Radiofrequency pasteurization against Salmonella and Listeria monocytogenes in cocoa powder

In this study, thermal processes were developed for cocoa powder against Salmonella and Listeria monocytogenes in a pilot Radiofrequency (RF) unit and validated using their respective surrogates Enterococcus faecium NRRL B2354 and Listeria innocua. For 1.0 kg cocoa powder samples, RF heating to 90 degrees C provided 1.74-1.84 log reduction of E. faecium. A 48 min holding post-RF heating provided an additional 3.65 and 2.24 log10 CFU/g reduction of E. faecium for insulated and non-insulated samples, respectively. Compared to E. faecium, L. innocua was less resistant to RF heating in aw 0.45 cocoa powder; RF heating to 75 degrees C coupled with 24 min insulated holding resulted in an additional 5.64 log10 CFU/g reduction. These data suggested that E. faecium was a conservative surrogate strain for controlling Salmonella and L. monocytogenes during RF processing of cocoa powder. To achieve maximal microbial reduction and improve energy efficiency, an insulated holding following RF heating is highly recommended. According to the predictive line obtained from the Bigelow model, a 7.6 min RF heating plus 48 min insulated holding attained a 5-log reduction of E. faecium without a negative impact on the color of cocoa powder.