Study of Listeria Sampling Practices Aims to Improve Frozen Food Safety
Large food producers are testing for Listeria monocytogenes in their frozen food manufacturing facilities, at least to some degree, according to a new study from the University of Georgia in Athens. Researchers used an anonymous survey to collect information from more 46 frozen food production facilities to better understand existing environmental monitoring.
Although frozen foods do not support the growth of L. monocytogenes, the moist and cold conditions in frozen food production environments are favorable for its growth. The purpose of the study was to determine the current state of awareness and practices applied across a variety of frozen food facilities related to environmental monitoring for Listeria.
The survey indicated that facilities are more likely to test for Listeria spp. in environmental monitoring zones 2 to 4 (nonfood contact areas) on a weekly basis. The major areas of concern in facilities for finding Listeria-positive results are floors, walls, and drains. The survey showed that few facilities incorporated active raw material and finished product testing for Listeria; instead, programs emphasized the need to identify presence of Listeria in the processing environment and mitigate potential for product contamination.
The researchers concluded that recognition of environmental monitoring as a key component of a comprehensive food safety plan was evident among the facilities surveyed, along with an industry focus to further improve and develop verification programs to reduce prevalence of L. monocytogenes in frozen food processing environments.
“Over the last few years, the FDA has started putting more emphasis on Listeria monocytogenes,” says Mark Harrison, PhD, lead author of the study and a professor in the university’s department of food science and technology, referring to the revised environmental monitoring guidelines to industry for ready-to-eat foods issued by the FDA in 2017.
While there are at least half a dozen species of Listeria, only L. monocytogenes is dangerous to humans, he says. Listeria is prevalent in nature and in production facilities, some of which test for multiple types of Listeria and some only for L. monocytogenes. An estimated 1,600 people in the U.S. each year develop listeriosis, a serious infection typically caused by eating food contaminated with the Listeria monocytogenes bacterium, and approximately 260 people die, according to the CDC. The infection is most likely to sicken pregnant women and their newborns, adults aged 65 or older, and people with weakened immune systems.
Dr. Harrison adds that frozen food producers need to review their sampling strategy for L. monocytogenes, including the frequency and timing of sampling. Although there are no guidelines with precise recommendations for sampling, he says regular testing can identify problem areas. “Facilities should focus on looking for Listeria monocytogenes at times and in places where they are most likely to find the pathogen for a realistic assessment,” he adds.
Listeria monocytogenes is ubiquitous in the environment and can be brought into facilities on clothing and shoes, he says. It also can survive freezing temperatures. Floors and walls tend to be places where the pathogen is frequently found. The study found that facilities generally tested non-contact areas weekly.
“This survey demonstrates there is a pretty high awareness in the industry of the risks of Listeria monocytogenes,” says Sanjay Gummalla, PhD, senior vice president of scientific affairs at the American Frozen Food Institute in Arlington, Va. The institute funded the University of Georgia study and several other related studies.
Dr. Harrison is working on another study funded by the institute that relies more heavily on data to help answer questions about whether to sample a certain area of a production facility, and how often. we got a snapshot of the industry now,” he says. “We found it is aware of Listeria and the need for additional training and resources.”