Behavior of Salmonellae During Manufacture and Ripening of Manchego Cheese

Abstract

Six Salmonella strains were inoculated into 12 vats (2 vats/strain) of pasteurized sheep milk at a level of 104 cells/ml, and Manchego cheese was manufactured by usual procedures, with 1% of a Streptococcus lactis culture as starter. Growth of Salmonella occurred during the first 6–9 h, with mean increases in log counts of 1.67, 1.49 and 1.71 respectively for Salmonella enteritidis, S. typhi and S. typhimurium; data inversely correlated to pH decrease. Mean numbers of Salmonella declined during the first week by 4.43, 1.18 and 3.97 log cycles for the three serotypes, respectively, with a significant correlation between decreases in pH and in Salmonella log counts. Salmonella survived for 4 weeks in 9 vats, for 6 weeks in 3 vats and was absent from all lots of 8-week Manchego cheese. Brilliant green agar yielded the highest productivity among five selective agars used for the enumeration of Salmonella by direct-plating procedures, while enrichment in selenite cystine broth followed by streaking to bismuth sulfite agar gave the highest Salmonella recovery of all eight broth-agar combinations tested.