Survival and Thermal Resistance of Salmonella Enteritidis PT 30 on Almonds after Long-Term Storage

• Published in: Journal of food protection Vol. 82; no. 2; pp. 194 - 199
• Main Authors: Limcharoenchat, Pichamon, James, Michael K, Marks, Bradley P
• Format: Journal Article
• Language: English
• Published: United States 01.02.2019
• Subjects: Colony Count, Microbial; Food Handling; Food Microbiology; Food Storage; Hot Temperature; Humans; Prunus dulcis - microbiology; Salmonella enteritidis - growth & development; Temperature; Pathogens; Nuts; Water activity; Thermal inactivation; Low moisture
• ISSN: 0362-028X; 1944-9097
• DOI: 10.4315/0362-028X.JFP-18-152

Salmonella survival and thermal resistance on the surface of almond kernels were evaluated after periods of storage. Almond kernels were inoculated with Salmonella Enteritidis PT 30 and equilibrated to 0.45 water activity. Samples were separated into two groups (I and II) and stored in sealed metal cans at room temperature. Group I samples (stored 7, 15, 27, and 68 weeks) were re-equilibrated in controlled humidity chambers to 0.45 water activity before performing the thermal treatments after each storage period, but group II samples (stored 70 and 103 weeks) were thermally treated immediately after the cans were opened. For thermal treatments, individual almond kernels were vacuum sealed in thin plastic bags, heated isothermally in a water bath (80°C) for nine intervals, immediately cooled in an ice bath, and assayed for surviving Salmonella. Log-linear and Weibull models were fit to the inactivation data. Salmonella population decreased ( P < 0.05) more than 2 log CFU/g during the long-term storage. Salmonella survival in group II at 70 weeks (7.3 log CFU/g) was higher ( P < 0.05) than in group I (which had been re-equilibrated multiple times) at 68 weeks (6.2 log CFU/g). However, the thermal resistance of Salmonella Enteritidis PT 30 did not decrease ( P > 0.05) for up to 68 weeks of storage, and the log-linear model best described the thermal inactivation data. Overall, the results suggest that re-equilibrating almonds (group I) multiple times may have increased the rate of reduction of Salmonella populations during long-term storage. However, Salmonella thermal resistance on almonds appears to be essentially unaffected by long-term storage, which is important information for designing and conducting validation studies for pathogen control processes.