The effect of proteolytic activity of starter cultures on technologically important properties of yogurt.

In this study, the effects of proteolytic activity of yogurt starter bacteria on physicochemical and technological properties of yogurt were investigated. Moreover, impact of proteolytic activity and production of exopolysaccharide (EPS) on the performance of each strain were screened. In order to compare the textural properties of yogurt samples, four parameters were evaluated: syneresis, water-holding capacity, cohesiveness, and hardness. Results showed that strains with high proteolytic activity had lower acidifying activity during fermentation and storage. Samples containing EPS-producing starter cultures had low proteolytic activity except samples K, L, and M. These differences related to nature and characteristics of each strain. Counts of starter cultures in samples produced using strains with high proteolytic activity were higher than other samples. Textural analysis data showed significant differences ( < .05) among strains in the four tested parameters. Strains with high proteolytic activity showed lower texture properties than other samples. Evaluation of sensory characteristics also showed samples prepared using strains with low or medium proteolytic activity and produced with EPS-producing strains have higher overall acceptability than other samples. Accordingly, microbial, physicochemical, and sensory properties of produced yogurts confirm that proteolytic activity is one of the most effective factors in quality of product and performance of each strain.