Abstract: Casein degradation in the presence of two Lactobacillus helveticus strains (strain 6 and strain 9) was investigated based on the formation of transparent zone from hydrolyzed protein, the degree of hydrolysis and the concentration of peptides produced. Strain 9 enzyme has a significant higher activity to degrade casein than that of strain 6. The degree of casein hydrolysis by strain 9 grows gradually as fermentation time delaying from 0 h to 48 h, reaches to 17.3%. The concentration of peptides from casein derived by strain 9 cells is 0.62 mg/ml following 48 h incubation at 37 ℃ SDS-PAGE analysis and profiles of Sephadex G-25 gel filtration also proved that L. helveticus stain 9 is able to release more peptides from casein as co-culture time delaying. The present study indicated that utilization of L. helveticus strain 9 with high proteolytic activity can provide a promising technology to produce potential bio-activity peptides from casein.

Key words: casein, Lactobacillus helveticus 9, proteolytic activity, degree of hydrolysis