Theses and Dissertations

Date of Award

8-2023

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biochemistry and Molecular Biology

First Advisor

Veerachandra Kranti Yemmireddy

Second Advisor

Ahmed Touhami

Third Advisor

Manohar Chakrabarti

Abstract

World-wide consumption of fresh-cut produce has seen a dramatic increase over the past few decades. However, fresh-cut produce has been implicated in several illness outbreaks due to contamination with foodborne bacterial pathogens. Post-harvest contamination during handling and processing is considered rare but several influencing factors are often overlooked. Specifically, studies have reported the growth, survival, and death kinetics of foodborne bacterial pathogens such as E. coli O157: H7, Salmonella and Listeria monocytogenes in different fresh and fresh-cut produce. The effect of various factors such as storage temperature, time, and relative humidity are widely explored. It is increasingly evident that microbial pathogens are naturally exposed to various environmental stresses in the farm to fork continuum. The nature of stresses and their response to these stresses determine the likelihood of risk. Limited knowledge exists in understanding the effect of environmental stresses on the growth and survival kinetics of foodborne pathogens. Thus, this thesis research mainly focused on understanding the effect of select environmental stresses on survival kinetics of Salmonella enterica and L. monocytogenes. A study was conducted to determine the effect of different pre-growth temperatures (4, 21, and 37 ºC) on survival kinetics of S. enterica and L. monocytogenes in fresh-cut salad during simulated retail or consumer refrigerated storage at 4 ºC and 80 % RH. Pre-growth temperature(s) and the type of produce showed a significant (p≤ 0.05) effect on the survival kinetics of L. monocytogenes during the storage. Among the tested produce, mixed salad and shredded carrot showed the highest reduction of L. monocytogenes and S. enterica, respectively. Baranyi and Roberts model better fitted the experimental data (R2; 0.054 to 0.967 for L. monocytogenes, and 0.194 to 0.994 for S. enterica). Another study was conducted to determine the effect of pre-growth environmental conditions (4 and 37 ºC, pH 4.5) on L. monocytogenes response to different antimicrobial light (UVC, UVA, blue light) treatments. As expected, increasing the treatment time increased the log reductions. Under the tested conditions pre-growth stresses did not show a significant (P>0.05) effect on the L. monocytogenes. These findings indicate that appropriate selection of pre-growth environmental conditions is critical to better understand the survival kinetics of foodborne pathogens in fresh-cut produce and to develop efficient interventions to mitigate the risk.

Comments

Copyright 2023 Avninder Kaur. All Rights Reserved.

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