Recommendations for Designing and Conducting Cold-fill Hold Challenge Studies for Acidified Food Products

A scheduled process for an acidified food must be validated with existing data or a product-specific challenge study. We outline recommendations for designing, conducting and interpreting cold-fill-hold challenge studies for acidified foods and discuss information that should be included in reporting challenge study results to the U.S. Food and Drug Administration. Cold-fill challenge studies for acidified foods, designed and evaluated by expert food microbiologists, must take into account variability in ingredients, packaging, preservatives, and native microbiota. The studies should clearly document a 5-log pathogen reduction over four or more sampling times from at least two independent replicate trials, with pH measured at each sampling point. Inoculation is generally done in bulk and should account for no more than 1% of the product volume. The inoculum is most often a cocktail of at least three strains grown statically in broth containing 1% glucose to induce acid resistance. The pH challenged becomes the maximum pH for the scheduled process; the temperature becomes the lower limit for the hold time. Data analysis should consider the expected non-linearity of survival curves. These recommendations will help ensure that design, implementation, and interpretation of challenge studies for cold-fill-hold acidified foods meet scientific standards and adequately support product safety.