Food Science and Technology Department


First Advisor

Jeyamkondan Subbiah

Second Advisor

Mary-Grace Danao

Date of this Version

Spring 4-22-2021


Wei, X. (2021).Microbial Challenge Studies of Radio Frequency Heating for Dairy Powders and Gaseous Technologies for Spices. 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 Mary-Grace Danao. Lincoln, Nebraska: April 2021.

Copyright © 2021 Xinyao Wei


Persistence, thermal resistance, and survival of Salmonella in low moisture foods (LMF) have resulted in several foodborne illness outbreaks. Both existing and novel pasteurization technologies need to be validated for microbial safety of LMF. In this dissertation, a framework for using radio frequency (RF) heating to enhance microbial safety of milk powders and egg white powder was established. Thermal inactivation kinetics of Salmonella in milk powders were determined to guide the dairy industry for identifying thermal processing conditions for pasteurization. Storage time showed no effect on the thermal resistance of Salmonella, which can simplify the process validation study in the industry. Hot air-assisted RF heating followed by holding at high temperatures in a convective oven was developed and validated for pasteurization of milk powders. Continuous RF processing was evaluated for pasteurization of egg white powder (EWP), which can provide> 6.7 log reduction for Salmonella after RF-assisted thermal processing of EWP at 80°C for 2 h. Ethylene oxide (EtO) and chlorine dioxide (ClO2) gaseous technologies were evaluated as non-thermal pasteurization for improving microbial safety of spices. A response surface model was developed as a function of temperature, relative humidity, and exposure time to predict the reduction of Salmonella or Enterococcus faecium NRRL B-2354 on whole black peppercorn during EtO fumigation, which can guide the spice industry in determining the process conditions for pasteurization. The effects of gas concentration, RH, and exposure time on Salmonella and E. faecium on whole black peppercorn and cumin seeds during ClO2 gaseous treatment were evaluated which can provide technical information for implementation of this technology. E. faecium was found to be a suitable surrogate for Salmonella during both thermal (RF) and non-thermal (EtO and ClO2) of dairy powders and spices, respectively. Therefore, the food industry can use E. faecium to replace Salmonella for conducting the industrial process validation.

Advisors: Drs. Jeyamkondan Subbiah and Mary-Grace Danao