Graduate Studies
Embargoed Master's Theses
First Advisor
Byron D. Chaves
Committee Members
Jordan Wicks, Gary Sullivan
Date of this Version
8-2025
Document Type
Thesis
Citation
A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science
Major: Animal Science
Under the supervision of Professor Byron D. Chaves
Lincoln, Nebraska, August 2025
Abstract
The production of safe, shelf-stable beef jerky requires validated thermal processes capable of consistent pathogen reduction, particularly against Salmonella. This study evaluated the effects of beef portion thickness, drying temperature, and contamination route on Salmonella survival kinetics during dehydration and storage. The objective was to inform HACCP strategies and support compliance with USDA-FSIS lethality guidelines.
Beef eye of round slices were cut into three thicknesses (0.38, 0.64, 0.95 cm), inoculated with a five-serovar Salmonella cocktail via direct immersion or spice mix marinade, and dried at 154 °F (68 °C) or 160 °F (71 °C) using a home-style dehydrator. Water activity (aw) was monitored hourly. Salmonella counts were measured over a 6-hour drying period and at Days 7 and 14 post-dehydration. A factorial design assessed the impact of treatment combinations on lethality and shelf-stability.
Product thickness significantly influenced time to reach aw ≤ 0.85 (p = 0.0144), with thicker slices requiring longer drying times. Thickness and drying time significantly affected microbial log reductions, while temperature and inoculation method did not independently impact lethality. After 6 hours, all treatments achieved > 6-log CFU/g reductions, surpassing the USDA-FSIS benchmark for ready-to-eat jerky. However, Salmonella was still detectable (up to 3 log CFU/g) after 14 days of ambient storage, indicating its desiccation tolerance and potential for long-term survival.
To model microbial survival kinetics, several non-linear inactivation models were evaluated. The Weibull model with residual population (Albert & Mafart, 2005) best described the data, capturing both shoulder and tail phases of microbial death curves. It achieved an average Acceptable Prediction Zone (APZ) of 94.05%, adjusted R2 of 0.96, and low RMSE of 0.26, indicating high predictive accuracy.
In summary, drying alone can provide sufficient lethality when properly controlled, but slice thickness, real-time aw monitoring, and predictive modeling are crucial for effective process validation. The results support improved process control and the potential need for post-lethality interventions to ensure jerky safety, particularly for small and very small processors striving for USDA-FSIS regulatory compliance.
Advisor: Byron D. Chaves
Comments
Copyright 2025, Kassim Wachiebine Sulleyman. Used by permission