Isolation, screening and characterization of thermophilicBacillusspecies isolated from dairy products

摘要

Proteolytic thermophilic bacterial cultures (171 strains) were isolated from different milk and milk products. After screening these isolates for protease production in a liquid medium, fifty that exhibited enzyme activity in excess of 100 units/ml were selected and identified. Twenty‐nine wereBacillus stearothermophilus(constituting 58 of the total), twelve wereB. coagulans, five wereB. circulansand four wereB. licheniformis. Skim milk powder contributed the maximum number ofB. stearothermophilus(64.7) followed by raw milk (63.2) and pasteurized milk (44.4). When the culture supernatant liquids from the selected isolates were given heat treatment, five cultures retained 100 protease activity at 65°C for 30 min. Protease ofB. stearothermophilusRM‐67 had the maximum heat resistance because it retained 87.5 of its activity at 70°C for 3