Comparative survival of Salmonella typhimurium DT 104, Listeria monocytogenes, and Escherichia coli O157:H7 in preservative-free apple cider and simulated gastric fluid

This study compared the survival of three-strain mixtures (ca. 107 CFU ml−1 each) of Salmonella typhimurium DT104, Listeria monocytogenes, and Escherichia coli O157:H7 in pasteurized and unpasteurized preservative-free apple cider (pH 3.3–3.5) during storage at 4 and 10°C for up to 21 days. S. typhimurium DT104 populations decreased by <4.5 log10 CFU ml−1 during 14 days storage at 4 and 10°C in pasteurized cider, and by ≥5.5 log10 CFU ml−1 during 14 days in unpasteurized cider stored at these temperatures. However, after 7 days at 4°C, the S. typhimurium DT104 populations had decreased by only about 2.5 log10 CFU ml−1 in both pasteurized and unpasteurized cider. Listeria monocytogenes populations decreased below the plating detection limit (10 CFU ml−1) within 2 days under all conditions tested. Survival of E. coli O157:H7 was similar to that of S. typhimurium DT104 in pasteurized cider at both 4 and 10°C over the 21-days storage period, but E. coli O157:H7 survived better (ca. 5.0 log10 CFU ml−1 decrease) than S. typhimurium DT104 (>7.0 log10 CFU ml−1 decrease) after 14 days at 4°C in unpasteurized cider. In related experiments, when incubated in simulated gastric fluid (pH 1.5) at 37°C, S. typhimurium DT104 and L. monocytogenes were eliminated (5.5–6.0 log10 CFU ml−1 decrease) within 5 and 30 min, respectively, whereas E. coli O157:H7 concentrations decreased only 1.60–2.80 log10 CFU ml−1 within 2 h.