Heat-load–guided microbial decontamination of wheat flour and grains: Balancing safety and baking performance across vacuum steam, microwave, and radio-frequency treatments

Wheat flour is microbiologically stable due to low aw, but pathogens like Salmonella and Shiga toxin–producing Escherichia coli can persist, posing risks in products lacking adequate heat treatment. Conventional high-temperature processing is unsuitable, because it impairs flour functionality for baking. This study compared the effectiveness of three thermal technologies, vacuum steam (VS), microwave (MW), and radio frequency (RF), for microbial inactivation in wheat grain and flour, while assessing impacts on flour functionality. Enterococcus faecium NRRL B-2354, a surrogate for Salmonella, was used to evaluate microbial reduction. Treatments were conducted at temperatures from 55 °C to 95 °C with holding times of 5–13 min. Heat loads (HL) calculated from measured temperature-time profiles during treatments were used to compare effects across technologies. Flour functionality was evaluated based on free sulfhydryl group (free-SH) content, pasting properties, starch gelatinization behaviour, and bread volume. HL ≤ 11 k°C·s enabled to achieve 3–6 log reduction of E. faecium in flour compared to 1–2.5 in grain, with VS showing generally higher reductions for similar HL compared to MW and RF. Flour functionality (i.e. free-SH, pasting properties and bread volume) were also a function of the applied HL, with gluten aggregation being the main mechanism. Overall, HL emerged as a valuable metric to compare effects of the different technologies and temperature-time conditions. This result allowed to identify heat load conditions to achieve 3–6 log reduction of E. faecium, while preserving flour functionality. Low temperatures (i.e. 55–65 °C) applied for few minutes emerged as promising treatment conditions across technologies.