Effect of soybean soluble polysaccharides on the stability of milk protein under acidic conditions

Soybean soluble polysaccharide (SSPS) extracted from soybean cotyledons has a pectin-like structure. SSPS has been used as a dispersion stabilizer for milk protein under acidic conditions, below the isoelectric point of milk protein, in a manner similar to high methoxyl pectin. SSPS at concentrations of less than 0.2% stabilized acidic beverages prepared with 8.0% of milk solid non-fat at pH 3.4–4.4, in contrast with pectin which needed at least 0.4% concentration. To elucidate the structure of the polysaccharide, which seemed likely to have a significant influence on its ability to stabilize acidic beverages, SSPS was digested with purified pectinases and hemicellulases, and the stabilizing effects of the digestion products on acidic beverages were analyzed. The stabilizing ability of SSPS was reduced by digestion of its neutral sugar side chains, arabinan or galactan, and was only slightly changed by digestion of its galacturonan main backbone with polygalacturonase or rhamnogalacturonase. This indicates that neutral sugar side chains, which mainly consist of arabinose and galactose residues, play a significant role in the ability of SSPS to stabilize acidic beverages. In contrast, the stabilizing effect of pectin was reduced by digestion of its galacturonan backbone, and was not changed by digestion of its neutral sugar side chains. This indicates that SSPS may differ from pectin in the mechanism by which it stabilizes milk proteins under acidic conditions.