Behavior of Escherichia coli O157:H7 during the ripening of herby cheese manufactured from raw milk

Abstract

This study was conducted to determine the survival of Escherichia coli O157:H7 during the ripening period of herby cheese made traditionally from raw cow milk. The cheese milk was inoculated with E. coli O157:H7 at the level of 3 log and 5 log cfu/mL, and then both manufactured herby cheeses were divided into two groups equally. The herby cheeses were stored by using two different methods for ripening, either embedding into the soil or putting into brine, and analyzed on day 1, 7, 15, 30, 60 and 90 of ripening. At the end of the storage period, E. coli O157:H7 could not be detected in embedded herby cheese at both levels of the inocu­lation; whereas the number of the bacterium was just decreased to 2.30 and 4.48 log MPN/g in brined herby cheese for each inoculation levels respectively . Additionally, micrococci/staphylococci count, acidity and salt values in all cheese groups were higher compared than the initial level; total mesophilic bacteria, lactic acid bacteria, enterobacteriaceae count and a w value were lower than the initial level. While pH value was higher in embedded cheese than initial level, it was lower in brined cheese. In conclusion, E. coli O157:H7 could survive at least 60 days in embedded herby cheese and till the last days of the ripening in brined herby cheese. This point should be taken into account for the potential risk to public health.