USP <2021> Dietary Supplement Test for Bacteria Yeast and Mold

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What is the USP <2021> Test?

The USP <2021> method provides a snapshot in time of the bacteria and fungal content of a dietary supplement. It is the most common microbiological test conducted on dietary supplements and ingredients for dietary supplements. It is sometimes called a microbial limits test. It is often run at the same time as the USP <2022> test for pathogens in dietary supplements.

When is USP <2021> Required?

Dietary supplement manufacturers are required to “… [manufacture] under conditions and controls that protect against the potential for growth of microorganisms and the potential for contamination.” Manufacturers must also “…establish limits on…contamination that may adulterate…the dietary supplement.” In layman’s terms, USP <2021> is a microbial limits test, intended to measure whether or not a dietary supplement is within the microbiological specification set by the manufacturer.

What Microbes does USP <2021> Measure?

USP <2021> assesses total aerobic microbial count, which is total aerobic bacteria plus Enterobacterial count (Bile-Tolerant Gram-Negative Bacterial), and total yeast and mold. It is similar to USP <61>, the microbial limits test for personal care products.

The method is fully quantitative, so results are expressed as bacteria and fungi per milliliter or gram of product.

What is “Suitability” as Related to USP <2021

Per FDA, USP methods must be verified to be suitable for a specific product or ingredient before use in the testing of dietary supplements. Labs call these tests “suitability assays” and request their customers to conduct them once in the life of the product, before routine USP <2021> testing begins.

Summary of the USP <2021> method

The official standard method, as published by USP, offers some flexibility in testing. The summary below captures essential steps. If your company is considering a USP <2021> testing program with Microchem Laboratory, please contact us to discuss modifications that may be advisable depending on your specific dietary supplement products or ingredients.

A summary of the test method follows:

  • A suitability assays is first conducted for the dietary supplement or dietary supplement ingredient Note: Ingredients are tested separately from the final product by manufacturers to ensure the ingredients are also within microbial specifications.
  • All media is validated to have successful growth conditions before testing.
  • Sample is prepared at the desired concentration, typically 10 grams or ml into a much larger volume of nutritive media, then plated onto growth promoting media specific for the various classes of microbes under evaluation.
  • Plate(s) are incubated for different periods of time at different temperatures, depending on the class of microorganism being targeted.
  • Colonies growing on agar plates are counted, then dilutions are factored in mathematically to determine total aerobic microbial count, total combined molds and yeasts count, and enterobacterial count.

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USP <2021> Dietary Supplement Test for Bacteria Yeast and Mold

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