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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.

Different pretreatments (homogenization, ultrasonic and steam-cooking treatments) before an alkaline extraction were employed to extract okara protein (OP) from defatted okara (residue left after extraction of the soy oil and water extractable fraction used to produce soybean protein isolates). The structure and functional properties of OPs subjected to pretreatments were determined. Analysis of fourier transform infrared spectroscopy (FTIR) revealed that the pretreatments had little effect on the secondary structure of OP. However, the tertiary structure of OP unfolded upon homogenization pretreatment and steam-cooking pretreatment, and the latter could lead to the increase in surface hydrophobicity (H0) of OP due to the exposure of hydrophobic groups resulted from partial unfolding, as demonstrated by fluorescence spectra. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) suggested that homogenization pretreatment and ultrasonic pretreatment did not destroy the subunit components of OP, but steam-cooking pretreatment could make OP denature and mostly degrade into small subunits because of higher temperature. Moreover, the changes in structure of OP significantly affected its functional properties. Results indicated that OP obtained by homogenization pretreatment exhibited the highest foaming ability index (FAI), while that of by ultrasonic pretreatment showed the highest foaming stability index (FSI), viscosity and emulsion stability. Steam-cooking pretreatment promoted the solubility and water holding capacity (WHC) of OP to the most extent. It should also be noticed that in comparison with commercial SPI, OP showed looser tertiary structure, higher H0 and similar SDS-PAGE pattern except for the detect of a glycoprotein, Bg 7S, which altogether resulted in better functional properties. In summary, OP has great potential to be applied in food area, especially in emulsifying agent and foam system.

Effect of xanthan gum (XG) on the walnut protein/xanthan gum mixtures (WP/XG, 1.2 wt% WP and 0–0.30 wt% XG), interfacial adsorption and emulsions properties was studied. As XG concentrations increased, the aqueous solutions of WP/XG mixtures were clear at pH 7.0 as shown by phase diagram, however, bigger hydrodynamic diameter (DH) and lower negative ζ-potential were observed which might be resulted from the formation of the co-solubilized WP/XG mixtures induced by electrostatic and hydrophobic interactions. As adsorption time prolonged, interfacial pressure (π), dilatational modulus (E), and dilatational elasticity (Ed) continuously increased, diffusion rate (kdiff) firstly increased and then decreased, inversely, penetration rate (kP), rearrangement rate (kR), dilatational viscosity (Ev) and loss-angle tangent (tanθ) decreased. These results indicated that XG promoted WP molecules to be continuously adsorbed to oil-water interface and formed firmer elastic interfacial films, possibly due to lower thermodynamic compatibility or higher viscosity. The oil droplets in emulsions stabilized by WP/XG mixtures had larger d4,3 and lower negative ζ-potential, and flocs were observed by CLSM images, which might be related to the adsorption of WP. Emulsions exhibited pseudo-plastic and shear-thinning properties by flow behavior measurements, and emulsions stability presented by creaming index (CI) was firstly decreased caused by flocs and then increased due to higher viscosity.

The physicochemical and interfacial properties of Okara protein (OP) are susceptible to be affected by various factors. In this respect, the role of inter- and intramolecular interactions between OP and carboxymethyl cellulose (CMC) were explored by in situ experiments. OP/CMC aqueous mixtures, containing 1.0 wt% OP and 0–0.5 wt% CMC, were prepared at pH 7.0 and 4.0. Subsequently, their physicochemical properties, interactions, and interfacial adsorption were comparatively characterized. OP formed larger aggregates at lower pH as confirmed by the visual appearance. The addition of CMC reduced the surface hydrophobicity and increased viscosity of OP/CMC mixtures regardless of pH. CMC increased the hydrodynamic diameter of mixtures at pH 7.0, while it led to more negatively-charged complexes with decreasing size at pH 4.0. Noticeably, the results regarding the interfacial pressure, adsorption kinetics and interfacial dilatational viscoelastic properties presented three remarkable phenomena: Low concentrations of CMC hardly affected the initial interfacial performance of OP at pH 7.0, whereas the latter was greatly reduced at high CMC concentrations. Moreover, high CMC concentrations appropriately reinforced the interfacial performance of OP at pH 4.0.

Cellulose derived from agricultural by-products as a promising stabilizer for novel food emulsions has been attracting numerous interests. In this work, defatted okara was used to extract insoluble soybean fiber (ISF) under alkaline pH (7.0–12.0). The physicochemical properties of ISF, as well as the formation and stability properties of O/W emulsions (10% w/w of oil) prepared by ISF, were characterized. The results exhibited a lower residual protein content (p

The physicochemical, interfacial and emulsifying properties of insoluble soy peptide aggregate (ISPA) modified by homogenization and alkaline-treatment (pH10, pH12) were studied in this paper. Homogenization and alkaline-treatment improved the content of hydrophobic amino acids of ISPA, promoting the surface hydrophobicity (H0), decreasing the hydrodynamic diameter (DH) and ζ-potential, finally enhanced the solubility and oil holding capacity (OHC). Compared to ISPA modified at pH10, ISPA modified at pH12 exhibited lower interfacial pressure (π) but higher viscoelastic modulus (E). Emulsions stabilized by modified ISPA had lower ζ-potential, smaller d4,3 and flocculation index (FI), and better stability than untreated ISPA. It was noticed that homogenization pretreatment had a synergistic effect with alkaline treatment on the improvement of emulsifying property. The effects of pH12 on the physicochemical properties of ISPA were more significant than pH10 possibly referred to the disrupting of intramolecular interaction, showing better solubility and emulsifying property. In summary, the emulsifying properties of modified ISPA were even better than that of commercial SPI, indicating that ISPA has the potential to be a good emulsifier in food industry.

A novel composite hydrogel incorporated physical-chemical treated insoluble (ISF) into high acyl gellan (HAG) was fabricated and characterized. ISF-HAG hydrogel exhibited better appearance and denser network structure compared to HAG hydrogel (control sample), which was further manifested by higher gel strength and storage module G′. It was attributed to hydrogen bonds between ISF and HAG, confirmed by FT-IR analysis, as well as ISF as a supporter or filler in the network pores. Temperature sweeps showed that the gel point temperature and gelling rate of ISF-HAG hydrogel were higher than those of control sample by a maximum of 5 °C and 5.22 Pa/°C, respectively. ISF-HAG hydrogel also presented good swelling capacity and texture properties. USAT-ISF obtained by ultrasonic assisted steam-cooking alkaline treatment exerted a great impact on the formation and performance of HAG hydrogel due to loose structure and outstanding physicochemical properties (water holding capacity, swelling capacity, etc.) This study explores the potential of ISF to promote gelation and expands the range of applications for HAG hydrogel.

Effects of insoluble soybean fiber (ISF) on the emulsion properties stabilized by soybean protein isolate (SPI, 0.40 wt%) and the stability of emulsions exposed to environmental conditions (pH and NaCl) were studied in this paper. As ISF increased (0–0.40 wt%), higher ζ-potential and smaller d4,3 of suspended SPI/ISF complexes were observed in aqueous system, which might be due to the interactions between SPI and ISF and the formation of SPI/ISF complexes. The ζ-potential of emulsions continuously decreased, the d4,3 firstly decreased and then increased while surface protein content (PA) and concentrations (Γ), viscosity as well as storage modulus (G′) continuously increased, which might be related to the low concentration of SPI, the SPI/ISF interactions and excessive unadsorbed ISF molecules in the continuous phase. The emulsions exhibited better resistance to pH and salt with increasing ISF while ISF also had a positive effect on the storage stability. All the results indicated that ISF could promote the stability of SPI emulsion, which was most likely ascribed to the electrostatic interactions, the gel-like network structure and the function of ISF as emulsifier and thickener, facilitating adsorption of protein onto the oil droplet surface and enhancing the interfacial protective coating. In summary, the ISF has a great potential to be applied in the emulsion system containing low-concentration protein, thus lowering the addition of protein and endowing the nutritional value of insoluble dietary fiber.