Survival of Salmonella Tennessee, Salmonella Typhimurium DT104, and Enterococcus faecium in peanut paste formulations at two different levels of water activity and fat

Abstract

Long-term survival of heat-stressed Salmonella Tennessee, Salmonella Typhimurium DT104, and Enterococcus faecium was evaluated in four model peanut paste formulations with a combination of two water activity (a w) levels (0.3 and 0.6) and two fat levels (47 and 56%) over 12 months at 20 ± 1°C. Prior to storage, the inoculated peanut paste formulations were heat treated at 75°C for up to 50 min to obtain an approximately 1.0-log reduction of each organism. The cell population of each organism in each formulation was monitored with tryptic soy agar plate counts, immediately after heat treatment, at 2 weeks for the first month, and then monthly for up to 1 year. The log reductions (log CFU per gram) following 12 months of storage were between 1.3 and 2.4 for Salmonella Tennessee, 1.8 and 2.8 for Salmonella Typhimurium, and 1.1 and 2.1 for E. faecium in four types of model peanut paste formulations. Enhanced survivability was observed in pastes with lower a w for all organisms, compared with those with higher a w (P 〈 0.05). In contrast, the effect of fat level (47 and 56%) on survival of all organisms was not statistically significant (P 〉 0.05). Whereas survivability of Salmonella Tennessee and Typhimurium DT104 did not differ significantly (P 〉 0.05), E. faecium demonstrated higher survivability than Salmonella (P 〈 0.05). Salmonella survived in the model peanut pastes well over 12 months, which is longer than the expected shelf life for peanut butter products. The information from this study can be used to design safer food processing and food safety plans for peanut butter processing. Copyright ©, International Association for Food Protection.