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Optimizing Formula Preservation
By: Eric S. Abrutyn, TPC2 Advisors Ltd.
Posted: February 26, 2010, from the March 2010 issue of Cosmetics & Toiletries.
page 3 of 7
Regulations and Preservative Testing
To protect the consumer, most governmental agencies have implemented regulations to address what constitutes a sterile, contaminant-free, pathogen-free product that is safe for consumer use. Some countries regulate the approved or unapproved types of preservatives allowed and control their maximum use levels. Besides governmental test recommendations, most preservative suppliers have internally tested their products and offer valuable and current data about them; this should be consulted before using a material in a finished product.
Product quality must be maintained throughout the normal use of the product by the consumer. To test the robustness of a formula’s preservation system to ensure it is sterile and safe for consumer use, the preservative level of a formula typically is tested 24–48 hr after processing (PET and D-Value pass/fail), after 1 month’s storage at 50°C (D-Value pass/fail), and after 3 months’ storage at 40°C (PET and D-Value). In addition, the following simple preservation tests can be used to assure that a consumer product is adequately preserved.
Preservation Efficacy Testing (PET): Also known as challenge testing, PET basically examines whether a product can withstand consumer contamination, and whether any contamination has occurred during manufacturing. If the sanitary quality of raw ingredients and processing equipment is maintained, there should be no initial contamination in the finished product. Unfortunately there are a number of possible protocols6 for this type of test, and each consumer company has its own in-house modifications based on specific needs.
The US Pharmacopeia (USP) and Personal Care Products Council also have published variations that are widely recognized as reliable methods. It should be noted that an aerobic plate count (APC) does not indicate how well a preservative is working because the preserved substance may not have been subjected to a significant bacterial load; i.e., the preservative system was not stressed. Thus, simply because no bacteria were present in the plates after an APC, this does not indicate the preservative system was efficacious.
D-Value: Determines the preservative efficacy as rate of kill. This method is good for selecting the type and concentration of a preservative to be used. It is also used as a measurement to indicate whether a formula is adequately preserved. Within this test, a linear regression method is used and the D-Value measurement indicates the number of hours required for a 90% reduction of the microbes introduced. The percentage of reduction is company-specific and may vary.
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