Evaluation of Enterococcus Faecium Nrrl B-2354 as Surrogate for Salmonella for Pasteurization Processes of Raisin

Introduction:  Salmonella is one of the major foodborne bacterial pathogens. It has been associated with outbreaks of low moisture products. Food facilities are required to implement and document that their preventive controls are working and verified. The use of pathogenic microorganism in plant environment may pose an unacceptable risk.

Purpose: The objective of this study was to evaluate Enterococcus faecium NRRL B-2354 as a potential thermal surrogate organism for Salmonella for in-plant validation studies of raisin.

Methods:  E. faecium NRRL B-2354 and Salmonella were streaked onto Tryptic Soy Agar (TSA) and harvested using 0.1% peptone. Raisin samples (400 ± 1 g) were inoculated with 25 ml of the pooled inocula. Inoculated raisins were stored for up to 72 hr at 24 ± 2ºC to let them dry. Inoculated raisins were heat treated in an isotemp oven at 180°F.

Results: The thermal inactivation rates of Salmonella and E. faecium NRRL B-2354 were compared. The counts of E. faecium NRRL B-2354 were reduced by 0.6 log after 14 min and 3.3 log after 28 min at 180°F. The thermal reductions values for Salmonella were 1.4 log after 14 min and 6.1 log after 28 min at 180°F.

Significance: The data showed that E. faecium NRRL B-2354 was 1.4 times more heat resistant than Salmonella in raisin and could be used as a nonpathogenic surrogate for in-plant trials.