Author ORCID Identifier

https://orcid.org/0000-0001-5163-3690

Semester

Spring

Date of Graduation

2023

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Human Nutrition and Foods

Committee Chair

Cangliang Shen

Committee Co-Chair

Nettie Freshour

Committee Member

Jacek Jaczynski

Abstract

This study aimed to evaluate and model the survival of Listeria monocytogenes on organic HoneyCrisp (HC) and Fuji (FJ) apples during storage at various temperatures. Fresh organic HC and FJ apples (without wax coating) obtained from a local wholesale market were inoculated with a 2-strain mix of L. monocytogenes followed by storage at 5.0 (22.9% RH), 12.0 (37.0% RH), and 22.5oC (50.4% RH) for 60, 35, 7 days, respectively, and periodically (day-0 to 60) analyzing microbial populations. Surviving L. monocytogenes were spread-plated on Modified-Oxford agar after 10 or 100-fold serial dilution. Data were analyzed using the mixed-model procedure of SAS and GinaFit software. The initial populations of L. monocytogenes on HC and FJ apples ranged from 6.23-6.89 log10CFU/apple for storage at 5, 12, and 22.5°C. The pathogen survival cell counts decreased (P < 0.05) to 2.34-4.05, 2.72 -2.98, and 2.47-3.75 log10CFU/apple by the end of the storage at 5, 12, and 22.5°C, respectively. L. monocytogenes was more sensitive (P < 0.05) on FJ than HC apples and at room temperature than refrigerated temperatures. The inactivation parameters calculated from the Linear, Weibull, and Biphasic models are generally consistent with the pathogen survival curves with few exceptions. The results of this study filled the data gap for understanding microbiological risks associated with post-harvest practices of tree fruit production. Future studies are needed to quantify the natural wax amount on various organic apples and develop pre- and post-harvest intervention strategies for the inactivation of foodborne pathogens on apples and other tree fruits.

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