Isolation and characterization of halophilic alkaliphilic bacteria producing protease and their use to accelerate fish sauce fermentation
Abstract
Halophilic and alkaliphilic bacteria producing protease have potential applications in food industry such as acceleration of fish sauce fermentation. In this study, 449 alkaliphilic strains were isolated from 56 samples collected from coast line, of which 190 strains produced protease. Three strains 2.2, 2.20 and 18.2 exhibit high protease activity, especially strain 2.2 showed highest protease activity and optimally grew in 3-4% NaCl medium. Protease produced by strain 2.2 optimally activated at pH 8, 45oC and 3% NaCl. These properties are useful for accelerating the fermention process during fish sauce production. Three strains 2.2, 2.20, 18.2 were used to examine their ability to hydrolyze fish. The result showed that after 15 days of hydrolysis, the total nitrogen concentration in fish fluid added with these strains was higher than control samples, especially samples added with strain 2.2 gave a nitrogen content nearly twice as much as controls. Moreover, the fish fluid of samples added starter cultures from these strains was also shown to be more clear and less stinking than controls in sensory research.