Proteolytic organisms in butter

Abstract

Colonies producing zones on milk agar plates of routine butter samples were examined and it was found that in 55 per cent. of the zones, casein was not precipitated by tannic acid.
Organisms showing zone formation were isolated and examined for proteolytic properties. Approximately 20 per cent. of cultures showing proteolysis on milk agar were not caseolytic on casein agar, in casein broth or in milk.
Many organisms which were proteolytic were found to be heat-resistant.
In this series of cultures there was no relationship between proteolysis and lipolysis.
Only three cultures of Gram-negative rods were isolated among the proteolytic types. The remaining 47 cultures studied in detail were Gram-positive cocci and Gram-positive rods.
Statistical analysis of results for a large number of routine butter samples showed a relatively high correlation between total bacterial count and casein digester count and also between casein digester count and the presumptive coliform test.
It was concluded that there was no advantage in including a test for proteolysis on milk agar in the routine bacteriological tests for butter.