Concentrates of fish protein from bycatch species produced by various drying processes

Nine fish species, Gillichthys seta, Oligoplites saurus, Eucinostomus entomelas, Synodus scituliceps, Diplectrum pacificum, Pseudopeneus grandisquamis, Xenistius californiensis, Arius seemanni, and Orthopristis reddinig, caught as bycatch by shrimp commercial fleet of the Guaymas, Sonora, México, were processed to produce protein concentrates using three drying processes (freeze-drying and heating at 65 and 110 °C). The soluble protein content from each process and species was evaluated. Significant differences were observed among processes. The composition of protein, observed by electrophoresis, was affected by temperature. Raw and freeze-dried protein from S. scituliceps showed high proteolytic activity and unwent auto-hydrolysis. The highest proteolytic activity was at 65 °C and its optimum pH was 7.5. When assayed in the presence of several protease inhibitors, the enzymes were completely inactivated by soybean trypsin inhibitor. The in vitro digestibilities of the protein concentrates were higher when obtained by low-temperature methods.