"Foodborne illness outbreaks linked to spray dried foods like infant formula and protein powders demonstrate a need for greater understanding of bacterial inactivation kinetics during spray drying. However, despite extensive research regarding the mechanisms of the spray drying process, the survival of bacteria during spray drying is not well understood. Therefore, the objectives were to: (1) measure the inactivation rates of Salmonella within a spray drying droplet, (2) develop a model that relates droplet drying kinetics to Salmonella inactivation rate, and (3) assess the survivability of Salmonella and Enterococcus faecium throughout a pilot-scale spray dryer. In the first study, a thin layer of soy protein slurry inoculated with Salmonella was dried in a convection oven using actual spray drying conditions to measure the inactivation rate of Salmonella within droplets. Thereafter, a heat-mass coupled droplet drying model and secondary bacterial inactivation models using droplet temperature and moisture content were developed. Lastly, the survival and spatial distribution of Salmonella and Enterococcus faecium throughout a pilot-scale spray dryer were evaluated at various process temperatures. Bacterial inactivation rate was successfully modeled, with the best fitting secondary model including parameters for both droplet temperature and moisture content, which were coupled with the droplet drying model and validated. Although the spray drying process was able to reduce both organisms, survivors were found both in the final powder as well as the interior dryer surfaces, which indicates a potential health risk if the spray dryer is contaminated."--Page ii.
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