Food Science and Technology Department

 

First Advisor

Andréia Bianchini

Second Advisor

Jayne Stratton

Committee Members

Devin Rose

Date of this Version

8-2024

Document Type

Thesis

Citation

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 Professor Andréia Bianchini

Lincoln, Nebraska, August 2024

Comments

Copyright 2024, Aryany Leticia Peña-Gomez. Used by permission

Abstract

Wheat-based products, traditionally considered low-risk due to their low moisture content, have been involved in numerous foodborne outbreaks in recent decades. Salmonella and Shiga toxin-producing Escherichia coli (STEC) present in these products have caused significant numbers of hospitalizations and massive product recalls. The microbiological quality of flour is highly dependent on the incoming wheat, which is vulnerable to contamination from field to milling. Once pathogens are present in flour, they can survive for extended periods. Implementing strategies to mitigate the risk of pathogen contamination throughout the wheat processing chain is critical.

This study evaluated the distribution of E. coli present in intentionally contaminated wheat into milling fractions and equipment, and the efficacy of mitigating interventions during wheat milling. Non-flour milling fractions exhibited the highest E. coli contamination, also reflected in the equipment surfaces. Additionally, significant contamination levels were observed in straight-grade flour. The processing of non-contaminated wheat and the implementation of a cleaning intervention led to the reduction of E. coli below the limit of detection in most flour fractions and equipment surfaces. This study highlights that microbial contamination in wheat milling can easily occur. Moreover, it demonstrates that microbial contamination can be flushed through the system by processing wheat with superior microbial quality and by implementing simple cleaning interventions.

This study also investigated the survivability of Shiga toxin-producing E. coli (STEC) O121 in wheat flour, buckwheat flour, and cake mix at varying water activity levels during storage. STEC O121 remained quantifiable throughout the duration of the study (112 days), with no significant impact of the water activity levels on survival. Differences were observed among the evaluated products, with the highest STEC reduction in cake mix, followed by wheat flour and buckwheat flour. Different STEC inactivation parameters were found among the products. These findings demonstrate the survivability of STEC O121 in low water activity foods and the role of the food matrix on the tolerance of these pathogens to low moisture environments.

Advisor: Andréia Bianchini

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