Assessment of radio frequency heating on composition, microstructure, flowability and rehydration characteristics of milk powder

Radio frequency inactivation of Salmonella Typhimurium and Listeria monocytogenes in skimmed and whole milk powder

Milk powder is a convenient, shelf-stable food ingredient used in a variety of food products. However, pathogenic bacteria can be present and survive during prolonged storage, leading to outbreaks of foodborne diseases and product recalls. Radio frequency (RF) heating is a processing technology suitable for bulk treatment of milk powder, aiming at microbial inactivation. This study investigates the RF inactivation of Salmonella Typhimurium and Listeria monocytogenes in two types of milk powder; skimmed and whole milk powder. Specifically, the aims were to (i) examine the influence of the powder's composition on bacterial inactivation, (ii) evaluate the response of bacteria with different Gram properties (Gram positive and Gram negative) and (iii) verify the use of Enterococcus faecium as a surrogate for the two microorganisms for the specific RF process. In order to examine exclusively the influence of RF, a non-isothermal temperature profile was used, employing solely different RF energy levels to heat the product to the target temperatures. A log-linear model with a Bigelow-type temperature dependency was fitted to the experimental data. S. Typhimurium was less susceptible to RF treatments in comparison to L.monocytogenes, demonstrating a higher inactivation rate (k) and higher percentage of sublethal injury. A higher k was also observed for both microorganisms in the whole milk powder, indicating that the increased fat content and decreased levels of lactose and protein in the milk powder had an adverse impact on the microbial survival for both pathogens. The surrogate microorganism E. faecium successfully validated the microbial response of the two microorganisms to RF treatments. In general, a low heating rate RF-only process was successful in inactivating the two foodborne pathogens in skimmed and whole milk powder by 4 log(CFU/g).

Radio Frequency Heating of Milk–Effects on Quality, Safety, and Shelf Life Assessed Using Artificial Senses and Chemometric Tools

Thermal treatments are widely-used strategies in the food industry to inactivate microorganisms and enzymes in order to guarantee safe products without the need for preservatives, while still prolonging their shelf life. Commercial sterilization usually relies on pressurized hot water or steam, often leading to long process times and to surface dehydration phenomena and overheating. However, from the recent studies in the field of radio frequency heating, it has emerged that food products can be processed with time-temperature regimes that are much milder than those required with conventional techniques, resulting in minimal modification of the sensory and nutritive attributes of the food product itself. In the present work, raw bovine milk was sterilized through a combination of steam and radio frequencies, at various temperatures. Alongside the chemical composition, the pH, acidity, and total mesophilic count have been evaluated before and after the process and at the different exit temperatures, in order to study the impact of this technique on milk quality and safety aspects, during a storage period of 55 days at +4°C. Moreover, the organoleptic properties of milk have been studied using artificial senses coupled with chemometrics. Different temperatures lead to homogenous physicochemical and microbiological results, which conform to those expected for a good quality bovine milk. The assessment of flavor and appearance revealed retained or the minimally modified milk sensorial properties. Therefore, RF heating appears to be a suitable technique for the production of safe milk with a prolonged shelf life up to 40–45 days and without significant alterations of the organoleptic and nutritional attributes.