Gluten Testing: Current Detection Methods—And Their Limits

Like all sampling issues, you can mitigate the problem by taking multiple samples or, sometimes, by the effective use of composite samples.

Detecting gluten in used frying oil is more challenging. “To do gluten analysis on used frying oil, you must first try to extract the gluten with ethanol/water solvent, but you probably won’t get all of the gluten into the extract so you will underestimate the gluten level in oil,” says Dr. Taylor. Since consumers never eat oil except for the amount absorbed in the food product, such as fries, he doesn’t recommend trying to test used frying oil. “I recommend testing the product that is fried in the used oil, which is a more relevant sample in any case and probably more amenable to analysis,” he adds.

Detecting gluten in hydrolyzed or fermented foods also remains a problem, he adds, referring to the recent FDA 2020 final rule on the recommended approach to mitigating this problem by testing the food matrix before fermentation or hydrolysis.

Effective as of October 13, 2020, the FDA final rule establishes compliance requirements for labeling “gluten-free” fermented and hydrolyzed foods or foods containing fermented or hydrolyzed ingredients. “Because gluten proteins in hydrolyzed and fermented foods are no longer intact and, currently, cannot be adequately detected and quantified through testing, the FDA will determine compliance based on records kept by the manufacturer to show that their foods are gluten free before fermentation or hydrolysis,” says an FDA spokesperson, who underscores that the ruling doesn’t change FDA’s definition of “gluten free,” established in 2013. “[This] means that hydrolyzed and fermented foods bearing the gluten-free claim would still need to meet the requirements of the gluten-free final rule,” the spokesperson adds.

Manufacturers are required to comply with the rule by August 13, 2021.

In-House versus Third-Party Testing?

One decision that manufacturers will have to make is whether to conduct gluten testing in house or employ a third-party lab. Charles McGuill, product manager for allergens at Hygiena in New Braunfels, Texas, says that food companies normally don’t conduct just one type of testing, but will perform multiple tests. “They may use rapid technology where they can get a pass or fail test that gives them an idea if they have an allergen in their product, in their environment, or in the incoming raw ingredients they are using in their production facility, and then may use a third-party laboratory to send the finished product to make sure it is truly free of allergens,” he says, adding that some customers will require a certification of analysis from a third-party lab.

Most food production companies that want to test in house will use the lateral flow technology (pass/fail) test, he says, given how easy it is to use. Tests provided to food companies are calibrated to detect gluten at the restricted level of 20 mg/kg to 100 mg/kg. Hygiena also offers a lateral flow test that can be adjusted to detect levels above or below this, which, says McGuill, offers customers the flexibility of testing a finished product or ingredient that, for example, might be a microingredient used in the product.

McGuill also underscored the usefulness of current testing with the antibody assays as a screening tool but noted that they are limited when it comes to products that are highly processed, such as fermented or hydrolyzed products. “Customers should be aware that when they are testing complicated products, they should make sure to do their proper research and make sure the method they are using can properly identify the target,” he adds. “Do your homework.”

Dr. Rustgi underscored the need for food production companies to ensure their products are gluten-free; he would like to see a more concerted international effort among countries to comply with a single standard or set of regulations given free trade and tourism. “Similar standards and detection methods need to be adopted across industry and throughout the globe,” he says.