Radio frequency-only thermal processing of skimmed milk powder: Case study on the influence of RF heating profile on quality and Salmonella Typhimurium inactivation

Abstract

Radio frequency (RF) is a dielectric heating technology that allows rapid and volumetric heating of milk powder, outperforming the heating uniformity of conventional powder heating methods. Typically, RF milk powder processing consists of a fast RF heating phase, followed by an oven heating phase in temperatures around 90 °C. This methodology can result in milk powder quality deterioration due to non-uniform temperature distributions and local overheating. Radio frequency-only processes with a more gradual heating rate are alternative solutions to minimise the impact on milk powder quality. This study investigated the effect of the heating rate on the microbial inactivation of Salmonella Typhimurium inoculated in skimmed milk powder, as well as the effect of each process on two quality characteristics, colour and solubility. Overall, a slower heating profile resulted in sufficient inactivation rates of Salmonella in skimmed milk powder, while still providing a high-quality end product. A 4-log reduction was achieved by treating the skimmed milk powder up to 95 °C using a slower, longer heating rate. No statistically significant changes were observed in the solubility of skimmed milk powder and only the harshest treatment to 95 °C led to a slight increase in the yellowness of the skimmed milk powder colour.