Food Science and Technology Department


First Advisor

Jeyamkondan Subbiah

Second Advisor

Terry Howell Jr.

Date of this Version

Spring 4-22-2021


Verma, T. (2021). Process Interventions for Improving the Microbiological Safety of Low Moisture Food Ingredients. Ph.D. Dissertation, University of Nebraska-Lincoln.


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, Under the Supervision of Professors Jeyamkondan Subbiah and Terry Howell Jr. Lincoln, Nebraska: April, 2021.

Copyright 2021 Tushar Verma


The recurrence of Salmonella in low moisture foods and the implementation of the FSMA rule requires a need to validate legacy and novel processing technologies. In this dissertation, a legacy thermal (extrusion), a novel thermal (radiofrequency (RF) heating), and a non-thermal (chlorine dioxide) technology, were evaluated as intervention technologies for Salmonella in low moisture foods. The twin-screw extruder was performed at different levels of screw speeds, temperatures, moisture contents, and fat contents to understand the impact of processing conditions on Salmonella inactivation in oat flour. At temperature >65°C, the Salmonella population was below the detection limit. At 55°C, Salmonella reduction ranged from 0.0 to 9.0 log CFU/g. A response surface model developed for mean residence time (MRT) showed that temperature had no significant effect, whereas screw speed, moisture content, and fat content had a significant linear effect on the MRT. On replacing the screw speed with MRT in the previously developed microbial inactivation models, the R2 value for Salmonella and Enterococcus faecium NRRL B-2354 increased slightly from 0.83 to 0.85 and 0.84 to 0.89, respectively. As MRT is challenging to measure, a slight improvement in the accuracy of the models does not warrant the use of MRT in the inactivation models. The thermal inactivation kinetics of Salmonella and E. faecium was determined in dried basil leaves using a dry heating method. As the water activity and temperature increased, the D-value of both microorganisms decreased. During RF heating, the inoculated sample was placed in the identified cold spot and was heated for 45, 55, 65 s. Both microorganisms were below the detection limit at 65 s without significantly affecting the quality of dried basil leaves. The results from the chlorine dioxide gas treatment showed that as the gas concentration and relative humidity increases, the D-value of both microorganisms decreases. The results presented in this dissertation can help the food industries in planning in-plant validation studies for improving the microbial safety of low moisture foods.

Advisors: Drs. Jeyamkondan Subbiah & Terry Howell Jr.