Technological characterization of lactic acid bacteria protease isolated from traditional Chinese fermented milk

The proteolysis activity, texture, viscosity, particle size and sensory evaluation of 12 isolates identified by 16S rDNA sequence analysis, which were screened from 123 lactic acid bacteria (LAB) isolated from Chinese traditional fermented milk, were evaluated. Proteolytic activity of these selected strains ranged from 2.43 to 11.60mmol Leu/L of milk. Texture analysis indicated that yogurts of Streptococcus thermophilus were of higher value than those of Lactobacillus delbrueckii at all levels of measurement. Apparent viscosity of yogurt varied considerably among the strains, with values ranging from 4790 to 9870mPa·s. All the strains showed excellence in firmness, consistency, cohesiveness, viscosity and little difference in the particle size. L.delbrueckiiCH9-3 4.0, SB3 and SB25 provided excellent protease activity and could be used as yogurt culture to improve the curd quality. S.thermophilusLBH, Q10 and L.delbrueckiiSP1.1 showed high viscosity, and could be mixed with other LAB strains to obtain thick yogurts.