Over the past decade, the demand for gluten-free food has soared, and more and more of these products can now be found in stores. The number of consumers who have difficulties with digesting gluten has grown to around 10%.
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These individuals show varying degrees of sensitivity toward gluten, but their situation generally improves when they follow a gluten-free diet. Furthermore, increasing numbers of consumers believe that a gluten-free diet is more healthful. But what is gluten? How can it be toxic? And how can gluten be detected in food?
What Is Gluten?
The name “gluten” is derived from the Latin word for glue, and it refers to the composite of the proteins called prolamins and glutelins, found in wheat, barley, rye, oats, and their crossbred varieties. Prolamins are defined as the fraction that can be extracted using 40-70% of ethanol, and this fraction is called gliadin, hordein, secalin, or avenin, respectively, depending on the grain variety. In general, prolamins and glutelins are estimated to occur in the same ratio in gluten.
Worldwide, gluten is an important source of nutritional protein, both in foods prepared directly from gluten-containing sources and as an additive to foods otherwise low in protein. Gluten contributes texture and form to food products, due to its physicochemical properties. Mixed with water and kneaded, gluten forms a viscoelastic dough with a special protein network, which is responsible for the shape of bakery products.
Since the transition from the hunter-gatherer lifestyle to the beginning of agriculture 10,000 years ago, cereals have been a main pillar of the human diet, which raises the question of why gluten is causing increasing levels of health problems now. Approximately 1% of the world’s population is affected by celiac disease, an immune-mediated enteropathy caused by the ingestion of gluten.
Interestingly, the condition occurs more frequently in women than in men. Symptoms are diverse and not confined to the gastrointestinal tract. Examples include not only diarrhea, abdominal pain, flatulence, indigestion, and weight loss, but also irritability, depression, and anxiety. However, all these symptoms are considered to be unreliable as an indicator for the disease. Celiac disease can be diagnosed by screening for certain antibodies in the serum.
Another recommended diagnosis involves a biopsy of the mucosa and the small intestine to affirm damage, because the disease leads to the destruction of villi, microscopic, finger-like projections in the small intestine. Because intestinal villi are responsible for the absorption of nutrients, malnourishment may occur and, if it continues on a long-term basis, may lead to developmental delays, osteoporosis, or nutrient deficiencies, along with other problems.
Celiac disease, in which the immune system responds inappropriately to dietary gluten, is an autoimmune disorder to which people can be genetically predisposed. The enzyme called tissue transglutaminase modifies gluten peptides by deamidation so that T-cell epitopes are formed. This stimulates the immune system and cross reacts with the small intestine tissue, causing an inflammatory reaction that leads to the truncation of the villi. The majority of proteins responsible for such an immune reaction are prolamins. The strongest response is directed toward a 2-gliadin fragment that is 33 amino acids long, and is a principal contributor to gluten immunotoxicity. This so-called 33-mer is highly resistant to breakdown by digestive enzymes and is, therefore, a suitable molecule for use as an analytical marker. Homologues that have been found in food grains that are toxic for celiac patients are absent in nontoxic grains.
The only effective treatment for celiac disease up to now has been a lifelong gluten-free diet. Unfortunately, gluten is found in most foods, making this diet challenging to maintain. “Hidden” gluten used as a protein filler can be found in unexpected products such as pharmaceuticals, sausages, sauces, and desserts. In addition, gluten-free products may contain gluten due to cross contamination during milling, storage, and production. Gluten-free food is usually based on rice, maize, or buckwheat, as well as purified starch that contains low levels of gluten. It is very difficult to set limits, because sensitivity varies from individual to individual. According to scientific studies, the ingestion of gluten should be maintained at a level below 50 mg per day.
Legislation and Standards
The Codex Alimentarius Commission started to discuss recommendations for limits in the late 1970s, culminating in the 2008 CODEX Standard for Foods for Special Dietary Use for Persons Intolerant to Gluten (CODEX STAN 118 – 1979). This recommendation was taken into European legislation through Commission Regulation (EC) No 41/2009 of 20 January 2009, concerning the composition and labeling of foodstuffs suitable for people intolerant to gluten. In contrast to other food allergens, thresholds for glutens have been defined. Food labeled as gluten-free must not exceed 20 ppm, whereas food containing low levels of gluten must be lower than 100 ppm. A proposed rule for gluten-free labeling of foods is in preparation in the U.S.