It seems the pear industry is doing well when it comes to food safety on pear harvest, packing and storage. This is according to a study partially funded by the Center for Produce Safety (CPS).
During a Sept. 10 CPS webinar, Laura Strawn — professor and extension specialist at Virginia Tech — presented findings from a recently completed study into food safety risk mitigation in pears. The study used a metagenomic approach to catalog microbiological communities present on pears at harvest, during various stages and conditions of storage, and at retail.
Among other things, the study found that the packing line reduced microbial load — including of foodborne illness-causing microbes — on pear surfaces, and that method and length of storage changed the volume and makeup of microbial communities on pears.
“We were able to find that Listeria monocytogenes and generic E coli did not grow on intact pears throughout the entirety of storage,” says Strawn, the study’s principal investigator, adding that “wrapping of the pears significantly reduced Listeria monocytogenes levels.”
Objectives, Purpose and Findings
The study had three main objectives:
- Identify what kinds of microbial communities are present on whole, intact pears prior to storage. D’Anjou pears were used in the study.
- Identify and quantify what microbial communities are present on marketable (whole, intact) and unmarketable (mechanically damaged) pears in bulk bins and individually wrapped in storage for three, six and nine months under industry-standard environments, and track the changes over those storage times.
- Track what happens to listeria colonies across storage conditions and lengths when applied to pears individually and in combination with other microbes that could be found on pears
“We really wanted to characterize the microbiota of these pears under different storage practices and provide evidence-based recommendations for both food safety and then also a little bit of quality management if possible,” Strawn says of the motivation behind the study. She adds that other tree fruit, especially apples, have benefited from similar investigations.
“But we really didn’t have those strong science-backed recommendations for our pear industry, and this was a really wonderful opportunity to do it,” she says.
On the first objective, the study found that the types of microbes on pears — the microbial communities — at harvest and after running through the packing line didn’t change much. But the number of microbes decreased significantly after passing through the packing line, “confirming the value of postharvest handling,” the report reads.
Strawn also notes that listeria was not found natively on pears in the study. Though another part of the study involved inoculating pears with listeria to see what happened under different conditions, they did not find the microbe on uninoculated pears.
On the second objective, the study made the surprising finding that the microbial communities were very similar between intact marketable pears and mechanically damaged unmarketable pears. However, wrapping pears in antimicrobial wrapping had a noticeable impact, both reducing the number of microbes present and decreasing the variety of microbes.
Finally, on objective three, the study found that listeria just didn’t grow on pears across storage. Large volumes of listeria and other co-inoculate microbes were applied to the study’s pears, and while listeria was still observable on the pears by seven months of storage, there was never any growth. Instead, volumes declined from inoculation levels under all tested conditions.
Impact for Industry
While all the findings were valuable to the pear industry, Strawn characterizes the finding that listeria didn’t grow on pears through storage as especially important.
She says it means the pear industry needs to “stay focused and vigilant on our food safety programs to prevent that initial contamination because we were able to show that if you have no contamination, it’s not going to be a supportive environment.”
She points to the large-scale outbreaks of listeria from produce, noting that such outbreaks stem from high levels of initial contamination followed by microbial growth, or “amplification.”
“So, being able to show that your commodity, under your operation and whatnot, doesn’t grow or ever show that amplification — it’s really important,” she says. “Because then you can say, ‘OK, good, we’re not getting any amplification. Now let’s really focus in on our good agricultural practice programs or good manufacturing practices. All the things we do around sanitation and worker health and hygiene, all that stuff and make sure that we’re not getting any kind of potential contamination.’”
Strawn also points to the findings that wrapped pears in storage showed less varied and reduced microbial loads compared to bulk-stored pears as useful to industry. She acknowledges that wrapping pears is labor-intensive and comes with a big cost, so moving the industry to wrapping is not desirable. But she adds that it could be a quality-preserving strategy “if you did have a lot come in that you were particularly concerned about or you thought might be more prone to disease.”
