Michael G. Gänzle, University of Alberta, Dept. of Agricultural, Food, and Nutritional Science, 4–10 Ag/For Centre, Edmonton, AB, Canada T6G 2P5, Phone +1-780-492-0774, fax +1-780-492-4265, e-mail firstname.lastname@example.org; Clarissa Schwab, University of Alberta, Dept. of Agricultural, Food, and Nutritional Science, 4–10 Ag/For Centre, Edmonton, AB, Canada T6G 2P5
The Science of Gluten-Free Foods and Beverages
The treatment of coeliac disease (CD) requires the lifelong avoidance of the ingestion of prolamins of the Tricitum species such as wheat, rye, kamut, spelt, and barley. However, rye and particularly wheat are considered to be the only cereal grains suitable for the production of bread, a staple food in Western diets. The production of gluten-free breads for coeliac patients with acceptable sensory and nutritional properties remains a major challenge because wheat gluten exhibits multiple functionalities in the bread making process: (i) gluten proteins are major contributors to the water holding capacity of the dough and water bound by gluten proteins becomes available for starch gelatinization during baking; (ii) the formation of the gluten network determines the visco-elastic properties of doughs, and is relevant for gas retention during dough fermentation; (iii) gluten-associated proteinases liberate peptides and amino acids that are relevant as taste compounds as well as precursor compounds for bread flavour. In rye baking, dough hydration and gas retention are mediated by water-soluble pentosans because rye secalins do not form a polymeric protein network. The resulting breads are not inferior with respect to flavour and taste, but have a smaller specific loaf volume and a denser crumb structure when compared to wheat breads. Gluten-free bread formulas require multiple ingredients to substitute for wheat gluten and commonly include a protein source (e.g., soy protein or dairy proteins), raw or pre-gelatinized starch, hydrocolloids, and flour from non-toxic cereals (maize, rice, sorghum, millets, and tef) or pseudo-cereals (buckwheat, amaranth, cassava, and quinoa). Nonetheless, many of the gluten-free products that are currently available are of poor sensory and nutritional quality when compared to the conventional counterparts.
The metabolic potential of lactic acid bacteria (LAB) is used in sourdough fermentations to improve flavour, texture, and shelf life in conventional baked cereal products. However, sourdough fermentations are not widely applied in the production of gluten-free bread. Katina et al. indicated in 2005 that published reports on the use of sourdough in gluten-free baking are essentially unavailable. More recent reports indicate that the use of sourdough improves flavour, texture, and shelf life in a manner comparable to the function of sourdough for conventional baking (Schober et al., 2007; Arendt et al., 2007). Fermented food products from rice, maize, sorghum, and other gluten-free cereals can be found in tropical climates, and several gluten-free cereal fermentations have been characterized on the microbial and biochemical levels (Nout and Sarkar, 1999; Hammes et al., 2005). This chapter gives an overview on the contribution of specific metabolic properties of LAB on the quality of gluten-free baked cereal products. Because of the limited knowledge of chemical, biochemical, and microbial conversions in gluten-free sourdoughs, this assessment relies on the effect of sourdough on conventional bread as well as on the biochemical and microbiological characterization of fermented cereal products that are traditionally produced from gluten-free flours.