Effect of extraction conditions on the solubility of non-starch polysaccharides ofwheat and barley

摘要

The main physicochemical properties of non-starch polysaccharides (NSP) that are of nutritional significance include hydration properties, viscosity, cation exchange capacity and absorptive properties of organic compounds. Almost all water-soluble polysaccharides produce viscous solutions. The viscous properties of NSP depend on several factors, including their chemical composition, molecular size and composition of the extraction media. Wheat and barley contain substantial amounts of both soluble and insoluble NSP. The predominant water-soluble NSP in wheat is arabinoxylan (6-8%), while (3-glucan is the predominant NSP in barley (7.6%). Experiments were conducted to investigate the influence of extraction conditions (pH and extraction time) on theviscosity of wheat and barley aqueous extracts. The extractions of soluble NSP were carried out in distilled water and in acidic buffer at three extraction times (15, 30 and 60 min) at 40°C. Water extract viscosity (WEV) and acid extract viscosity (AEV)values for barley were higher than for wheat, because of the presence of very high molecular weight P-glucans. A maximum increase in the solubilization of NSP in the flour samples was observed at 60 min extraction time. In all experiments AEV values were higher than WEV values, with a maximum at 60 min extraction time. The correlation between WEV and AEV was high (0.9507, P<0.05) for barley and moderate (0.8197, P<0.05) for wheat. Arabinoxylans are quite acid labile since their arabinose side chains can be cleaved by weak acids. Therefore, the acidic buffer is not suitable for grains containing arabinoxylans. The higher AEV for barley indicates either that acidic pH increased the extractability of P-glucans or prevented enzymatic hydrolysis of beta-glucans. The results demonstrated that the acid medium is more suitable for soluble NSP extraction from barley than from wheat.