Preparation and characterization of emulsion gels stabilized by adequately preprocessed insoluble soybean fiber from okara

Abstract

Emulsion gels as soft materials were formulated by insoluble soybean fiber (ISF) assembled from okara in this study. Steam explosion on okara (ISF_S) transformed the insoluble fiber in the original okara (ISF_U) into soluble fiber. Enzymatic hydrolysis led to a lower protein content, smaller particle size and smaller contact angle of ISF. ISF_E, which was obtained by enzymatic hydrolysis of ISF_U, was not able to produce stable emulsion gels at 0.50 to 1.50 wt% ISF, whereas the ISF after a combined steam explosion-enzymatic hydrolysis treatment (giving rise to ISF_SE) stabilized emulsion gels at varying oil volume fractions (φ) from 10 to 50%. The ζ-potential of emulsion gels was around −19 to −26 mV. The droplet size first decreased (from 43.8 μm to 14.8 μm when at φ = 0.3) with increasing ISF content (from 0.25 wt% to 1.25 wt%) and then remained constant, as also seen from the microstructure. The apparent viscosity and viscoelastic properties were strengthened upon increasing both the ISF concentration and oil volume fraction. The protein and soluble fiber contributed to the interfacial activity of ISF while the insoluble fiber played an important role in the gel-like structured network of emulsion gels, making them maintain physical stability during long term storage. These findings could provide novel information about soybean fiber to fabricate soft materials and the utilization of okara at an industrial-scale.