Detection of extracellular bound proteinase in EPS-producing lactic acid bacteria cultures on skim milk agar

Aims: Skim milk agar was developed to investigate extracellular cell-bound proteinase in yogurt cultures, Streptococcus thermophilus and Lactobacillus bulgaricus. Methods and Results: The Lact. bulgaricus cultures produced more extracellu lar cell-bound proteinase than did Strep. thermophilus cultures. Strong pos itive correlations between the size of the exopolysaccharide (EPS) layer an d extracellular cell-bound proteinase were found for both Streptococcus and Lactobacillus cultures. Conclusions: Strong positive linear relationships existed between the EPS s ize and colony size and the diameter of clear zone and colony size for Stre ptococcus cultures, whereas weak positive linear relationships were observe d for Lactobacillus cultures. Significance and Impact of the Study: These data are useful to validate the relationship between extracellular proteinase and the EPS size of LAB. Als o, a convenient medium to detect the presence of extracelluar cell-bound pr oteinase of LAB is valuable for dairy industries.