Article Summary: Gluten-Free Labeling: Are Growth Media Containing Wheat, Barley, and Rye Falling through the Cracks?

Article Summary: Gluten-Free Labeling: Are Growth Media Containing Wheat, Barley, and Rye Falling through the Cracks?

Article Summary:

Gluten-Free Labeling: Are Growth Media Containing Wheat, Barley, and Rye Falling through the Cracks?

Tricia Thompson, Melinda Dennis, Luke Emerson. J Acad Nutr Dietet. 2017. In Press. 

Background: Bacteria are used in a variety of products, including probiotics. These microorganisms may be grown on media that may include ingredients derived from gluten-containing grain (ie, wheat, barley, and rye). Historically, some concern has been expressed in the celiac disease community that the use of gluten-derived/ gluten-containing growth media may result in residual gluten protein fragments remaining in products containing microorganisms such as bacteria. One obstacle preventing the resolution of whether residual gluten sometimes remains in products containing bacteria is the general lack of readily available information on the growth media used to cultivate these microorganisms. Further study of fermentation media used to produce bacteria is needed to determine whether allergenic or gluten protein remain. This suggestion is based on real-world test results of a commercially available probiotic containing a bacterial strain with known growth media: one formulation gluten free and the other not.

What we tested: Gluten Free Watchdog, LLC, a gluten test reporting service in Manchester, MA, tested a popular probiotic through Bia Diagnostics, LLC on three separate occasions. While the bacterial strain remained the same in all lots, the growth media was different—spent brewer’s yeast or molasses. The probiotic was tested using the R5 ELISA Ridascreen Gliadin Competitive R7021 (R-Biopharm AG). A competitive ELISA is used when assessing food for gluten protein fragments, which occur when gluten protein is hydrolyzed or fermented. Bacteria (and the enzymes they produce) in the probiotic were deactivated before testing to prevent false-positive results. The probiotic containing the bacterial strain grown on spent brewer’s yeast (and likely contaminated with barley malt) tested at > 283.5 ppm gluten. The same probiotic containing the same bacterial strain but this time grown on molasses tested at < 10 ppm gluten on two separate occasions.

What we need in the future: In the United States, the FDA should clarify for industry whether growth media for bacteria (and other microorganisms) are considered ingredients, incidental additives, or processing aids, and whether the use of wheat, barley, or rye precludes the food containing the bacteria from being labeled as gluten free. If the use of gluten-containing growth media does not preclude a gluten-free labeling claim, then the FDA should clarify how products containing bacteria should be tested to ensure safety for gluten-free consumers.

Recommendations: In the meantime, individuals with gluten-related disorders should be encouraged to use only those probiotics labeled as gluten free. Manufacturers labeling probiotics gluten-free should be encouraged to test their products using the competitive R5 ELISA, especially if bacterial strains included in the product are grown in gluten-containing growth media.

Questions? Please contact Tricia Thompson at

This article is available free of charge to members of the Academy of Nutrition and Dietetics


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Comments (5)

  • Sharon Habiger Reply


    Do you think this may apply to Kombucha drinks?

    January 23, 2018 at 6:43 pm
    • Tricia Thompson Reply

      I don’t know. It depends on the growth media. Do you have some product links you can send me?

      January 23, 2018 at 8:57 pm
  • Jean Reply

    Tricia –
    Thank you for sharing this information. Reminds me of previous discussions about wheat being used in growing mushrooms and strawberries. Have there been tests on the gluten content of mushrooms?

    October 26, 2018 at 1:19 pm

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