The influence of proteases on the browning of dried squid products processed by air-drying.

To clarify why mantle meat from Japanese common squid (Todarodes pacificus) dried products discolor dramatically when processed by air-drying, the role of endogenous protease(s) on browning during the processing of dried squid products was studied. The involvement of endogenous protease(s) in the generation of Free Amino Acids (FAAs) participating in the Maillard reaction was characterized. The browning and myosin heavy chain degradation during air-drying were obviously mitigated by the addition of metalloprotease inhibitors, especially EGTA and 1,10-phenanthroline, followed by serine proteinase inhibitor, especially PMSF. The amount of total FAAs in dried products increased by only 0.17% with the addition of 1,10-phenanthroline and 5.0% with added EGTA. In autolysis models, protein autolysis was almost completely inhibited by 1,10-phenanthroline. The addition of, 1,10-phenanthroline inhibited the increase in total FAAs including arginine (Arg), followed by EGTA and PMSF. The results indicated that endogenous metalloproteases and serine proteases might influence the generation of FAAs including Arg, and contribute to product discoloration during air-drying.