Food Science and Technology Department


First Advisor

Jeyamkondan Subbiah

Second Advisor

Jayne Stratton

Date of this Version



Vasquez, 2018


A THESIS Presented to the Faculty of The Graduate College at 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 Jayne Stratton. Lincoln, Nebraska: August 2018

Copyright (c) 2018 Sabrina Vasquez


Food safety concerns of low-awfoods have boosted, given the increased number of foodborne illnesses related to these products. Black pepper, among other spices, has been implicated in several outbreaks and recalls in recent years.Salmonella entericahas been identified as the causing agent of outbreaks of contaminated spices. Therefore, increased efforts should be conducted to ensure food safety of spices, including black pepper. Food Safety Modernization Act (FSMA) demands all food processing facilities to conduct proper validations of the decontamination technologies applied to food products. Complete thermal process validations require a deep understanding of the thermal inactivation kinetics of the pathogen identified in risk assessments. The objectives of this study were to validate a novel dry heating method, thermal-death-time (TDT) sandwiches, for determination of thermal inactivation kinetics of Salmonellaspp. and E. faeciumNRRL B-2354 in ground black pepper and to evaluate the effect of water activity on the thermal resistance of these microorganisms. Black pepper samples were inoculated with a 5-strain cocktail of Salmonellaor E. faecium and equilibrated to the target water activity prior to thermal inactivation. D- and z-values were determined for 0.45 awat different heating rates and treatment temperatures using TDT sandwiches. Conventional heating method for thermal inactivation kinetics determination, TDT test cells, were used to compare D-value results with those obtained using TDT sandwiches for 0.45 awsamples. TDT sandwiches demonstrated to have operational benefits compared to TDT cells including lower log reductions during Come-up time, use of disposable sterile aluminum pouches with higher sample capacity, adjustable heating rates and dry heating method that eliminate possibility of leakage during treatment. Thermal resistance of Salmonella spp. in black pepper equilibrated to 0.45 awwas influenced by the method used, whereas, the thermal resistance of E. faeciumwas not. Heating rates above 6.5 °C/min using TDT sandwiches did not change the D-values of both microorganisms at all temperatures evaluated. Later, TDT sandwiches were used at 600 °C/min for thermal inactivation of inoculated black pepper at 0.25 and 0.65 aw.D- and z-values were also determined for these conditions. Response surface equations for log D-value determination of E. faeciumand Salmonella spp. were developed.

In this study, TDT sandwiches were validated as a novel dry heating method for determination of thermal inactivation kinetics ofSalmonellaspp. and E. faeciumin ground black pepper. Salmonella’s and E. faecium’s D-values at 75 °C for 0.25 awsamples were 42.86 min and 58.35 min, respectively. These D-values decreased to 1.51 min forSalmonellaspp. and 4.56 min for E. faeciumfor 0.65 awsamples, at the same temperature. Furthermore, independent of the heating method used and for samples conditioned to 0.25. 0.45 and 0.65 aw, E. faeciumwas identified as a suitable surrogate for Salmonellaspp. in ground black pepper.

Advisors: Jeyamkondan Subbiah & Jayne Stratton