A recently completed study funded by the Center for Produce Safety (CPS) has provided new insights into Listeria monocytogenes growth, survival, and inactivation on pears during packing and in storage. The study also established a foundational dataset describing microbial communities on pears before and during storage, enabling future food safety risk assessments and intervention development.

The study, led by Laura Strawn, Ph.D. of Virginia Tech University, looked at changes that occur in microbial communities on whole green Anjou pears, beginning in the orchard before harvest through nine months of controlled atmosphere (CA) storage, with a focus on how key microbial players may affect food safety risks during storage. The researchers also investigated how L. monocytogenes populations behave on pears in refrigerated and CA storage.

Anjou pears were selected for the study due to their long shelf life.

Dr. Strawn’s team first identified culturable microbes (i.e., yeasts, molds, and lactic acid bacteria) on whole pears before storage. Next, the scientists sampled microbial communities on marketable and unmarketable pears, both in bulk and wrapped, during long-term CA storage at three, six, and nine months. Using metagenomics, they created a profile to track microbial population shifts over time.

To study L. monocytogenes behavior, the researchers co-inoculated the pathogen under industry-relevant conditions with common spoilage mold species and other microorganisms found on pears.

The results showed no growth of L. monocytogenes on whole, intact pears under any tested condition. However, L. monocytogenes that were present remained intact for up to seven months during controlled atmosphere storage—underlining the importance of addressing pathogen persistence, not just growth.

Antimicrobial wrapping was seen to significantly reduce L. monocytogenes levels—by more than 5 log colony forming units (CFU)—and inhibited the growth of plant pathogen Penicillium expansum, demonstrating its potential as a practical, dual-purpose intervention for food safety and quality.

Interestingly, when pears were co-inoculated with P. expansum, the levels of L. monocytogenes declined more rapidly. In contrast, Aureobasidium pullulans and Bacillus thuringiensis (potential biological control organisms) had little to no impact on L. monocytogenes survival.

The researchers also found that pears sampled after passing through the packing line showed significantly reduced total microbial load, confirming the value of postharvest processing.

During storage, bacteria and fungi became more dominant over time. Pears stored in antimicrobial wrap showed lower microbial richness and diversity, compared to those stored in bulk.

Co-Principal investigators on the study included Faith Critzer, Ph.D. and Hendrik den Bakker, Ph.D. from the University of Georgia’s Center for Food Safety; and Alexis M. Hamilton, Ph.D. of Virginia Tech.