The ISO 11930 - Preservative Challenge Test is a procedure for evaluating the antimicrobial protection of a product. Much like the USP <51>, it evaluates the activity of preservatives or other intrinsic characteristics of a product that help maintain the safety of a product by inhibiting the growth and reducing the amount of microbial contaminants. Unlike the USP <51>, the ISO 11930 method is written specifically for cosmetic products. It is quickly becoming the "go to" test method for evaluating the preservative effectiveness of cosmetics and personal care products. It is intended for water soluble cosmetic products, but can be adapted for products where water is the internal phase.

The ISO 11930 preservative efficacy test method is based on the inoculation of a personal care product with a known concentration of 5 relevant strains of microorganisms, specifically S. aureus, E. coli, P. aeruginosa, C. albicans, and A. brasiliensis. The remaining concentration of microorganisms is determined at defined intervals during a period of 28 days. For each time and each microorganism, the log reduction or percent reduction is calculated and compared to the acceptance criteria required by the method for acceptable preservation.

Summary of ISO 11930 Test Procedure

  • Prior to the test, the microbiological quality of the product should be determined by USP <61>, Aerobic Plate Counts, or other similar methods.
  • The product is separated out into 5 containers, each being challenged with one of the 5 method-specified microorganisms at a concentration of >1x105 CFU/g or ml.
  • The initial concentration of each microorganism is determined by standard dilution and plating techniques.
  • At the time of test initiation, a separate aliquot of the product, typically 1 g or 1 ml, is placed in a volume of neutralization broth to be used in the neutralization and recovery validation.
  • The product is held at room temperature for a period of no less than 28 days.
  • The inoculated product is evaluated at 7, 14 and 28 days after inoculation and surviving microorganims are enumerated using standard dilution and plating techniques.
  • Test sample colonies are counted at each specified interval to determine the amount of microorganisms remaining.
  • The log reduction of each microorganism at each interval is calculated and reported.
  • The effectiveness of the preservative system is determined by comparison to the acceptance criteria.

ISO 11930 Acceptance Criteria

  • Criteria A:
    • For bacteria, the product must demonstrate no less than a 3 log reduction from the initial count at 7 days, and no increase from the 7 day count at days 14 and 28.  
    • C. albicans must be reduced by no less than 1 log at 7 days and show no increase from the 7 day count at days 14 and 28.
    • A. brasiliensis must show no increase from the initial count at 14 days and no less than a 1 log reduction at 28 days.
  • Criteria B:
    • For bacteria, the product must demonstrate no less than a 3 log reduction from the initial count at 14 days and no increase from the 14 day count at day 28.
    • C. albicans must be reduced by no less than 1 log at day 14 and show no increase from the 14 day count at day 28.
    • A. brasiliensis must show no increase from the initial count at 14 and 28 days.

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