IAFNS presents new research on pathogens and low-moisture foods

New research on hazards in low-moisture foods fills critical knowledge gaps and identifies cutting-edge decontamination tools. The Institute for the Advancement of Food and Nutrition Sciences hopes the study will empower food safety professionals to reduce risks in the foods and prevent foodborne illness outbreaks.

Because the persistence of pathogens and viruses in ingredients and ready-to-eat foods has wide-ranging impacts on our food supply, the Institute for the Advancement of Food and Nutrition Sciences (IAFNS) is supporting a body of research on this topic. The studies focus on low-moisture foods such as nuts, dried fruits, cereal products and chocolate. These foods are often ingrediates in other foods, so they can potentially amplify outbreaks and recalls over a wide variety of products, according to researchers.

These studies were performed as part of a multi-center research collaboration between the University of Guelph, Health Canada and North Carolina State University. This collaboration enabled the investigators’ diverse perspectives and expertise to strengthen this line of research.

According to Jeff Farber of the University of Guelph, “the increased awareness of the importance of low-moisture foods (LMF) as a possible vehicle for foodborne illness has already led to better approaches toward prevention and control and will continue to do so in the future.”

The key findings from this series of studies and their impact on public health are summarized by IAFNS:

Identifying novel genes that facilitate survival of Salmonella in LMF
Ten genes important to Salmonella survival on LMF were impaired and their survival was studied on pistachios. Pistachios were treated with pathogens and then measured after treatment, after drying and after 120 days. The findings can be found here. 

Modeling Listeria monocytogenes survival on Model LMF
Three model LMFs were inoculated with a 4-strain cocktail of Listeria monocytogenes to evaluate their survival under long-term (8-12+ months) storage at 23 degrees C (73.4 degrees F) and 4 degrees C (39 degrees F). Decreases in Listeria monocytogenes during storage on the LMF were the result of both cellular inactivation and transition to a viable-but-not-nonculturable state. The surviving cells — specifically after long-term storage at 4°C on the chocolate liquor and pistachios — remained infectious and capable of replication. These findings will help predict future microbial health risk incidents. The paper also calls for adding LMF to food safety questionnaires used during listeriosis outbreaks because of this concern.

Pathogen inactivation
Two decontamination methods were studied for inactivating a cocktail of Salmonella or Listeria monocytogenes inoculated on dried strawberries, dried apples, raisins, chocolate crumbs, cornflakes and pistachios. One method was based on an acid-ethanol sanitizer and the other combined UV radiation, ozone and peroxide. Both methods show promise in reducing risks in LMF depending on the type of pathogen and product.

 Virus isolation
Foodborne viruses such as norovirus and hepatitis A virus are highly transmissible, persist in the environment, and resist inactivation. Foods can become contaminated with these viruses during harvest, handling or processing. This study compared a bead-based magnetic assay with an existing International Organization for Standardization method for virus recovery and tested it on chocolate, pistachios and cornflakes. Depending on the food matrix and the virus, the bead-based assay efficiently and rapidly extracts viruses from LMF.

Listeria monocytogenes survival and virulence on certain fruit
The survival of Listeria monocytogenes was measured during long-term storage on three fruits. After dry inoculation and storage at two different temperatures and humidity levels, the results show that Listeria monocytogenes is rapidly inactivated during storage on raisins and dried strawberries at 23 degrees C, but capable of long-term survival at 4 degrees C.

Virus inactivation
This study examined the survival of foodborne viruses in LMF during four-week storage at room temperature. It also evaluates a treatment geared toward inactivating viruses. Pistachios, chocolate and cereal were inoculated with hepatitis A virus and two related viruses. Then viral survival was measured over a four-week incubation at room temperature. The study found that while foodborne viruses can persist for a long time in LMF, combining UV radiation, ozone and peroxide as a treatment may represent an effective inactivation method.

Viable but nonculturable
In this study, dried apples, strawberries and raisins were mixed with a five-strain cocktail of Salmonella and then dried. However, Salmonella could not be recovered, even after being enriched. The use of microscopy methods revealed that 56 percent to 85 percent of Salmonella cells were still viable despite their nonculturable state. These data suggest that the unique combination of stressors on dried fruit can keep pathogens viable but undetectable by culture, posing hidden risks for food safety.

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