Characterization of proteases of Bacillus subtilis strain 38 isolated from traditionally fermented soybean in Northern Thailand

Abstract

Eighty-two bacillus strains were isolated from Thai fermented soybeans (thua nao), of which thirty-nine were identified as Bacillus subtilis. Crude proteins from these B. subtilis strains were investigated for their proteolytic activity. When tested on skim milk agar, the crude proteins of B. subtilis strain 38 exhibited the highest proteolytic activity (a clear zone with an average area of 480 mm2). Optimal pH and temperature of the proteases from B. subtilis strain 38 were found to be at 6.5 and 47 °C, respectively. The proteases were unstable and rapidly decreased in activity when heated at 60 °C. Various protease inhibitors were tried, only 1, 10-phenanthroline decreased the enzyme activity indicating the presence of metalloproteases. In addition, we attempted to produce fermented soybeans using the B. subtilis strain 38 as a starter culture.