Fate of salmonellae in calcium-supplemented orange juice at refrigeration temperature

Abstract

Recent outbreaks of salmonellosis associated with orange juice have raised interest concerning the survival and growth of Salmonella in juice supplemented with calcium. A study was done to determine the influence of various calcium supplements on the survival of salmonellae in orange juice held at 4°C for up to 32 days. Isolates of Salmonella Muenchen (inoculum 1), Salmonella isolates from humans and animals (inoculum 2), and Salmonella isolates from produce outbreaks (inoculum 3) were inoculated into pasteurized orange juices with pH values ranging from 3.96 to 4.19 and containing 350 mg of calcium per 240-ml serving (1.46 mg of calcium/ml). Populations of Salmonella declined rapidly in juice containing calcium lactate (CaL), with counts decreasing from 4.86 log10 CFU/ml to <1 log10 CFU/ml within 16 days, regardless of the Salmonella serotypes present in inoculum. Counts decreased from 4.89 log10 CFU/ml to <1 log10 CFU/ml in orange juice supplemented with CaL and tricalcium phosphate (TCP) within 30 days. These reductions were significantly (P ≤ 0.05) higher than those of the control (no calcium added), in which Salmonella populations decreased 3.19 ± 0.20 log10 CFU/ml over 32 days. Populations in orange juice containing TCP or calcium citrate (CC) declined 1.34 ± 0.20 log10 CFU/ml and 1.96 ± 0.20 log10 CFU/ml, respectively, over 32 days. These counts were significantly higher than respective control counts in juice stored for 32 days. Populations of Salmonella of inoculum 3 inoculated into juice containing calcium citrate malate (CCM) were significantly higher than in the control. Higher numbers of cells in inoculum 3 also survived compared to numbers of cells of inocula 1 or 2 in juice supplemented with CCM. This study reveals that the form of calcium used to supplement orange juice influences the ability of salmonellae to survive.