Best Practices for Pathogen Detection in Low Moisture Foods

Beyond Finished Foods: Production Environments

In contrast to the historical focus on testing finished products for pathogens just prior to release with little or no attention given to the processing operation and environment, new guidelines and regulations place more attention on environmental monitoring and entire process operation as means to prevent pathogen contamination.

The FSMA Preventive Controls rule, for example, focuses both on environmental monitoring and finished product testing for human food. In addition to recommending that raw materials, ingredients, and end products be tested, FSMA highly recommends environmental monitoring of pathogens in LMF and ready-to-eat (RTE) food processing environments. According to FSMA, “Foods such as peanut butter, soft cheeses, dried dairy products for use in RTE foods, and roasted nuts are among the products for which manufacturing operations would need to have an environmental monitoring program when such foods are exposed to the environment.”

In addition, when environmental monitoring results are gathered both prior to and following cleaning, manufacturers gain a good sense of the overall effectiveness of their hygiene controls and sanitation program. Armed with strong before and after data, they can make the necessary adjustments to improve cleaning strategies, practices, and training.

Carefully designed and implemented sampling programs also bring the benefit of detecting sites potentially harboring pathogens. To that end, LMF manufacturers are advised to perform environmental swabbing and analysis using a hygienic zoning system based on food safety risk. An example would be Zones 1 through 4, with Zone 1 being product contact surfaces, Zone 2 being surfaces immediately over or next to the product, then moving to Zones 3 and 4, with Zone 4 being furthest from the product.

Pathogen Control in LMFs

Every step of the LMF production chain—from sourcing of raw commodities and ingredients, preventing cross-contamination from harvest, to post-process, employing effective dry cleaning and sanitation processes, and implementing and monitoring validated lethal processes—is critical to ensure safer LMFs. Although today’s thermal (heat) processes coupled with continuous monitoring are probably adequate, there is significant room for improvement.

Thermal processes for nuts include oil roasting, dry roasting, and blanching as more traditional practices, but heat can also be applied through steam, infrared heat, and other means. Pasteurization has been successfully applied to raw almonds to reduce the presence of Salmonella. Some emerging technologies for LMFs include radio frequency and microwave heating, nonthermal plasma, pulsed light, UV light, irradiation, propylene oxide, ozone, and novel drying technologies such as microwave drying, vacuum drying, super-heated steam drying, infrared drying, and freeze drying. Although high-pressure processing has been successfully applied to high moisture foods, efficacy in LMFs is not well understood. Additional research is needed to understand these technologies’ application to LMFs.

Pathogen Detection Technologies and LMFs

Eliminating or preventing pathogens entering the production process through raw material screening and finished product testing are key to ensuring safe product is delivered. Unfortunately, processes that rely on inadequate or incorrectly used technologies can thwart a lot of well-meaning work.

High-performing pathogen testing technologies are able to identify intact pathogens, as well as pathogen cells that may have been damaged by freezing, drying, antimicrobial treatments, or other processing conditions. Pathogen detection methods typically require an enrichment step to allow bacteria to grow to detectable levels, and this nourishment and recovery step is especially critical for LMFs. Pathogens in these foods can be severely dehydrated due to the low water activity, and recovery and detection of desiccated bacteria from dry matrices and environments is critical.

Manufacturers of food—LMFs or otherwise—mostly utilize one of two test tools for detecting the bacteria in their low moisture products: culture-based tests and rapid methods. Traditional culture-based tests rely upon growth of pathogens in a selective media followed by counting of visible colonies based on certain traits, such as their ability to grow in the presence of a particular chemical (e.g., salts, bile) or their ability to utilize particular chemicals or nutrients. Rapid methods for foodborne pathogen detection have evolved over the last several years with fundamental advances in immunology and molecular biology and applications of these advances to testing methods. The accuracy of these rapid methods is generally validated against the same standard methods used in culture methods—FDA BAM, ISO, or USDA MLG, for example. However, compared to traditional culture tests, these rapid methods not only offer enhanced accuracy but drastically reduce the time-to-result of food testing (next day findings rather than three days to a week) and provide greater ease of use.