Effect of soy residue (okara) on in vitro protein digestibility and oil release in high-calorie emulsion stabilized by heated mixed proteins

This study investigated the influences of a dietary fiber source – namely okara powder (OKP) and pectinase-hydrolyzed okara powder (PHO) – on the physicochemical characteristics of a high-calorie emulsion (1 kcal/mL) stabilized by sodium caseinate and soy protein isolate at a ratio of 0.7:0.3, with caloric distribution from carbohydrate:protein:lipid of 55:15:30. The viscosity and microstructure of the emulsion containing 0.08% (w/v) crude fiber and its digesta were monitored during in vitro protein digestion by pepsin and trypsin, along with the interfacial protein content in the cream phase, the soluble protein content in the serum phase, and oil release during the course of digestion. Use of OKP induced the formation of a thick paste under acidic conditions, and oil could be released after 15 min digestion by pepsin. On the other hand, the presence of PHO increased the viscosity of the emulsion under acidic pH to less extent than did the OKP and delayed the release of oil for up to 105 min during peptic digestion. The oil could be released from PHO-containing digesta after tryptic digestion, both in the absence and presence of bile acid. The study indicated that the rate of nutrient release can be controlled by the presence and type of dietary fiber source.