Author ORCID Identifier

https://orcid.org/0000-0002-6935-1576

Semester

Summer

Date of Graduation

2025

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Animal and Nutritional Sciences

Committee Chair

Cangliang Shen

Committee Member

Jacek Jaczynski

Committee Member

Annette Freshour

Committee Member

Timothy Boltz

Abstract

This dissertation investigates the efficacy of Enterococcus faecium as a surrogate for Salmonella in validating thermal inactivation processes during poultry feed manufacturing and meat processing. The research encompassed three studies evaluating microbial kinetics in mash broiler feed, reconstructed ground chicken, and predictive modeling approaches to improve food safety interventions. In the first study, the thermal resistance of nalidixic acid-resistant Salmonella Typhimurium and E. faecium was compared in mash broiler feed heated at 75–95°C. Results demonstrated that E. faecium exhibited significantly greater heat resistance than Salmonella, with longer shoulder times, greater tailing effects, and higher D-values, supporting its use as a conservative surrogate for validating feed pelleting processes. The second study examined the effects of temperature and salt concentrations on the thermal inactivation of both microorganisms in reconstructed ground chicken meat. Heating at 62–74°C revealed that increased salt levels enhanced Salmonella’s thermal resistance at lower temperatures but reduced survival at higher temperatures. Across all treatments, E. faecium consistently showed higher resistance, reinforcing its suitability as a surrogate. Machine learning models, including Random Forest and Support Vector Regression, effectively predicted microbial reductions, highlighting temperature and exposure time as the most critical factors influencing inactivation. Collectively, these findings provide robust evidence that E. faecium can serve as a reliable, conservative surrogate for Salmonella in both poultry feed and meat products. The kinetic models and predictive tools developed herein offer the poultry industry practical guidance for designing and validating thermal processing interventions aimed at reducing foodborne pathogen risks and enhancing consumer safety.

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