Technical Talk – July 2009

Continuing our series on the basic components and processes of baking, what ingredients are available to help us produce gluten-free baked goods and how do they function in dough systems?

Celiac disease (CD) is a condition caused by an intolerance to some cereal gluten proteins – namely, gliadin in wheat, secalins in rye and hordeins of barley. CD sufferers, also known as celiacs, who ingest gluten will experience inflammation and mucosal damage of the small intestine.

Red quinoa grain can be used to make a gluten-free baking flour.

About 0.9 to 1.2 per cent of the Western population suffers from CD, but this number has been growing in recent years. The only effective treatment for CD is complete removal of gluten from the diet; this means avoiding wheat, durum, spelt, kamut, rye, barley and triticale. Oats should also be avoided as they are often contaminated with gluten-containing cereals.

Fortunately, a growing number of gluten-free (GF) baking ingredients enable us to produce acceptable-quality baked goods, but these need to be supplemented with some important minor components to perform reasonably well in baking systems. Typical GF formulations use corn, potato and rice flours. Flours from amaranth, buckwheat, millet, quinoa, soybean, sorghum, beans, peas, chickpeas and lupin are also being used.

The lack of gluten in GF flours results in poor structure in the final product. GF bread doughs are soft and batter-like, so the breads are more susceptible to collapse, resulting in large holes in the centre of the bread crumb and dense areas at the bottom of the crumb.

Furthermore, shaping gluten-free doughs into pretzels, baguettes or braided breads is practically impossible. Ingredients must be added to mimic the gluten matrix in order to create a GF product comparable to the gluten-containing version. Such ingredients include hydrocolloids (gums), enzymes and specialized starches.

Hydrocolloids are added as structuring agents to replace the function of the gluten matrix. Such additives include carboxy-methylcellulose (CMC), hydroxypropylmethylcellulose (HPMC), xanthan gum and guar gum. Pectin, gum arabic and galactomannans can also be used.

Hydrocolloids interact with water to reduce its diffusion and increase its stability; this can be accomplished by binding water or physical entrapment. This increases the viscosity, which affects the product’s texture and processing characteristics. The increase in viscosity also allows for the entrapment of fermentation gases, and the “water-release” effect required for starch gelatinization during baking, thereby improving cell structure and volume.

Xanthan gum and HPMC appear to mimic gluten properties the best, and are used most often; because they seem to have a greater ability to retain water, freshness is maintained longer. In particular, the pseudoplastic behaviour of xanthan gum is helpful during dough preparation. Also, interactions between gums can result in synergistic effects that improve dough viscosity, depending on gum ratio, mixing temperature and ionic strength.

The poor nutritional value of GF products has driven the interest in alternative healthier ingredients. For example, beta-glucan is a hydrocolloid rich in soluble dietary fibre with additional heart health benefits. Resistant starch is a prebiotic and behaves like a soluble dietary fibre. Both can improve gastrointestinal health and blood cholesterol levels, and help control diabetes. They also play a functional role in the formulation of GF products.

Certain enzymes show great potential for improving the performance of GF flours in baked goods, while some research suggests that other microbial enzymes may break down the gluten to levels that are not harmful.

The most promising enzyme being investigated is Transglutaminase (TG), which cross-links different proteins that contain the amino acids glutamine and lysine. The efficiency of the enzyme depends on the protein source and the level of enzyme concentration.

Buckwheat flour works well with TG to significantly improve the texture and structure of the resulting breads. This is likely due to the high incidence of glutamine and lysine amino acids in buckwheat protein. In contrast, TG reduced elasticity in corn flour bread. Its effect is also being investigated with various pulse flours. Overall, TG increases specific volume and decreases crumb hardness and chewiness.

The addition of cyclodextrinase to rice flour dough improves the bread’s volume, shape and texture. Used as an improver, this enzyme forms cyclodextrins, which can form complexes with lipids and proteins. Alpha-amylase may be added to break down starch for the yeast and to increase dextrin content in the dough.

Peptidases can be used to break down gluten into fragments. They have a short degradation time, degrade peptides and proteins, and are highly active at a wide temperature and pH range.

Proteolytic bacteria are another source of peptidases. For instance, Lactobacillus sanfranciscensis LS40 and LS41 and Lactobacillus plantarum CF1 are sourdough strains that can break down gluten and may eliminate the problem of gluten contamination in GF bread. Enough degradation can be achieved to result in less than 20 parts per million of gluten in the final product. (Less than 20 parts per million is the threshold level assigned by bodies such as the World Health Organization for foods that are naturally free of gluten.)

Bacteria in sourdough may also improve the quality and shelf life of gluten-free bread. For example, adding Lactobacillus plantarum FST1.7 to the gluten-free bread dough increased firmness and elasticity. A research study showed that using a sourdough fermentation improved the structure of a gluten-free sorghum bread that included HPMC (two per cent).

Common emulsifiers can also be added to GF formulations as they can increase the specific volume. Different emulsifiers and different usage levels have varying effects on cell size and distribution. Egg or dairy proteins can be added for their emulsifying and foaming properties, and to improve nutritional quality.
 
Processing methods can also affect the quality of the GF product. For example, extrusion of rice flour (15 per cent moisture) improves bread volume and crumb structure quality (versus non-extruded rice flour). In another study, extrusion of a corn meal and soybean flour blend (75/25) with the addition of guar gum resulted in the biggest volume, best crumb elasticity, softness, and porosity of finished product. This may be attributed to the starch gelatinization during extrusion, which can improve functional properties and provide body.

The use of pulse flours in GF formulations is gaining interest, as they provide improved functional and nutritional benefits. Bean flours made from a variety of different beans are available. Their high protein and fibre content improves the nutritional quality of gluten-free breads. Furthermore, they provide suitable proteins that can be strengthened by transglutaminase. Pea and soy proteins offer similar benefits.

Psyllium fibre forms a film-like structure, and combined with a continuous protein phase, it acts as an improver of the cohesion of the starchy matrix (even though more water is required in the formula) and improves the dough’s workability and bread quality. Carob germ contains gluten-like proteins called caroubin that can form viscoelastic material like wheat gluten.

Additionally, specialized gelatinized starches show promise in being low-cost ingredients capable of forming three-dimensional networks that retain gases and expand during fermentation and baking.

GF bakery products currently on the market have a lot of room for improvement. As more consumers are diagnosed with celiac disease, they will demand GF products that are comparable to their gluten-containing counterparts. The use of hydrocolloids, novel grains, enzymes and other specialized ingredients offers many possibilities to meet and hopefully exceed this demand.

Funding for this report was provided in part by Agriculture and Agri-Food Canada through the Agricultural Adaptation Council’s CanAdvance Program.

Dr. John Michaelides is Guelph Food Technology Institute’s director of research and technology. His colleague Adrienne Shrum co-wrote this month’s column. For more information, or fee-for-service help with product or process development needs, please contact GFTC at 519-821-1246 or  gftc@gftc.ca.