Gluten detection in foods available in the United States – A market survey
Introduction
Gluten-free (GF) foods and beverages are becoming increasingly popular specialty foods in the US market with retail sales amounting to almost $1.6 billion in 2010 (Sapone et al., 2012). The growing consumer demand for GF foods has led to an increase in gluten-substituted food product development. In 2010, 10.8% of new foods and beverages contained GF health and nutrition-related claims, second only to high vitamin/mineral claims (12.2%) (Martinez, 2013). The rise in GF foods is partly due to increased awareness among individuals with celiac disease (CD), wheat allergy and gluten sensitivity, which requires these patients to follow a strict gluten-free diet. However, consumer perception of other benefits associated with a GF diet, such as digestive health, nutritive value, weight management, and high quality, also contributes significantly to increased sales of GF foods (Martinez, 2013).
Celiac disease is a cell-mediated autoimmune disease whereas wheat allergy is an immunoglobulin E (IgE)-mediated reaction. The symptoms of these disorders may vary, depending on individual sensitivity and disease severity. Celiac disease causes villous atrophy of the small intestine, resulting in various gastrointestinal and extraintestinal/systemic complications (Rallabhandi, 2012). Like other food allergies, depending on the severity, the symptoms of wheat allergy may range from mild itching to life-threatening anaphylaxis. Since there is no cure available, avoidance of gluten/wheat in the diet is the best option for patients. Both CD and wheat allergy are caused by the ingestion of wheat proteins. Gluten is the group of proteins causing CD, whereas major wheat allergens belong to the albumin/globulin group of proteins. Gluten also causes certain forms of wheat allergy, such as wheat-dependent exercise-induced anaphylaxis, in sensitive individuals (Bouchez-Mahiout et al., 2010, Matsuo et al., 2005). It is not surprising that the proteins from rye and barley are also implicated in CD (Vader et al., 2002), since they belong to the same Triticeae family as wheat. Additionally, rye and barley have a high degree of protein homology and immunological cross-reactivity with wheat allergens (Palosuo, Alenius, Varjonen, Kalkkinen, & Reunala, 2001). Hence, gluten refers to a heterologous group of proteins composed of prolamin and glutelin fractions from wheat, rye and barley. The prolamin fraction is alcohol-soluble and is known as gliadin (wheat), secalin (rye) or hordein (barley), depending on the source grain.
Consumers rely on the food claims/labels to purchase foods with or without a specific ingredient. Gluten can be unintentionally introduced into food due to cross-contact of inherently GF grain with wheat, rye and/or barley during harvest, transport or storage. Cross-contact during food manufacturing, when using shared equipment, can also result in the presence of gluten in inherently GF foods. The accidental presence of gluten in food may be safe for most consumers, but can result in severe reactions in gluten-sensitive individuals. Although there is scarce information on gluten-specific food recalls, a recent study by Gendel and Zhu (2013) ranked wheat as the second major food allergen, following milk, responsible for food allergen recalls. Wheat is one of the main sources of gluten in foods. Food regulatory agencies have labelling mandates to authenticate GF claims. A limit of 20 ppm of gluten is the threshold for a food to be labelled as “gluten-free”, a level agreed upon by several food regulating agencies, including Codex Alimentarius, the European Union, and the US Food and Drug Administration. Various gluten detection methods have been developed in recent years, based on enzyme-linked immunosorbent assay (ELISA) (Moron et al., 2008, Skerritt and Hill, 1990, Valdes et al., 2003), lateral flow device/dipstick (Allred & Park, 2012), polymerised chain reaction (Dahinden et al., 2001, Mujico et al., 2011, Sandberg et al., 2003) and mass spectrometry (Sealey-Voyksner et al., 2010, Tanner et al., 2013). ELISA remains the most commonly used method for gluten quantitation and several ELISA kits, based on different polyclonal and monoclonal antibodies, are commercially available.
It is important to evaluate the gluten content in foods for labelling compliance and consumer safety. Past research has focussed on specific food categories for assessment of gluten content, such as single ingredient foods (Dostalek et al., 2009, Koerner et al., 2011, Koerner et al., 2013, Thompson et al., 2010) or cereal foods (Gelinas, McKinnon, Mena, & Mendez, 2008). There is scarce information on gluten levels in other complex foods. The objective of this study was to determine the gluten content in various foods labelled GF and those not labelled as GF, but without gluten-containing ingredients. Previous work has shown acceptable gluten recovery with R5 monoclonal-based ELISA (R-Biopharm) and a proprietary polyclonal-based ELISA (Morinaga) in spiked (Geng et al., 2008, Sharma, 2012) as well as incurred (Sharma et al., 2013) food samples. Also, both ELISA methods have been validated by multi-laboratory evaluation and the R5-Mendez ELISA method has been suggested by Codex Alimentarius for determination of gluten in foods. Hence, these ELISA kits were used as the gluten detection methods in the current study.
Section snippets
Materials
Food samples were purchased from local grocery stores. Two different ELISA kits were used in the study: wheat protein sandwich ELISA (181GD; Morinaga Institute of Biological Science, Inc., Yokohama, Japan) and R5 monoclonal-based RIDASCREEN® Gliadin sandwich ELISA (R7001; R-Biopharm AG, Darmstadt, Germany). The monoclonal antibody A1 and the goat anti-mouse peroxidase conjugate were from Biomedal S.L. (Spain) and Sigma Chemical Co. (St. Louis, MO, USA), respectively.
Food samples
In total, 461 different food
GF labelled foods
In total, 275 GF-labelled foods were divided into 12 categories (Table 2). Among these categories, snack foods made up the greatest number (20% of total GF labelled foods), followed by baked foods (10.5% of total GF labelled foods). Though not all GF labelled foods that were available in the market were surveyed, our selection of representative foods was consistent with the recent report by Martinez (2013), where snack foods (16.3%) were the major food category to bear no-gluten related claims
Conclusions
In summary, 3.6% of GF labelled foods had a gluten content ranging from 5.8 to 554 ppm, of which 1.1% foods were above the regulatory threshold of 20 ppm of gluten. However, depending on the food category of the non-GF labelled foods, gluten was detected in 25.8% of foods, at levels ranging from 5.3 to 1566 ppm, with 19.4% of foods having a measured gluten content of greater than 20 ppm. The presence of oats in a majority of the foods with high measured gluten levels suggests that oats are a
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