The effect of thermal processing on soluble dietary fibre fraction in wheat

Introduction A very important aspect of food quality is related to the nutritional quality and the effect on consumers’ health. As a result of processing, many foods are deprived of some substances having great importance for health, among which is the dietary fibre (DF). DF has some beneficial physiological effects, such as improving the bulk motility, decreasing blood cholesterol and glucose, preventing constipation and cancer and prebiotic acting . The American Association of Cereal Chemists defined DF as the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine . DF includes polysaccharides, oligosaccharides, lignin and associated plant substances . Based on their water solubility, DF is classified as soluble dietary fibre (SDF) and insoluble dietary fibre (IDF) . The predominant water SDF in wheat is arabinoxylan (6-8%). The main polysaccharide constituents of wheat endosperm cell walls are arabinoxylans, whereas arabinoxylans and β-glucans predominate in wheat aleurone layers, and arabinoxylan and cellulose predominate in cell walls of pericarp/testa. The arabinoxylans are composed of arabinose and xylose in a branched structure. Soluble polysaccharides give viscous aqueous solutions. The viscous properties depend on molecular weight or molecule size (linear or branched), ionically charged groups, surrounding structures, and concentration of DF. In aqueous solutions, water molecules penetrate the amorphous regions of soluble DF. The increase in viscosity is explained by formation of Ca bridges and hydrogen bonds, resulting in a loose network that can hold considerable amounts of water 11, . Most food processing methods are essentially based on heating. Thermal processing of plant tissues alters the physical and chemical properties of plant cell wall and modifies fibre solubilization, which modifies the water extract viscosity (WEV). Our study had in view the effect of thermal processing on WEV of wheat flour.