Fates of Salmonella Enteritidis and Cronobacter sakazakii in various multiple‐strain yogurts and kefir during cold storage

Abstract

AbstractMany multiple‐strain fermented milks such as yogurt and kefir have been developed and consumed to improve their nutritional and functional benefits. Since these fermented milks can be a vehicle of foodborne illness, we investigated the fates of Salmonella Enteritidis and Cronobacter sakazakii in four fermented milks: multiple‐lactic acid bacteria (multi‐LAB) yogurt, multiple‐LAB‐Bifidobacterium (multi‐LAB‐BIF) yogurt, pH 4.5 kefir (mild kefir), and pH 3.6 kefir (strong kefir). Each was inoculated with 5.6 and 5.8 log cfu/ml of S. Enteritidis and C. sakazakii, respectively, and stored at 4°C for 5 days. Strong and mild kefirs exhibited more potent antimicrobial activities than multi‐LAB and multi‐LAB‐BIF yogurts, inactivating all viable pathogenic bacteria within 1 and 5 days, respectively. Despite having lower pH values than mild kefir (pH 4.49), multi‐LAB (pH 4.25) and multi‐LAB‐BIF (pH 4.38) yogurts failed to clear viable S. Enteritidis cells in 5 days (> 5 log cfu/ml cells survived).Practical applicationsYogurt is one of the most popular fermented milk, and has been implicated in several human foodborne outbreaks. Kefir is unique fermented milk containing multiple strains of lactic acid bacteria and yeast. In this study, we investigated the fates of Salmonella Enteritidis and Cronobacter sakazakii in these fermented milks. Two types of commercial yogurt failed to clear viable S. Enteritidis cells in 5 days, whereas kefir successfully killed all viable S. Enteritidis and C. sakazakii cells in 5 and 4 days, respectively, even with significantly higher pH values suggesting that pH might not be a suitable indicator to ensure the microbiological safety of yogurts and kefir, and that pathogens face other antimicrobial hurdles than low pH and high acidity. Considering the potent self‐clearance effects of kefir against foodborne pathogens, novel yogurt products containing strains with potent antimicrobial activity such as kefir microorganisms could be newly developed in the future.