Radiofrequency-assisted thermal processing for improving microbiological safety of low-moisture food powders

Low-moisture foods are traditionally considered as microbiologically safe foods. However, recent foodborne illnesses associated with consumption of low-moisture foods have heightened the concern of their microbiological safety. Thus, there is a critical need to pasteurize low-moisture foods. Traditional thermal processing methods are not suitable for pasteurizing these foods because of low thermal conductivity and high thermal resistance of the foodborne pathogens. In this study, a novel radiofrequency (RF)-assisted thermal processing method for pasteurization of two low-moisture food powders namely egg white powder (EWP) and soft wheat flour (SWF) was investigated. Based on the D and z values of Salmonella spp. in EWP and SWF, a few temperature and time combinations for the RF-assisted thermal processing were selected and evaluated in batch mode. The optimal temperature and time combinations based on quality and functionality were determined for each product. For EWP, the quality (color and solubility) and functional properties (foaming properties: foaming capacity and foam stability; and gelling properties: water holding capacity and gel-firmness) were investigated. Based on the quality and functionality, the optimal processing temperature and times for EWP were 90°C for 8 h or longer. The quality and functionality of SWF was investigated through chemical methods, Rapid-Visco-Analyzer profiles, and flour performance in sugar-snap cookies. Based on the quality and functionality, the optimal processing temperature and times for SWF were 80°C for 7 h or 90°C for 2 h.;The continuous RF-assisted thermal processing of EWP and SWF in packaging conditions was demonstrated experimentally. The package processed EWP at 80°C for 16 h exhibited excellent foaming and gelling properties as compared to that of the traditional and batch mode processed EWP. The important quality and functionality of the packaged SWF at 80°C for 7 h was not significantly different from that of the unpasteurized SWF. Thus, the RF-assisted thermal processing has shown great potential for thermal processing of low-moisture food powders by reducing the come-up time without compromising their quality and functionality. This study demonstrated a novel method to pasteurize low-moisture food powders. This study also determined the physical, thermal, and dielectric properties of EWP, which are important inputs for modeling RF heating. This helps further optimization of the electrode and food packaging configurations, which would further reduce the come-up time.