Identification of halophilic strains and its proteolytic degradation of fish protein

Aims: The research was carried out to study the isolation, identification of protease-producing halophilic strains and investigation of hydrolysis of various anchovy muscle proteins by a halophilic protease from strain SR5-3. Methodology and results: Seven protease-producing halophilic strains were isolated from Thai fermented food. On the basis of phenotypic and chemotaxonomic characteristics including high DNA-DNA relatedness (70.0-77.3%), six strains were identified as Virgibacillus halodenitrificans and a halophilic bacterium, the highest protease producer, SR5- 3, was named as Halobacillus. The hydrolysis of different fish proteins by a halophilic protease from strain SR5-3 was determined. The halophilic protease completely digested fish collagen and myosin heavy chain (MHC), but partially hydrolysed actin. In order to study the effect of NaCl on proteolytic activity, the degree of hydrolysis of purified protease and commercial proteases towards anchovy protein powder was compared. The halophilic protease showed a greater degree of hydrolysis towards anchovy substrate than that from commercial proteases in the presence of 25% NaCl. Conclusion, significance and impact study: This study revealed that six V. halodenitrificans strains and a Halobacillus strain SR5-3 secreted halophilic proteases. Upon digestion of fish protein, a halophilic protease showed higher protease activity and stability in heavily NaCl concentration, suggesting its potential application in acceleration of fish sauce production.