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

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 <i>Salmonella</i> 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 <i>Salmonella</i> 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.