The control of Salmonella in low moisture foods is the key to safe low moisture food products.  The Food Safety Modernization Act (FSMA) mandates that food producers have science-based preventive controls to mitigate the risk of foodborne illness.  In other product commodities, validation studies for traditional thermal processing may be well established, such as in low-acid canned foods.  Additionally, the National Advisory Committee of Microbiological Criteria for Foods developed guidelines for conducting challenge studies in a variety of foods.  Unfortunately, unique attributes of low moisture foods pose additional challenges that are not included in these guidelines.

When preparing to perform a validation study, proper forethought is required, especially in the case of low moisture foods.  Some of the first decisions include:

  • Choice of appropriate microorganism(s)
    • Choice of the pathogen(s) of interest – In choosing the appropriate pathogen, one needs to consider the occurrence in the environment, association with product commodities, association with outbreaks/recalls, infections dose, severity of illness, and resistance to the inactivation process. The choice of the appropriate or pertinent pathogen may not be the same organism that would be selected for a high moisture product. An example is Salmonella Senftenberg 775W which is extremely heat-resistant in high moisture products, but has been found to be less resistant than other Salmonella serovars at low moisture.
    • Choice of an appropriate surrogate microorganism (as required) – When working in the plant setting, it is imperative to not introduce pathogenic microorganisms during validation testing. When selecting a surrogate microorganism, it is important to consider the appropriateness of the surrogate for the product, process, and pathogen of interest; as well as ensure that the surrogate microorganism does not take up residence within the equipment or processing facility.
  • Inocula preparation – Research has shown that pathogens grown on the surface of media (sessile environments) are more stable in low moisture foods than those grown in broth (planktonic environments). It is also important to consider appropriate harvesting techniques.
  • Inoculation into food – When working with low moisture foods, it is important to consider how ingredients become contaminated, and attempt to mimic natural contamination in a laboratory setting. It is critical to retain the original characteristics of foods by adding as little moisture as possible during inoculation. The inoculated food or ingredient should have a homogeneous, stable, and known high concentration of cells prior to inactivation testing.
  • Re-equilibration of foods post-inoculation – Following inoculation, a limited re-equilibration period may be essential to allow the product characteristics and inoculum to stabilize. It is important to understand the appropriate minimum and maximum lengths of storage that are suitable for various foods, pathogens, and timelines associated with the validation study.

More information on preparing for and conducting a low moisture validation study can be found through the Low Moisture Foods Safety Task Force, Low Moisture Food Pasteurization Alliance, Almond Board of California, PMMI and OpX Leadership Network, as well as other resources online.  For individuals interested in learning more about Validating Pasteurization Processes for Low Moisture Products, a workshop is being offered in conjunction with the International Association for Food Protection’s 2017 Annual Meeting.