Food Science and Technology Department


First Advisor

Jeyamkondan Subbiah

Second Advisor

Andreia Bianchini

Date of this Version



Verma et al. (2017). Validation of Extrusion Processing for the Safety of Low-Moisture Foods (M.S. Thesis).


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: Food Science and Technology, Under the Supervision of Professors: Jeyamkondan Subbiah and Andreia Bianchini. Lincoln, Nebraska: August, 2017

Copyright (c) 2017 Tushar Verma


Salmonella in low-moisture foods is an emerging challenge due to numerous food product recalls and foodborne illness outbreaks. The new Food Safety Modernization Act requires the food processors to validate their process controls that indeed kills the desired number of bacteria. This research had two major objectives: 1) Develop a response surface model for Salmonella inactivation during the extrusion of low-moisture food 2) Evaluate the use of Enterococcus faecium NRRL B-2354 as an adequate surrogate for Salmonella during the extrusion of low-moisture food. Oat flour was selected as a low-moisture food model. For inoculation, cocktail of five different strains of Salmonella was used and Enterococcus faecium NRRL B-2354 was used as a potential surrogate for Salmonella. The inoculated samples were adjusted to different moisture (14 to 26%) and fat levels (5 to 15%) that were then extruded in a single-screw extruder running at different temperatures (65 to 85˚C for Salmonella; 75 to 95˚C for E. faecium) and screw speeds (75 to 225 rpm). A split-plot central composite 2nd order response surface design was used, with central points replicated six times. Temperature showed the highest significant effect on Salmonella (p < 0.0001) and E. faecium (p < 0.0001) reduction. Moisture content showed a significant quadratic effect on Salmonella (p = 0.0005) reduction and linear and quadratic effect on E. faecium (p = 0.0002) reduction. Fat content showed a significant protective effect on Salmonella (p < 0.0001) reduction, whereas fat content had a significant interactive effect with moisture on E. faecium (p < 0.0001) reduction. The screw speed had a significant interactive effect with the temperature on Salmonella (p = 0.0004) reduction, whereas it had a linear effect on E. faecium (p < 0.0001) reduction. The results showed that both microorganisms showed a different response depending upon fat, moisture content, and screw speed. However, temperature showed a similar effect on both the microorganisms when thermal inactivation was considered. The reduction of E. faecium was always lower than the one obtained for Salmonella under similar conditions. Therefore, E. faecium may be an acceptable surrogate for Salmonella due to its higher thermal resistance.

Advisors: Jeyamkondan Subbiah & Andreia Bianchini