Survival of Salmonella enteritidis phage type 30 on inoculated almonds stored at -20, 4, 23, and 35°C

Abstract

To evaluate the survival of Salmonella on raw almond surfaces, whole almond kernels were inoculated with Salmonella Enteritidis phage type (PT) 30 collected from a 24-h broth culture or by scraping cells from an agar lawn. Kernels inoculated with lawn-collected cells to 8, 5, 3, and 1 log CFU per almond alter a 24-h drying period were stored for 161 days at 23 ± 3°C. Calculated rates of reduction were similar for the four inoculum levels (0.22, 0.28, 0.29, and 0.22 log CFU/month, respectively). Kernels inoculated to 7.1 or 8.0 log CFU per almond after drying were stored for 171 or 550 days, respectively, at selected temperatures, including -20 ± 2°C, 4 ± 2°C, 23 ± 3°C, and 35 ± 2°C. No significant reductions of Salmonella were observed during storage at -20 and 4°C over 550 days. At 35°C, a biphasic survival curve was observed, with calculated reductions of 1.1 log CFU/month from days 0 to 59 and no significant reduction from days 59 to 171. At 23°C, reductions of 0.18 and 0.30 log CFU/month were calculated for 171 and 550 days of storage, respectively. When combined with data from the study of inoculum levels, an overall average calculated reduction at 23°C was 0.25 ± 0.05 log CFU/month. Significantly greater reductions were observed during the 24-h drying period when broth-collected cells were used as the inoculum, suggesting that cells collected from agar lawns were more resistant to drying. However, after initial drying, the rates of reduction at 23°C did not differ significantly between the inoculum preparation methods. Salmonella Enteritidis PT 30 survives for long periods on almond kernels under a variety of common storage conditions. Copyright ©, International Association for Food Protection.