Recent outbreaks and recalls of low-moisture foods contaminated with Salmonella have been recognized as a major public health risk that demands the development of new Salmonella mitigation strategies and technologies. This study aimed to assess the efficacy of X-ray irradiation for inactivating Salmonella on or in almonds (kernels, meal, butter), dates (whole fruit, paste), and wheat (kernels, flour) at various water activities (aw) and storage periods. The raw materials were inoculated with Salmonella Enteritidis PT30, conditioned to 0.25, 0.45, and 0.65 aw in a humidity-controlled chamber, processed to various fabricated products, and reconditioned to the desired aw before treatment. In a storage study, inoculated almond kernels were stored in sealed tin cans for 7, 15, 27, and 103 weeks, irradiated with X ray (0.5 to 11 kGy, targeting up to a ∼2.5-log reduction) at the end of each storage period, and plated for Salmonella survivors to determine the efficacy of irradiation in terms of D10-value (dose required to reduce 90% of the population). Salmonella was least resistant (D10-value = 0.378 kGy) on the surface of almond kernels at 0.25 aw and most resistant (D10-value = 2.34 kGy) on the surface of dates at 0.45 aw. The Salmonella D10-value was 61% lower in date paste than on whole date fruit. Storage of almonds generally had no effect on the irradiation resistance of Salmonella over 103 weeks. Overall, these results indicate that product structure (whole, meals, powder, or paste), water activity (0.25 to 0.65 aw), and storage period (0 to 103 weeks) should be considered when determining the efficacy of X-ray irradiation for inactivating Salmonella in various low-water-activity foods.

Outbreaks and recalls associated with microbial contamination of powdered foods have raised concern for the safety of the spray drying process and its products. However, little research on the fate of bacteria during the spray drying process has been done, leaving much unknown about the risks of contamination in spray dryers. Therefore, quantifying the contamination levels of  Salmonella  and  Enterococcus faecium  (as a surrogate) in various locations within a pilot scale spray dryer can help illustrate the distribution of bacterial contamination, including the final product. A 10% w/w dispersion of water and soy protein isolate was mixed with tryptic soy broth containing yeast extract inoculated with  Salmonella  Enteritidis phage type 30 ( S.  Enteritidis PT30) or  E. faecium  NRRL B-2354. This dispersion was spray dried using a pilot scale tall-form co-current spray dryer at inlet air temperatures of 180, 200, or 220°C. After drying, samples of powder from 8 locations within the system were collected/surface swabbed, plated, and enumerated. Spray drying achieved 2.40-4.15 and 2.33-2.83 log reductions in concentration of  Salmonella  and  E. faecium,  respectively in the final powder product accumulated in the dryer’s collectors.  Salmonella  and  E. faecium  were found in varying concentrations in all locations within the spray dryer after a complete drying cycle. Differences in inlet air temperature between 180-220°C had no significant effect on the inactivation levels. As a surrogate,  E. faecium  was more resistant to spray drying than  Salmonella . Overall, spray drying is capable of significant bacterial reduction in the final powder product, which can be combined with other hurdle technologies. However, adequate cleaning and sanitization procedures must be taken into considerations to prevent cross-contamination.