Novel method for study of the extracellular cell-bound proteinase from lactic acid bacteria

摘要

Skim milk agar was developed to investigate extracellular cell-bound proteinase in yogurt cultures. The agar was inoculated with yogurt starter cultures Streptococcus thermophilus and Lactobacillus bulgaricus, incubated anaerobically at 37C for 48 h, and then stored at 4C for 3 days. Both S. thermophilus and L. bulgaricus colonies, which could produce extracellular proteinase, developed clear zones in skim milk agar. The clear zone produced by L. bulgaricus was bigger (4.551-4.620 mm) than that produced by S. thermophilus (2.350 mm). This result suggested that L. bulgaricus produced more extracellular cell-bound proteinase. The clear zone on skim milk agar can be used to easily determine the presence of extracellular cell bound proteinase, and furthermore, the size of clear zone might indicate proteolytic activity.