Author ORCID Identifier

https://orcid.org/0009-0001-3868-5637

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

Cangliang Shen

Committee Member

Cangliang Shen

Committee Member

Kristen Matak

Abstract

Edible insects are emerging as sustainable and nutritious alternatives to conventional protein sources. However, concerns about food safety, particularly the presence of pathogenic bacteria such as Escherichia coli and Listeria monocytogenes, remain a barrier to consumer acceptance and industrial use. This study evaluated the effectiveness of thermal processing in inactivating E. coli, L. monocytogenes, and their non-pathogenic surrogates (E. coli JM109 and Listeria innocua) in both fresh and dehydrated forms of Tenebrio molitor (mealworm) and Acheta domesticus (cricket). It also evaluated the influence of insect species, moisture content, and temperature on microbial inactivation. A microbial challenge study was conducted by inoculating fresh mealworms and crickets with the target bacteria to levels above 9 log CFU/g. Dehydrated samples were produced via oven and freeze-drying. Inoculated samples were vacuum-sealed in thin pouches (< 1 mm) and subjected to thermal treatment at 60–90°C for up to 5 minutes using a circulating water bath. Survivors were enumerated via standard 10-fold serial dilution and spread plating. D- and z-values were calculated to determine inactivation kinetics. Data were analyzed using a generalized linear mixed model (GLIMMIX) with a Negative Binomial distribution. Thermal resistance, indicated by D-values, was significantly influenced by bacterial strain and temperature (p < 0.0001) and by treatment type (p = 0.0075) but not by insect species (p = 0.5065). D-values varied depending on processing, with fresh samples having significantly higher values than dehydrated ones (p = 0.0020), and both treatments having lower values than desiccated bacteria, which had the highest D-value (p < 0.0001); however, no significant difference was observed between freeze-dried and oven-dried samples (p = 0.4886). Across insect types, the non-pathogenic E. coli JM109 exhibited the highest D70, 144 seconds, indicating increased thermal resistance, while E. coli O157:H7, L. monocytogenes, and L. innocua had lower D-values (D70) of 36, 29, and 31 seconds, respectively, for mealworm samples in the fresh treatment group. L. innocua showed comparable thermal resistance to L. monocytogenes, supporting its use as a suitable non-pathogenic surrogate. In contrast, the high D- and z-values observed for E. coli JM109 suggest that it may overestimate pathogen resistance under real-world conditions. Intrinsic properties of insects such as water activity, moisture content, and pH results were used to understand their effects on microbial inactivation kinetics. This study provides critical insights into the thermal inactivation kinetics of key foodborne pathogens and their surrogates in edible insects. While L. innocua is validated as a suitable surrogate for L. monocytogenes, the elevated resistance of E. coli JM109 highlights its limitations in simulating E. coli O157:H7. The findings support the development of safe thermal processing strategies for edible insects, contributing to food safety assurance in this emerging protein source. Additionally, the reduction in water activity, pH, and moisture content due to dehydration plays a significant role in influencing thermal resistance.

Download

Share

COinS