Purpose: To assess the survival and thermal resistance of E. faecium and Salmonella Enteritidis on inoculated almonds during refrigerated storage.
Methods: E. faecium and Salmonella Enteritidis were harvested from agar lawns and then inoculated onto almonds; air-dried inoculated almonds were stored at 4 ± 2°C for up to 12 weeks. Inoculated almonds (n = 6, from two trials) were sampled at bi-weekly intervals and were treated at 138 ± 2°C for 15 min in either a gravity feed or forced air (E. faecium only) oven on aluminum mesh trays. The hot almonds were immediately transferred to cold tryptic soy broth and shaken, stomached, and serially diluted in Butterfields phosphate buffer before plating onto tryptic soy agar (Enterococcus and Salmonella) and bismuth sulfite agar (Salmonella).
Results: Populations of E. faecium and Salmonella Enteritidis on almonds did not significantly decrease throughout 12 weeks of refrigerated storage. At all time points, reductions of Salmonella Enteritidis were 2.7 ± 0.1 log CFU/g upon heat exposure in the gravity feed oven. In contrast, reductions of E. faecium increased steadily from 1.5 log CFU/g at time 0 to 2.3 log CFU/g at week 12, and differences were significant between weeks 0 and 1 and week 12. Reductions of E. faecium were significantly (P < 0.05) higher in the forced air oven than in the gravity feed oven.
Significance: Further research is necessary to support long-term storage of E. faecium-inoculated almonds for validation studies.