Testing for Gluten in Foods Neil H. Mermelstein | February 2011, Volume 65, No.2


People who suffer from celiac disease must avoid consumption of foods containing gluten, and the food industry is responding to this need by marketing an increasing number of gluten-free products. Manufacturers of such products must not only formulate their products without gluten but also check that there is no cross-contamination from other products and processes. This article will discuss gluten sensitivity, the available analytical tests for detecting gluten in food products, regulatory concerns, and challenges ahead for the food industry.

Pasta made from durum wheat has a high content of gluten and is therefore one of the foods that must be avoided by people with celiac disease.Gluten Sensitivity
Gluten is a mixture of prolamin (gliadin in wheat) and glutelin proteins naturally present in wheat, rye, barley, and related grains, including those wheat varieties known by such names as durum (semolina), spelt, einkorn, emmer, khorasan (Kamut), club wheat, triticale, and farro. It is most commonly present in products made from wheat flour and in certain other food products in which it is used as an ingredient, providing elasticity in baked goods, for example, as well as texture, moisture retention, and flavor.

Celiac disease, also referred to as celiac sprue, is a genetic disease that is said to affect about 1% of the people in North America and Europe. The immune system of people with the disease responds to the consumption of gluten by damaging the lining of the small intestine, thus interfering with absorption of nutrients. The disease has no cure but can be managed by avoiding gluten in the diet.

The number of products marketed as gluten-free is increasing worldwide, but even with the establishment of regulations allowing such labeling, it is possible that foods labeled as gluten-free may be contaminated during processing by equipment previously used for gluten-containing foods. Because of the high prevalence of wheat in the food supply, even products that are formulated or processed to not contain it may still contain enough trace amounts of gluten to produce symptoms in gluten-sensitive individuals. Consequently, reliable tests are required for the detection of gluten in foods.

Detection Methods
The majority of tests for gluten in food products are enzyme-linked immunosorbent assays (ELISAs). Microwell versions of ELISAs provide quantitative results. Lateral-flow devices generally provide qualitative results, indicating the presence of gluten above a threshold level, but in some instances can also provide semi-quantitative results. Other types of tests include polymerase chain reaction (PCR), which detects DNA rather than protein; adenosine triphosphate (ATP) swab tests for assessing cleanliness of equipment surfaces; and general protein swabs, which are not specific to gluten but detect all types of protein and can be used for assessing cleanliness. (See diagram for microwell illustration.)

Testing for Gluten in Foods
Example diagram of microwell sandwich ELISA

ELISAs are far more specific than the other methods, according to Steve Taylor, Professor in the Dept. of Food Science & Technology at the University of Nebraska-Lincoln, and Director of the Food Allergy Research & Resource Program (www.farrp.org) at the university. ATP testing usually won’t work for gluten if there are other sources of ATP present but is good for general cleanliness. A result positive for ATP would usually also mean positive for gliadin, but a result negative for ATP would not necessarily mean negative for gliadin because ATP tests are not as sensitive as ELISAs. The same comments apply to general protein tests, which are also not as reliable if other sources of protein are present.

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