P1-170 Impact of Refrigerated Storage on Thermal Inactivation of Enterococcus faecium NRRL B-2354 and Salmonella Enteritidis PT 30 ATCC BAA-1045 on Inoculated Almonds

Monday, August 4, 2014
Exhibit Hall D (Indiana Convention Center)
Chris Theofel, University of California-Davis, Davis, CA
Linda Harris, University of California-Davis, Davis, CA
Introduction: Enterococcus faecium NRRL B-2354 is a recognized surrogate for Salmonella Enteritidis phage type 30 for thermal processes applied to almonds. Almond Board of California guidelines allow for surrogate-inoculated almonds to be stored at 3.3 to 4.4°C, but the impact of refrigerated storage on the thermal tolerance of E. faecium is unknown.

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.