Celiac Disease is a life-long intolerance to the gliadin fraction of wheat and the prolamins of rye (secalins), barley (hordeins) and possibly oats (avidins). The condition is the end result of three processes: Genetic predisposition, environmental factors and immunogically-based inflammation that culminate in intestinal mucosal damage. Sufferers have small intestine inflammation that leads to malabsorption of nutrients such as iron, folic acid, calcium and fat-soluble vitamins. The only effective treatment is strict adherence to a gluten-free diet throughout life, resulting in mucosal recovery.
A gluten-free diet excludes foods made with wheat, rye, barley, triticale, dinkel, kamut and oat flour as well as by-products made from those grains. Other excluded foods are those that use wheat- and gluten-derivatives as thickeners and fillers, for example, hot dogs, salad dressings, canned soups/dried soup mixes, processed cheese and cream sauces.
Prevalence and LabelingEpidemiological studies in 1950 first estimated relatively low incidences of Celiac Disease. However, by the 1960s, more specific tests became available and it is now possible to determine accurately the true prevalence. While a biopsy remains the definitive test, antigliadin antibody serological tests have resulted in substantially increased diagnosis rates. Screening with modern serological tests places incidence of Celiac Disease in the U.S. at 1/111.
The iceberg model often is used to explain prevalence (See chart “The Tip of the Iceberg”). Properly diagnosed cases form a small, visible tip while many more “silent” cases exist.
In 1976, the Codex Alimentarius Commission of the World Health Organization (WHO, Geneva) and the Food and Agricultural Organization (FAO, Rome) adopted The Codex Standard for gluten-free foods. In 1981 and in 2000, draft-revised standards stated that so-called “gluten-free foods” are described as: (a) consisting of, or made only from ingredients which do not contain any prolamins from wheat or all Triticum species such as spelt, kamut or durum wheat, rye, barley, oats or their crossbred varieties with a gluten level not exceeding 20ppm; or (b) consisting of ingredients from wheat, rye, barley, oats, spelt or their crossbred varieties, which have been rendered gluten-free; with a gluten level not exceeding 200ppm; or (c) any mixture of two ingredients as in (a) and (b) mentioned with a level not exceeding 200ppm.
In this context, the WHO/FAO standard gluten was defined as a protein fraction from wheat, rye, barley, oats or their crossbred varieties (e.g., Triticale) and derivatives thereof, to which some persons are intolerant and that are insoluble in water and 0.5M NaCl. Prolamins are defined as the fraction from gluten that can be extracted by 40%-70% aqueous ethanol. The prolamin from wheat is gliadin, from rye is secalin, from barley is hordein and from oats is avenin. The prolamin content of gluten is generally taken as 50%.
However, there are discrepancies in labeling foods “gluten-free” because the exact amount of prolamins that individuals with Celiac Disease may consume without damaging the mucosa has not been scientifically determined. It had been thought that the protein component in wheat starch could be completely removed, but it is now known that some protein will remain. In the U.S. and Canada, gluten-free diets are devoid of any wheat starch, and are based on naturally gluten-free ingredients such as rice.
Formulating Gluten-free, Cereal-based ProductsOn a dry matter basis, gluten contains 75%-86% protein (as glutenin and gliadin fractions). The remainder is made up of carbohydrates and lipids that are held strongly within the gluten-protein matrix. Upon full hydration, glutenin is a rough, rubbery mass, while gliadin produces a viscous, fluid mass. Gluten, therefore, exhibits cohesive, elastic and viscous properties that combine the extremes of the two components. The gluten matrix is a major determinant of the important properties of dough (such as extensibility, resistance to stretch, mixing tolerance and gas-holding ability), which encloses the starch granules and fiber fragments.
Gluten can be termed the “structural” protein in bread. Its absence often produces a liquid bread batter rather than dough. The final baked bread may have a crumbling texture, poor color and other quality defects. One researcher concluded that bread dough without gluten could only retain gas if another gel replaces the gluten. In pasta, gluten contributes to a strong protein network that prevents product dissolution during cooking.
Additional difficulties occur when alternative gluten-free ingredients are used, since modifications to traditional production processes may be required. One exception is in the manufacture of gluten-free cookies. The development of a gluten network in cookie dough is minimal and undesirable (apart from certain semi-sweet cookies, which may have a developed gluten system); the texture of baked biscuits cookies is primarily attributable to starch gelatinization and super-cooled sugar rather than a protein/starch structure.
The formulation of gluten-free bakery products presents a formidable challenge to both the cereal technologist and the baker. Recently, there has been significantly more R&D on gluten-free products, resulting in diverse approaches. These include the use of starches, dairy products, gums and hydrocolloids, and other non-gluten proteins and prebiotics as gluten alternatives to improve the structure, mouthfeel, acceptability and shelflife of gluten-free bakery products. Extensive R&D is ongoing at the authors' laboratories at The National Food Centre (Dublin, Ireland) and at University College (Cork, Ireland) in a joint project using a “bioengineering” approach. This term describes the building of texture in gluten-free, cereal-based products using a range of ingredients.
Starches and GumsStarches and hydrocolloids are widely used in baked goods to impart texture and appearance properties. These are useful for gluten-free products as well.
An early study published in 1954 on the role of starch in breadmaking showed that breads could be prepared from starch and gel-forming substances. Rice starches offer an option in that they do not have gluten, have low levels of sodium and have high amounts of easily digested carbohydrates, which are desirable for special diets. However, the absence of gluten causes problems in breadmaking. A 1997 study showed that many gum types including hydroxypropylmethylcellulose (HPMC), locust bean, guar, carrageenan, xanthan and agar successfully formed rice bread. HPMC gave optimum volume expansion. A 2001 study found that 1.7% HPMC and 0.4% carboxymethylcellulose (CMC), as gluten substitutes, contributed better bread characteristics than 0.7% guar gum in a 50:50 wheat flour/rice flour formulation. The researchers also concluded that replacing 30% of the wheat flour with rice flour was the maximum possible level for acceptable bread quality without the addition of a gluten substitute, and brown rice flour was unsuitable for baking rice bread. In another paper, researchers found that fine white and ground rice flours gave good quality, gluten-free breads when used in combination with 0.8% CMC and 3.3% HPMC.
Two papers published in 1996 investigated the use of different binding agents (xanthan, guar gum, locust bean gum and tragant) as a gluten substitute in gluten-free bread formulations based on cornstarch. The binding agents resulted in a highly significant increase in loaf volume and loosening of the crumb structure. The highest quality, gluten-free bread contained xanthan gum at levels of 1%-3%.
An early 1975 article discussed the application of soy protein in the manufacture of gluten-free breads. The authors formulated wheat starch-based gluten-free breads with 20%, 30% and 40% soy protein isolate (containing 88% protein). The breads had more protein and fat than wheat bread, and showed satisfactory baking characteristics. The authors of a 2000 article on the production of gluten-free breads and other baked goods in South America used fermented cassava starches. By increasing the proofing time of gluten-free bread dough (based on potato/corn/rice starches, pectin, emulsifiers and lactose-free margarine), one author of a 1980 article obtained high-quality gluten-free yeast breads and gingerbreads.
Gums and thickeners are used for a variety of purposes, including gelling and thickening, water retention and texture improvement. A study published in 1996 used combinations of guar gum and locust bean gum to partially replace flour in bread. The use of guar gum resulted in a crumb structure with a more even cell size distribution, while locust bean gum inclusion increased bread loaf height. Both gums retarded bread staling. Optimum levels for locust bean gum and guar gum were 2%-4%.
A study published in 2002--whose authors included two from this article-- investigated the application of novel rice starches (manufactured with low to high degrees of starch hydrolysis) on a replacement basis for wheat starch in gluten-free bread formulations. The inclusion of the rice starches at 3%-9% levels resulted in gluten-free loaves with less yellow crumb appearance (Minolta b* value), and darker crust colour (Minolta L*). Crust hardness was unaffected, but crumb hardness (measured by Texture Profile Analysis) was reduced, as was the rate of staling. The optimum level for rice starch inclusion was 6%; this also doubled the dietary fiber content of the loaves. Extensive tests also are being carried out at University College (Cork, Ireland) on the formulation of gluten-free loaves based on corn, potato, buckwheat, with blends of gums and dairy ingredients.
Dietary FiberDietary fiber's role in contributing to a healthy intestine has long been recognized. Since gluten-free products generally are not enriched or fortified and frequently are made from refined flour or starch, they may not contain the same nutrient level as the gluten-containing counterparts they are replacing. Celiac patients living on gluten-free products may not be ensured a nutritionally balanced diet. In one recent study, researchers screened the intake of nutrients of 49 adults diagnosed with Celiac Disease that were following a gluten-free diet. They were found to have a lower intake of fiber compared to a control group of people on a normal diet. Several research studies, including one on celiac adolescents, concluded that adherence to a strict gluten-free diet worsens the already nutritionally unbalanced diet of adolescents (their dietary levels of nutrients and fiber were found to be low).
Enriching gluten-free baked products with dietary fibers is an interesting topic of research. Inulin acts as a prebiotic by stimulating the growth of “healthy” bacteria in the colon. When added to wheat bread, it improves loaf volume and sliceability, increases dough stability and produces a uniform and finely grained crumb texture. Two authors of this article incorporated inulin (8% inclusion level) into a wheat starch-based, gluten-free formulation. The bread's dietary fiber content increased from 1.4% (control) to 7.5% (control with added inulin), and crust color also was enhanced. The latter was due to the enzymes in the yeast hydrolyzing part of the inulin, resulting in the formation of fructose and causing crust browning.
In a study published in 2002, amaranthus flour replaced cornstarch to enhance the protein and fiber contents of gluten-free breads. At a 10% replacement level, protein and fiber levels increased by 32% and 152% respectively, while sensory quality was unaffected. Another 2002 paper discussed the application of quinoa as a novel application in the production of enriched, gluten-free bakery goods. An older 1996 article described the use of amaranth in gluten-free products. The researchers formulated a gluten-free mix using wholemeal amaranthus flour. Both quinoa and amaranth are “pseudocereals” that have a high nutritional value. One study looked at both quinoa and amaranth as a 40% replacement for wheat flour in a yeast bread formulation. The bread quality (loaf volume and crumb softness) and nutritional aspects, including dietary fiber content, were improved when the dough moisture was increased to 65%.
Dairy IngredientsDairy proteins may be used in bakery products for both nutritional and functional benefits--including flavor and texture enhancement, and storage improvement. Dairy products may be used in gluten-free bread formulas to increase water absorption and, therefore, enhance the handling properties of the batter. However, supplementation of gluten-free breads with high lactose-content powders is not suitable for celiacs who have significant damage to their intestinal villi; they may be intolerant to lactose due to the absence of the lactase enzyme, which is generated by the villi.
In a study published in 2003, the authors of this article applied seven dairy powders to a gluten-free bread formulation. In general, the powders with a high-protein/low-lactose content (sodium caseinate, milk protein isolate) gave breads an improved overall shape and volume, and a firmer crumb texture. (See chart “Dairy Proteins and Loaf Volume.”) The breads had an appealing dark crust and white crumb appearance, and received good acceptability scores in sensory tests. When optimal water was added to the gluten-free formulation, the breads exhibited increased volume and a much softer crust and crumb texture than the controls. Supplementing the gluten-free formulation with high protein-content dairy powders doubled the protein content of the breads.
Other ToolsOne statistical tool, response surface methodology (RSM), is particularly useful for product development. A study published in 1991 used RSM to evaluate gluten-free breads based on three types of rice flour. Optimal loaves were formulated with medium-grain, finely ground rice flour, low levels of HPMC and low levels of CMC. A second trial used the same rice flours, but the breads were based on formulas of 80% rice flour and 20% potato starch. Using sensory measurements from a trained panel, RSM was used to find optimal CMC, HPMC and water combinations for the different rice flours. Gluten-free loaves made with medium-grain rice flours were of a higher standard with respect to moistness, cohesiveness, flavor, color and cell structure than those made from long-grain rice flour.
Another study investigated optimal proportions of cornstarch, cassava starch and rice flour in gluten-free breads that also had 0.5% soy flour for improved bread crumb characteristics. The optimal formulation was calculated as 74.2% cornstarch, 17.2% rice flour and 8.6% cassava starch. Unusually large gas cells were rectified by the addition of soy flour.
RSM has been employed at the authors' laboratory at The National Food Centre (Dublin, Ireland) to develop and optimize a gluten-free bread formulation based on rice flour, potato starch, skim milk powder and HPMC. (See chart “Optimizing a Formula.”)
RSM has been used to analyze the effects of methylcellulose, gum arabic and egg albumen on the sensory properties of gluten-free flat breads based on corn flour and pre-gelatinized rice flour and cornstarch. Methylcellulose and egg albumen were the major determinants of product sensory quality.
A novel approach at The National Food Centre (Cork, Ireland) looked at supplementing a control gluten-free bread formula based on rice flour and potato starch with fish surimi at a 10% level (of starch weight). Surimi, a concentrate of myofibrillar proteins, is a highly functional ingredient with excellent gel-forming properties. Frozen surimi of four species was evaluated. Texture profile analysis (post-baking) indicated that three of the surimi breads had a softer (P<0.001) crust and crumb than the controls. These breads also revealed higher (P<0.001) loaf volumes than the controls.
The greater awareness of the prevalence of Celiac Disease will continue to drive interest in gluten-free products. A common approach is to use a variety of ingredients to mimic gluten. However, more research is needed in this area.
The original, heavily referenced article has been condensed and adapted by Claudia Dziuk O'Donnell, Chief Editor, Prepared Foods from the following source: Trends in Food Science & Technology, Volume 15, E. Gallagher1, T.R. Gormley1 and E. K. Arendt2, Recent Advances in the Formulation of Gluten-free Cereal-based Products, Pages 143-152, Copyright 2004 with permission from Elsevier. www.sciencedirect.com/science/journal/09242244
Sidebar: Referenced Pizza, Pasta and Cookie InformationOne paper (Huang JC, et al., 2001. Journal of Food Quality, 24, p. 495) reported on a study where non-gluten pasta had sensory properties and pasta stickiness closest to wheat-based pasta when higher levels of modified starch, xanthan gum and locust bean gum were used. In 1999, Wang N, et al. (Journal of Food Science, 64, p. 671) found that pasta of 100% pea flour and made on a twin-screw extruder exhibited improved texture and flavor after cooking, when compared with the same product prepared using a conventional pasta extruder.
The effects on a gluten-free cookie formulation using six different starch sources in combination with four different types of fat sources was studied by Arendt EK, et al. (2002, Farm and Food, 12, p. 21). Among other findings, rice, corn, potato and soy with high-fat powders produced sheetable cookie doughs that resulted in finished products of comparable quality to wheat-based cookies. They also found that cornstarch, guar gum and high-fat powder produced acceptable gluten-free pizza bases.
In 1996, Tosi, E.A., et al. (Alimentaria, 34, p. 49) reported that the addition of 0.1% BHT to the fat for gluten-free cookies of wholemeal amaranthus flour extended the shelflife without enhancing [changing] flavor.