Inactivation kinetics for Salmonella typhimurium in red pepper powders treated by radio frequency heating

Radio frequency (RF) dielectric heating has been investigated to inactivate pathogens in some low-moisture foods. This study was aimed to evaluate RF inactivation effects on Salmonella typhimurium in red pepper powders, by focusing on the influence of sample initial water activity (a_w) and applying Weibull model to describe the inactivation curves. The experimental results showed that RF heating rate increased when a_w was in the range of 0.57–0.71, but decreased after a_w reached to 0.71. During the come-up time of RF heating, 2–3 log reduction of the pathogen was achieved depending on a_w levels. Increasing initial a_w could first increased log reductions and then decreased the log reductions, optimum a_w level was 0.71 for RF inactivation of Salmonella in red pepper powders. For red pepper powders with a_w of 0.71, RF heating to 70 °C (come-up time was 110 s) with holding time over 60 s could achieve >5 log reduction of S. typhimurium. Weibull model well fitted the survival curves of the pathogen with goodness of fit (R² > 0.93, RMSE<0.29). Scale factor (b) of the model increased with treatment temperature increasing, while the shape factor (n) was independent on temperature. This study provided basic guideline for using RF heating to inactivate Salmonella in red pepper powders.