Author ORCID Identifier

https://orcid.org/0009-0007-4237-6777

Semester

Spring

Date of Graduation

2025

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Animal and Nutritional Sciences

Committee Chair

Jacek Jaczynski

Committee Co-Chair

Kristen Matak

Committee Member

Kristen Matak

Committee Member

Cangliang Shen

Committee Member

Jianbo Yao

Committee Member

Ibukun Ogunade

Abstract

Yellow mealworm (Tenebrio molitor) larvae have gained attention as a sustainable and nutritionally balanced food source, yet their high natural bacterial load raises food safety concerns. This study investigates the impact of pre-processing, processing, and storage conditions on microbial load and diversity in mealworms, comparing thermal (hot) and non-thermal (cold) treatments. These treatments include freeze-drying, wet heat treatments, dry heat treatments, and the combination of wet and dry heat treatments against untreated controls. Microbial loads were quantified by plate counts after day 0, day 10, and day 28 of vacuum-sealed refrigerated (4°C) storage. Water activity (Aw), pH, and moisture content were also analyzed to assess variability of intrinsic properties. Significant log reductions occurred under thermal treatments (4.59 ± 0.35 Log CFU/g for hot treatments vs. 8.15 ± 0.43 Log CFU/g for cold treatments). While no significant microbial growth occurred by day 10 (p > 0.05), a notable increase was observed by day 28 (p = 0.006), particularly in heated samples (p < 0.05). Anaerobic and psychrotrophic bacteria followed similar trends, whereas yeast and mold counts remained low and consistent throughout storage. These findings highlight the effectiveness of heat processing in mitigating microbial risks, supporting safer mealworm integration into food systems. Additionally, this study examines batch-to-batch microbial variability in fresh, uncleaned and unprocessed T. molitor larvae from three seasonal batches and comparing results with literature values. Aerobic, anaerobic, psychrotrophic, and yeast/mold counts were assessed, revealing significant seasonal variations—with the September batch exhibiting the highest microbial loads (p< 0.05). While aerobic and yeast/mold counts aligned with prior studies, anaerobic and psychrotrophic counts diverged, likely due to geographic and methodological differences. These variations underscore the influence of seasonal factors, rearing practices, and processing on microbial profiles, emphasizing the need for standardized monitoring in edible insect production. Together, these findings provide critical insights into microbial safety and variability in mealworms, informing strategies for their safe adoption as a sustainable food source.

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