Behaviour of Escherichia coli strains during semi-hard and hard raw milk cheese production

Abstract

The behaviour of two Escherichia coli strains, one with a high and the other with a low thermotolerance phenotype, was investigated during production and ripening of Swiss semi-hard and hard raw milk cheese. In semi-hard cheese, counts of E. coli increased during production, before a log-linear decrease occurred during ripening, with a faster rate of reduction in core than in rind samples, and faster reduction of the more heat-sensitive strain in rind samples. Nevertheless, at the end of semi-hard cheese ripening, E. coli were present at least at 1.3 log10 cfu g−1 in rind samples and remained detectable by enrichment of core samples. During the first day of hard cheese production, both E. coli strains were almost completely inactivated. Detection by enrichment was possible in one of twelve spiked cheeses after 16 weeks, indicating the potential of a thermotolerant E. coli strain to survive until the end of ripening.