Food Science and Technology Department


First Advisor

Curtis L. Weller

Second Advisor

David D. Jones

Third Advisor

Jeyamkondan Subbiah

Date of this Version

Spring 4-24-2020


A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Majors: Food Science & Technology and Biological Engineering, Under the Supervision of Professors Curtis L. Weller and David D. Jones. Lincoln, Nebraska: April, 2020

Copyright 2020 Soon Kiat Lau


The reputation of low-moisture foods as safe foods has been crumbling over the past decade due to repeated involvement in foodborne illness outbreaks. Although various pasteurization technologies exist, a majority are thermal processes and have not been well-characterized for pasteurizing low-moisture foods. In addition, the nature of a low-moisture food matrix introduces various experimental complications that are not encountered in high-moisture foods. In this dissertation, the development, building instructions, and characterization of various open source tools for studying the inactivation kinetics of microorganisms in low-moisture foods are described. The first tool is the TDT Sandwich, a dry heating device for measuring the thermal inactivation kinetics of microorganisms. The second tool is the HumidOSH, a self-contained environmental chamber for adjusting the water activity of food samples. Accompanying these tools are two studies that characterized the thermal inactivation kinetics of Salmonella and Enterococcus faecium NRRL-B2354 in whole milk powder and chia seeds. The TDT Sandwich was shown to produce thermal inactivation kinetics that are comparable with commonly used methods while also demonstrating less variation in microbial data collected with this tool. The comparison of model parameters using statistical tests of significance is discussed with the use of Monte Carlo simulations. E. faecium was shown to be a conservative surrogate to Salmonella in chia seeds. The variability between production lots of chia seeds was found to have a large impact on the inactivation kinetics of both Salmonella and E. faecium. The open source tools presented in this dissertation and the accompanying conclusions of the thermal inactivation studies can be used to accelerate scientific progress in understanding and improving the microbiological safety of low-moisture foods.

Advisers: Dr. Curtis L. Weller and Dr. David D. Jones