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. 10(7) CFU ml (-1) each) of Salmonella typhimurium DT104, Listeria monocytogenes, and Esc herichia coli O157:H7 in pasteurized and unpasteurized preservative-free ap ple cider (pH 3.3-3.5) during storage at 4 and 10 degrees C for up to 21 da ys. S. typhimurium DT104 populations decreased by <4.5 log(10) CFU ml(-1) d uring 14 days storage at 4 and 10 degrees C in pasteurized cider, and by gr eater than or equal to 5.5 log(10) CFU ml(-1) during 14 days in unpasteuriz ed cider stored at these temperatures. However, after 7 days at 4 degrees C , the S. typhimurium DT104 populations had decreased by only about 2.5 log( 10) CRT ml(-1) in both pasteurized and unpasteurized cider. Listeria monocy togenes 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 degrees C over the 21-days storage period, but E. coli O157:H7 surv ived better (ca. 5.0 log(10) CFU ml(-1) decrease) than S. typhimurium DT104 (>7.0 log(10) CFU ml(-1) decrease) after 14 days at 4 degrees C in unpaste urized cider. In related experiments, when incubated in simulated gastric f luid (pH 1.5) at 37 degrees C, S. typhimurium DT104 and L. monocytogenes we re eliminated (5.5-6.0 log(10) CFU ml(-1) decrease) within 5 and 30 min, re spectively, whereas E. coli O157:H7 concentrations decreased only 1.60-2.80 log(10) CFU ml(-1) within 2 h. (C) 1999 Elsevier Science B.V. All rights r eserved.