Extraction of water-soluble polysaccharides from kidney beans and examination of their protein dispersion and stabilization properties under acidic conditions

The extraction conditions of kidney bean water-soluble polysaccharides (SKPSs) from kidney bean fibers were examined. The factors such as temperature, pH, and time were combined to derive the conditions for obtaining high yields of high molecular mass polysaccharides. The optimal extraction temperature, time, and pH were 120 °C, 30 min, and 9, respectively. Under these conditions, the yield of SKPS (SKPS9) obtained was as high as 26.4%. The weight average molecular mass of SKPS9 measured using size exclusion chromatography equipped with a multi-angle laser light scattering detector was 2,530 kg/mole. The main constituent sugars of SKPS9 were arabinose (67.2%) and galacturonic acid (15.6%). SKPS9 carbohydrate molecules observed using a scanning probe microscope showed the mixed structures of a multi-branched structure, whose sugar chains extended outward from the center to the periphery of the molecule, and a little-branched straight chain structure. SKPS9 had protein dispersing and stabilizing properties under acidic conditions. In the acidified milk system containing 3% non-fat milk solids, 0.4% SKPS9 was able to maintain a mono-modal distribution of fine protein particles in pH level ranging from 3.8 to 4.4. This work suggests the potential for the creation of a value added ingredient from kidney bean.