Assessment of Home-Scale Heat Treatment for Reducing Salmonella in Multiple Flours

Public awareness of the risks of raw flour consumption has increased in recent years. Consumers and various organizations have created online resources that offer home-scale solutions claimed to reduce pathogens in raw flour. The objective of this study was to test the efficacy of such treatments for reducing Salmonella in a variety of flours. An online search for home-scale instructions for flour heat treatment informed the experimental design. All-purpose, whole-wheat, and gluten-free varieties of flour were inoculated with Salmonella Enteritidis PT 30 (∼8.65 log CFU/g) and conditioned to a water activity of ∼0.45 for ≥2 days. Samples (three biological replications with triplicate subsamples) were spread into a uniform layer ∼0.5 cm thick, heat-treated in a home-scale oven at 177 °C up to 10 min (based on the analysis of consumer-focused sources), then transferred to sterile bags, cooled, serially diluted, and plated on differential media. Transient flour temperature and a_w were recorded. A summary of data sourced from the selected consumer-oriented webpages was created to contextualize disseminated claims of risk from flour consumption. After a 10 min treatment, Salmonella log reductions (mean ± standard deviation) were 3.28 ± 0.52 (all-purpose), 4.09 ± 0.46 (whole-wheat), and 4.13 ± 0.67 (gluten-free). Similar a_w trends were observed for all flour products, with values <0.1 after 7.5 min. Mean Salmonella reductions in all products were less than 5 log after a 10 min treatment (p < 0.05). There was less (p < 0.05) Salmonella reduction in all-purpose flour than in whole-wheat and gluten-free flour. None of the home-scale solutions evaluated in this study were scientifically supported by the results of this study to achieve a nominal 5 log reduction of Salmonella. Extended thermal treatment times also impacted the visual quality of the flour. Although the thermal treatments reduced Salmonella, it is unknown whether this is sufficient or best practice for consumers.