Emulsifying properties of enzyme-digested soybean soluble polysaccharide

Soybean soluble polysaccharide (SSPS), deriving from the by-product of the isolation of soybean protein, is known to stabilize oil-in-water emulsions. To better understand which fraction of the polysaccharide chain determines the functionality of SSPS on making and stabilizing emulsions, SSPS was digested by purified pectinases (polygalacturonase (PGase) and rhamnogalacturonase (RGase)) or hemicellulases (galactosidase (GPase) and arabinosidase (AFase)). The emulsifying properties of the digested fractions were then evaluated. Emulsions containing 20% soybean oil at pH 4.0 were stable to creaming for 30 days when RGase-treated SSPS was used as emulsifier. This enzymatic treatment improved the emulsifying properties of SSPS, as less SSPS was needed to obtain a stable emulsion under the same conditions. Enzymatic modifications with PGase, GPase or AFase reduced the emulsifying properties of the polysaccharide. The ability of the emulsions to remain stable after dilution of the parent emulsion to 0.1% oil disappeared when the galactan or arabinan chains of SSPS were removed. These results indicated that the neutral sugar chains of SSPS, consisting of β-galactan and α-arabinan, play a fundamental role in the stabilizing properties of SSPS at oil/water interfaces, causing steric repulsion between the oil droplets.