Improvements in physicochemical and emulsifying properties of insoluble soybean fiber by physical-chemical treatments

Abstract

Initial structural, physicochemical and emulsifying properties of insoluble soybean fiber (ISF) obtained by alkaline treatment (AT), ultrasonic alkaline treatment (UAT), steam-cooking alkaline treatment (SAT), ultrasonic-assisted steam-cooking alkaline treatment (USAT) were investigated. The loose structure, porous and wrinkled surface was observed in ISF by scanning electron microscopy (SEM). USAT exerted a greatest influence on ISF micromorphology due to a strong combination of ultrasonic, steam-cooking and alkaline treatment. The rupture of polymer chains in ISF, which indicated release of free hydroxyl groups, was showed by Fourier transform infrared spectroscopy (FTIR) analysis. Water holding capacity (WHC), swelling capacity (SWC) and oil holding capacity (OHC) of USAT-ISF were increased to 3.84, 9.04 and 4.19 folds of NT-ISF, respectively. It was because loose and porous structure of ISF enhanced its ability to capture water or oil, and free hydroxyl groups acted as water holding sites as well. SAT-ISF and USAT-ISF suspensions showed more pronounced shear thinning behavior and higher apparent viscosity, which was related to WHC, SWC and cluster structure. Good dispersion of oil droplets was observed in fresh AT-ISF and UAT-ISF emulsions with little flocculation. AT-ISF emulsion presented a relatively high storage stability over 35 days as a function of broken sheet structure, moderate apparent viscosity and high WHC, OHC. It could be seen from dynamic viscoelastic measurements that SAT-ISF and USAT-ISF emulsions presented weak gel behavior. Results demonstrated that physicochemical and emulsifying properties of ISF were effectively improved by physical-chemical treatments, thus showing promising prospect of ISF as an emulsifier in food industry.