Effect of Radio Frequency on the Reduction of Enterococcus faecium in Raw Peanuts

Introduction: Multiple outbreaks of salmonellosis have been associated with the consumption of low-moisture products, including peanuts and peanut butter. Enterococcus faecium has already been used in the evaluation of oil and dry roasting processes of peanuts as a surrogate for Salmonella. Alternative technologies like radio frequency (RF) are being used for nut roasting and shelled almond pasteurization. Therefore, scientific information on the effect of RF processing on E. faecium reduction in raw shelled peanuts treated is needed.

Purpose: The goal of this research was to determine the level of E. faecium NRRL B-2354 reduction in runner-type peanuts treated with RF technology.

Methods: Product (1,000 g) was inoculated (~7 log CFU/g) with E. faecium NRRL B-2354 using dry inoculation.  Inoculated peanuts were packed in 25 g aliquot in nylon bags. A box (11 lbs) holding three bags, located in the coldest area, was placed at center of the cavity of the RF system and treated until the target temperature was achieved. Peanuts were RF treated (27 MHz) at 3 temperatures, ≥85°C, ≥110°C and ≥126°C, with three different process times. Each temperature and time was evaluated in triplicate. After each treatment, the pouches were immediately cooled in ice and plated.

Results: RF treatment produced <2.0 log CFU/g reduction of E. faecium at ≥85°C, and ≥5.0 log CFU/g reduction at ≥110°C and ≥126°C.

Significance: The significance of this study is that a 5 log CFU/g reduction of E. faecium in raw peanuts with RF processing was achieved at temperatures lower than oil (120 to 160°C) and dry (129 to 163°C) roasting.