Date of Graduation

5-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Cell & Molecular Biology (PhD)

Degree Level

Graduate

Department

Biological Sciences

Advisor/Mentor

Griffiths Atungulu

Committee Member

Burton Bluhm

Second Committee Member

Steve Ricke

Third Committee Member

Joshua Sakon

Fourth Committee Member

Jackson Lay

Keywords

Aflatoxin; Aspergillus; Fungi; Grain; Infrared; Microwave

Abstract

Electromagnetic-driven energy such as infrared (IR) technology holds great potential in deactivating Aspergillus flavus spores and prevents aflatoxin B1 (AFB1) contamination. Aflatoxins, highly toxic secondary metabolites primarily produced by Aspergillus species within the Flavi section (A. flavus, A. parasiticus, and A. nomius), pose substantial health risks to both humans and animals due to their significant toxicity and carcinogenic properties. Detecting and quantifying the presence and proliferation of these harmful fungi on food materials can be achieved by measuring the concentration of ergosterol. Ergosterol is a sterol compound produced in the cell membranes of fungi during their growth, providing a reliable indicator of fungal development. The objectives of this study were to 1) understand the growth and AFB1 production rate of Aspergillus flavus NRRL 3357, and 2) investigate the impact of different IR heat intensities on the growth and aflatoxin-producing potential of A. flavus. Thirty healthy corn kernels were inoculated with 1x106 spores/mL of A. flavus spores and incubated at 25oC. Then, A. flavus plate count, ergosterol, and AFB1 were measured every 24 h. In another experiment, inoculated corn incubated for 24 h was exposed to different IR heat intensities and heating durations. Afterward, the IR-exposed A. flavus were incubated for an additional 3 and 6 days (4 and 7 days of incubation in total), and the ergosterol and AFB1 concentrations were measured. For non-IR exposed A. flavus, the highest AFB1 concentration (32.2 µg/g) was observed after 6 days of incubation. Treatment at high IR heat intensities and heating duration resulted in low AFB1 and ergosterol concentrations. However, IR heat treatment at low intensities (e.g., 1.86 kW/m2) for 20 s resulted in high AFB1 and ergosterol concentrations (97.83 and 34.84 µg/g, respectively). Treatment of A. flavus NRRL 3357 with sub-lethal conditions (as identified in this study) resulted in an increase in growth and AFB1 production. This may be an indication that the sub-lethal treatment is causing a genetic mutation that is making the mold produce more AFB1 after exposure. The outcome of this study will strongly contribute to the advancement of electromagnetic-driven technologies’ design and/or optimization in a way to effectively kill pathogens on grain and prevent their regrowth and aflatoxin contamination.

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