarcoplasmic-type serine proteinases. The Mf-GDF corresponding to the MHC degradation at 60°C, which occasionally occurs in wanieso meat gel, showed the proteolytic activities of serine proteinase.