Persistence and Survival of Pathogens in Dry Foods and Dry Food Processing Environments

ILSI Europe Report Series. 2011:1-48

Low-moisture foods and food ingredients, i.e., those appearing to be dry or that have been subjected to a drying process, represent important nutritional constituents of human diets. Some of these foods are naturally low in moisture, such as cereals, honey and nuts, whereas others are produced from high-moisture foods that were deliberately submitted to drying (e.g., egg and milk powders). The addition of large amounts of salt or sugar can also be regarded as a ‘drying’ process by reducing the amount of water available for microbial growth. Some foodborne pathogens can survive for long periods in low-moisture foods and environments, and in some cases at doses that can cause infections. Many microorganisms can resist drying processes, especially after exposure to nonlethal stress conditions, including sub-lethal heat treatment or acidic environments.

If dry foods are reconstituted (rehydrated) before consumption, there is a possibility that bacterial pathogens will grow if products are subsequently stored under inappropriate conditions, potentially resulting in populations sufficient to cause infection or intoxication. Food plants, in which low-moisture foods are produced, are difficult to clean and sanitise effectively, and there are instances of persistence of specific strains of pathogens for extended periods of time.

Because microorganisms may survive during drying processes or persist in low-moisture foods and dry food processing environments, it is imperative that Good Hygiene Practices (GHPs), GMPs and HACCP systems, with specific attention to preventing survival and persistence of foodborne pathogens, be implemented and effectively maintained on a continuous basis. The ILSI Europe report examines the extent to which the industry uses monitoring programmes to aid in their understanding of the bacterial ecology and niches. The report attempts to identify how this understanding is translated to enhance the microbiological safety of the process, identify where there are gaps/failures in this system and how to remedy them. This report summarises information on the survival of foodborne pathogens in low-moisture foods (aw < 0.85) and in dry food processing environments. Pathogens that have been known to cause outbreaks of infections or intoxications associated with consumption of low-moisture foods, as well as those not yet implicated in outbreaks, are discussed.

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