Isolation, screening and characterization of thermophilic Bacillus species isolated from dairy products

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Abstract
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, 50 that exhibited enzyme activity in excess of 100 U/ml were selected and identified. Twenty-nine were B. stearothermophilus (constituting 58% of the total), 12 were B. coagulans, 5 were B. circulans and 4 were B. licheniformis. Skim milk powder contributed the maximum number of B. 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, 5 cultures retained 100% protease activity at 65.degree. C for 30 min. Protease of B. stearothermophilus RM-67 had the maximum heat resistance, because it retained 87.5% of its activity at 70.degree. C for 30 min.

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