Improving gluten-free dough by a novel hemicellulose network

Globally high numbers of patients suffering from coeliac disease and gluten-sensitivity call for high-qualitative gluten-free daily foods, particularly bread. Currently, gluten-free breads still lack behind. Primarily, their nutritional profile is often poor since they are mainly based on pure starches. Secondly, their sensory properties are inferior. Moreover, several technological problems arise due to the absence of gluten. Millet and sorghum as well as the pseudocereals amaranth, quinoa and buckwheat are known to have several nutritional benefits compared to commonly used bread cereals and therewith could diminish deficits of CD-patients. Indeed, some approaches towards improvement of gluten-free bread have been revealed so far, e.g. addition of hydrocolloids, emulsifier, enzymatic treatments or sour- dough fermentation. However, achieved results are insufficient and until now it is not possible to fully imitate a gluten-network. The objective of the supposed project is to combine several helpful approaches and facts in order to develop high quality gluten-free bread. Rye pentosans have the highest molecular weight and therefore a very high viscosity. Therefore rye-AX are very promising for application as baking improver in gluten-free bread. The main idea is to apply customised rye-bran pentosans combined with tailored pentosan-crosslinking enzymes (Laccase, Glucose-oxidase and Pyranose-oxidase) in mentioned (pseudo)cereals. It is presumed that this should result in an enormous network comparable to gluten within a healthy matrix. The potential of AX as natural bread improver was already demonstrated for wheat/rye breads and hence, also isolation trials of AX out of flours were conducted. However, up to now, yield, purity, and cost efficiency of all published processes are not satisfying. A pilot- scale isolation process of AX-fractions out of rye bran was recently developed at BOKU. That process holds the highest reported yield, superior economic benefit since using bran (food industry by-product) as raw material and avoids organic solvents due to the application of ultra-dia-filtration. However, there is still space for further improvement which will be addressed within the project. Particularly, the process will be further upgraded by implying various xylanase-preparations to tailor the resulting AX for bread making purposes. Although production of required enzymes is state-of-the-art, commercial Laccase- preparations are only available with several limitations (purity, activity). But many laccases with different activities and working optima are known. Therefore, also improvement of production and isolation of required enzymes with targeted characteristics for bread-making purpose (specifity, side-activities) will be an objective of the project. In consequence, the interaction of various gained rye AX and different enzyme preparations should be studied initially in a simplified system. The effect of respective sophistically pentosan and enzyme preparations on the quality of selected sour-dough systems will then be investigated by rheological and chemical analyses. Baking trials and sensory tests will finally complete the project.

Gluten is the main structure forming protein in wheat bread that confers the dough its specific properties and baking quality. Due to its unique functionality, the replacement of gluten is challenging. In rye bread it is the arabinoxylans (AX), which are soluble and insoluble dietary fibers found naturally in cell walls of cereal grains, that are mainly involved in dough structure development by formation of arabinoxylan networks. Aim of this study was therefore to imitate this rye bread structure in gluten-free (GF) bread by adding isolated rye arabinoxylans. For this purpose, a range of different technologies to extract arabinoxylans from rye bran, to apply enzymes and sourdough fermentation for an increased network formation were fundamentally studied, with the aim to obtain an appropriate and stable AX- network and consequently a high quality GF bread. All these experiments were performed in close cooperation with the Budapest University of Technology and Economics (BME), Department of Applied Biotechnology and Food Science. After thorough and comprehensive extraction experiments applying an environmentally friendly and economically feasible process the yield of isolated arabinoxylans could be optimized to 3.81 g AX/100g rye bran while attaining good functionality of the AXs at the same time. During detailed and exhaustive rheological and baking experiments the produced arabinoxylans were investigated for its ability to improve the structure of GF bread. By optional addition of the enzyme pyranose-2-oxidase and adapted sourdough fermentation the arabinoxylans, which were alkaline extracted with calcium-hydroxide, showed most promising results. The performed study successfully demonstrated, that arabinoxylans extracted from rye bran offer a natural, environmentally and consumer friendly alternative to (artificial) hydrocolloids (e.g. HPMC), that are able improve the quality of GF breads.