Date of Graduation

5-2024

Document Type

Thesis

Degree Name

Master of Science in Food Science (MS)

Degree Level

Graduate

Department

Food Science

Advisor/Mentor

Acuff, Jennifer C.

Committee Member

Subbiah, Jeyamkondan

Second Committee Member

Villa Rojas, Rossana

Keywords

Enterococcus faecium; Low moisture food; Mild heating; Ozone; Relative humidity; Salmonella

Abstract

Due to the increasing number of reported outbreaks of pathogens in low-moisture foods (LMFs), there is a need to investigate novel non-thermal gaseous technologies to increase the microbiological safety of spices, nuts, and seeds without compromising the product quality. The objective of this study was to inactivate Salmonella spp. in different spices, seeds, and nuts using gaseous ozone treatment and evaluate the suitability of Enterococcus faecium as a potential surrogate for Salmonella. Each food product (dried basil leaves, black peppercorn, chia seeds, and walnuts) was separately inoculated with a 5-strain Salmonella and E. faecium cocktail and equilibrated to water activity (aw) of 0.55. Two-gram samples of inoculated foods were treated with ozone concentrations of 900-930 ppm at relative humidity (RH) of 70-90% within a test chamber for predetermined time intervals of 1-5 h, followed by mild heating at 40℃ for 4 h. Treatment comparisons of means of log reductions of each product for microbial inactivation were performed in JMP Pro 16 software at the significance level of 5%. At ozone concentration of 900-930 ppm and RH of 90%, the 5 h ozone treatment resulted in maximum log CFU/g reductions of 5.0 ± 0.4 for basil, 2.5 ± 0.2 for black pepper, 1.1 ± 0.1 for chia seeds, and 1.5 ± 0.2 for walnuts. There was no significant difference between 1 h and 5 h ozone treatment for chia seeds and walnuts (p<0.05). Post-treatment mild heating at 40ºC for 4 h further significantly inactivated Salmonella by 1-1.5 log CFU/g for black pepper and dried basil, but not for walnuts and chia seeds. E. faecium was a good surrogate for Salmonella just for basil leaves treated with gaseous ozone at 90% RH. With lower R2 and RMSE values, the Weibull model fit data better than log-linear model. There was no significant impact of gaseous ozone treatment on color, antioxidants, and total phenolics of the 4 LMFs. However, 5 h ozone treatment caused significant loss in a few minor volatile compounds of dried basil leaves, and black peppercorn and increased the primary and secondary oxidation products in walnuts. The results of this study indicate the potential of using the synergistic effect of gaseous ozone, relative humidity, and mild heating to improve the microbial safety of spices and nuts during storage.

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