U.S – Two groundbreaking studies, funded by the Center for Produce Safety (CPS), are harnessing the power of genomic sequencing to delve into the impact of storage conditions on microbial growth, particularly focusing on the presence of Listeria monocytogenes on pears.

Both studies employ metagenomics techniques, involving the sampling of microorganisms residing on pear skin, analyzing their DNA, and identifying them using computer software.

This advanced approach provides a more comprehensive understanding of microbial communities compared to traditional culturing methods, which can be biased by specific techniques.

Study 1: Dynamics of microbial communities on whole green anjou pears

Led by Dr. Laura Strawn of Virginia Tech University, the first study tracks changes in microbial communities on whole green Anjou pears, starting from the orchard before harvest through nine months of controlled atmosphere (CA) storage.

The focus is on understanding how key microbial players influence food safety risks during storage, with specific attention to L. monocytogenes populations in refrigerated and CA storage.

Using metagenomics, Dr. Strawn’s team identified culturable microbes on pears before storage and tracked microbial population shifts over time during long-term CA storage.

Preliminary results indicate that pears may not be a hospitable environment for L. monocytogenes. Additionally, the study provides insights into the succession of decay-causing microbes, aiding in identifying postharvest storage practices influencing microbial populations and deciphering drivers behind pear spoilage.

Study 2: Microbial population dynamics on pear surfaces

Conducted by Dr. Meijun Zhu of Washington State University, the second study investigates potential shifts in microbial populations on pear surfaces during long-term CA and cold storage. The research aims to fill crucial data gaps on L. monocytogenes die-off dynamics, informing industry food safety plans.

Dr. Zhu’s research involves three pear varieties—Bartlett, D’Anjou, and Bosc—representing both summer and winter varieties with different skin characteristics. The study includes conventionally grown and organically produced pears, considering the impact of organic production practices on microbial populations.

Inoculating unwaxed pears with a non-pathogenic strain of L. monocytogenes, the researchers measured die-off and potential shifts in microbial populations during commercial CA and cold storage over a nine-month period.

Preliminary results indicate a rapid decrease and eventual stabilization of L. monocytogenes populations.

Both studies contribute significantly to understanding the dynamics of microbial communities on pears and the behavior of L. monocytogenes under various storage conditions. The metagenomic analyses being conducted hold promise for identifying potential biological control agents based on microbial interactions, offering innovative solutions for enhancing food safety in the produce industry.

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