Zhili Wan

Enhanced Physical and Oxidative Stabilities of Soy Protein-Based Emulsions by Incorporation of a Water-Soluble Stevioside–Resveratrol Complex

To strengthen the effectiveness of resveratrol (RES) as a natural antioxidant in food systems, this work attempted to enhance the water solubility of RES by utilizing the solubilizing properties of stevioside (STE) and investigated the effect of STE-solubilized RES (STE-RES) incorporation on the stability of soy protein isolate (SPI)-based emulsions. The physical properties and oxidative stability of SPI emulsions with STE/STE-RES were evaluated. The water solubility of RES increased with the increase of STE concentration up to its critical micelle concentration, suggesting the solubilization of hydrophobic RES in STE self-assembled micelles. STE micelles competitively adsorbed at the oil-water interface with SPI, forming a mixed SPI and STE interfacial layer, thus resulting in a decrease in particle size and evident enhancement in the physical stability of SPI-based emulsions. After the incorporation of STE-RES, SPI emulsions showed an enhanced oxidative stability with reduced lipid hydroperoxides and volatile hexanal. This improvement was believed to be mainly attributed to the targeted migration of RES to the interface during the adsorption of the STE-RES complex, as evidenced by high interfacial accumulation of RES.

Complexation of resveratrol with soy protein and its improvement on oxidative stability of corn oil/water emulsions

This work was to evaluate the potential of soy protein isolate (SPI)-resveratrol (RES) complex as an emulsifier to improve the effectiveness of RES as a natural antioxidant in corn oil-in-water emulsions. The physical properties and oxidative stability of emulsions stabilized by the native SPI-RES and heated SPI-RES complexes were evaluated. The water solubility of RES was enhanced by complexation with SPI, which was mainly driven by hydrophobic interactions. Heat treatment favoured the formation of the SPI-RES complex and endowed it with a higher antioxidant activity. Furthermore, the emulsions stabilized by the SPI-RES complexes showed an increased oxidative stability with reduced lipid hydroperoxides and volatile hexanal. This improving effect could be attributed to the targeted accumulation of RES at the oil-water interface accompanied by the adsorption of SPI, as evidenced by the high interfacial RES concentration. These findings show that the soy protein-polyphenol complex exhibited a good potential to act as an efficient emulsifier to improve the oxidative stability of emulsions.

Synergistic foaming and surface properties of a weakly interacting mixture of soy glycinin and biosurfactant stevioside.

The adsorption of the mixtures of soy glycinin (11S) with a biosurfactant stevioside (STE) at the air-water interface was studied to understand its relation with foaming properties. A combination of several techniques such as dynamic surface tension, dilatational rheology, fluorescence spectroscopy, and isothermal titration calorimetry (ITC) was used. In the presence of intermediate STE concentrations (0.25-0.5%), the weak binding of STE with 11S in bulk occurred by hydrophobic interactions, which could induce conformational changes of 11S, as evidenced by fluorescence and ITC. Accordingly, the strong synergy in reducing surface tension and the plateau in surface elasticity for mixed 11S-STE layers formed from the weakly interacting mixtures were clearly observed. This effect could be explained by the complexation with STE, which might facilitate the partial dissociation and further unfolding of 11S upon adsorption, thus enhancing the protein-protein and protein-STE interfacial interactions. These surface properties were positively reflected in foams produced by the weakly interacting system, which exhibited good foaming capacity and considerable stability probably due to better response to external stresses. However, at high STE concentrations (1-2%), as a consequence of the interface dominated by STE due to the preferential adsorption of STE molecules, the surface elasticity of layers dramatically decreased, and the resultant foams became less stable.

Formation of Complex Interface and Stability of Oil-in-Water (O/W) Emulsion Prepared by Soy Lipophilic Protein Nanoparticles

A lipophilic protein nanoparticle (LPP) was fabricated by ultrasonication of the soy lipophilic protein (LP), which contains hydrophobic proteins and phospholipids. This LPP (Rh = 136 ± 0.8 nm, ζ-potential = -20 mV, pH 7.0) had an improved dispersibility and acted as an emulsifier. The oil/water (O/W) emulsion stabilized by this LPP exhibited superior physical stability over long-term storage (8 weeks), during a stress storage test (200 mM NaCl addition and heating at 90 °C), and in the presence of Tween 20 (1.0-4.0 wt %), in contrast to those emulsions stabilized by β-conglycinin and glycinin. Langmuir-Blodgett method and interface pressure determination revealed that LPP formed rigid and rough granular film at air/water interface. The excellent stability of emulsions stabilized by LPP highlights the synergic effect between hydrophobic proteins and phospholipids. These findings suggest that the complexes of hydrophobic protein aggregates and biosurfactant could form a stable interface which could be developed into a novel strategy to fabricate a stable food emulsion.

Nonlinear Surface Dilatational Rheology and Foaming Behavior of Protein and Protein Fibrillar Aggregates in the Presence of Natural Surfactant

The surface and foaming properties of native soy glycinin (11S) and its heat-induced fibrillar aggregates, in the presence of natural surfactant steviol glycoside (STE), were investigated and compared at pH 7.0 to determine the impact of protein structure modification on protein-surfactant interfacial interactions. The adsorption at, and nonlinear dilatational rheological behavior of, the air-water interface were studied by combining drop shape analysis tensiometry, ellipsometry, and large-amplitude oscillatory dilatational rheology. Lissajous plots of surface pressure versus deformation were used to analyze the surface rheological response in terms of interfacial microstructure. The heat treatment generates a mixture of long fibrils and unconverted peptides. The presence of small peptides in 11S fibril samples resulted in a faster adsorption kinetics than that of native 11S. The addition of STE affected the adsorption of 11S significantly, whereas no apparent effect on the adsorption of the 11S fibril-peptide system was observed. The rheological response of interfaces stabilized by 11S-STE mixtures also differed significantly from the response for 11S fibril-peptide-STE mixtures. For 11S, the STE reduces the degree of strain hardening in extension and increases strain hardening in compression, suggesting the interfacial structure may change from a surface gel to a mixed phase of protein patches and STE domains. The foams generated from the mixtures displayed comparable foam stability to that of pure 11S. For 11S fibril-peptide mixtures STE only significantly affects the response in extension, where the degree of strain softening is decreased compared to the pure fibril-peptide system. The foam stability of the fibril-peptide system was significantly reduced by STE. These findings indicate that fibrillization of globular proteins could be a potential strategy to modify the complex surface and foaming behaviors of protein-surfactant mixtures.

Chitin Microfibers Reinforce Soy Protein Gels Cross-Linked by Transglutaminase

To improve the gel strength, we attempt to introduce the microcomposite concept into the food gel system. A stable positively charged chitin microfibers (CMFs) suspension was fabricated by a facile microfluidizer approach without changing its chemical structure. The obtained CMFs bearing width of about 0.5-5 μm and length of more than 500 μm were then developed in a transglutaminase cross-linked β-conglycinin (7S) gel. The morphological and rheological characterizations of the 7S-CMF composited gels were done as a function of the protein and CMFs concentrations. Results showed that the presence of the CMFs network improved the gel strength significantly. This effect was CMFs content dependent and was related to the formation of a sponge-like porous microstructure. We inferred that the CMFs provided an initial framework for gel formation and added structural rigidity to the protein gel. The role of protein was to participate in network development as an electrostatic coating and gelation component.

Contribution of Long Fibrils and Peptides to Surface and Foaming Behavior of Soy Protein Fibril System.

When soy glycinin (11S) is heated for a prolonged time at pH 2 (20 h at 85 °C), a mixture is formed consisting of long semiflexible 11S fibrils and small peptides. The surface and foaming properties of this mixture were investigated at different pHs, and compared to the behavior of pure fibrils and pure peptides, to determine the individual contributions of these two factions to the behavior of the mixture. The adsorption of these three systems at air-water interfaces and the resulting surface rheological properties were studied by combining drop shape analysis tensiometry, ellipsometry, and surface large amplitude oscillatory dilatational (LAOD) rheology. Lissajous plots of surface pressure versus deformation were used to analyze the surface rheological response in terms of interfacial microstructure. Our results show that the adsorption kinetics, dilatational rheological properties, and the foaming behavior of the mixture were mainly dominated by the small peptides in the fibril system. Compared to pH 2, the fibril mixture at pH 5 and 7 provides much better foam stability and appears to be a very promising protein material to make stable foams, even at low protein concentration (0.1 wt %). The presence of fibril clusters and peptide aggregates at pH 5 and 7 contributed to foam stability of the mixture. In contrast, pure fibril formed an interface with a highly pH-responsive adsorption and rheological behavior, and the foamability and foam stability of the pure fibrils were very poor.

Modulation of the surface properties of protein particles by a surfactant for stabilizing foams

In this study, a detailed investigation into the behavior of foams stabilized by mixtures of zein/TA colloidal particles (ZTP) with a conventional anion surfactant (sodium dodecyl sulfate, SDS) has been made. Foams stabilized by either particles or surfactants alone break down completely within one day at all concentrations tested in the present study. However, ZTP can be induced to form fractal clusters in the presence of a surfactant. In mixed particle–surfactant systems, a synergism occurs with respect to foam properties, since the fractal clusters can be used as building blocks with reaction activity to form stable foams with an orderly interfacial architecture. The formability of ZTP–SDS mixtures increases with the increase of SDS concentration. However, the foam stability increases to a maximum at 0.6 mM SDS followed by a decrease at higher SDS concentrations. In addition, the presence of SDS increases the surface tension decay rate and dilatational modulus, but it seems that their changes are not directly proportional to the SDS concentration. This study indicates that particle–surfactant mixtures can be a potential strategy to modify the particle surface properties and therefore improve foam properties, facilitating the application of zein-based particles in the food and cosmetic industry.

Fabrication and delivery properties of soy Kunitz trypsin inhibitor nanoparticles

Soy Kunitz trypsin inhibitor nanoparticles (KTIP) were prepared successfully by heating KTI at 80 °C in the presence of sodium sulfite. This treatment not only inactivated most trypsin inhibitor activity (TIA) of KTI (about 90.63%), but also resulting in the formation of KTI nanoparticles (about 85.92 nm) with good monodispersity (PDI: 0.18), which were confirmed by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) determination. SDS-PAGE analysis revealed that the formation of limited aggregates (KTIP) was mediated by an –SH/–SS– exchange reaction. The delivery capacity of KTIP for curcumin as model bioactives was evaluated. The results indicated that the co-assembly of KTIP and curcumin actually greatly enhanced the dispersibility, stability and bioaccessibility of curcumin in aqueous solution. Moreover, in vitro anti-proliferative activity on tumor cells assay showed that nanoparticulate curcumin was more effective than free curcumin in solution by controlling the tumor cell growth with time. These findings suggest that KTIP could be developed as a novel nano-delivery vehicle for hydrophobic bioactives and for use in functional foods and pharmaceutics.

The physicochemical properties, in vitro binding capacities and in vivo hypocholesterolemic activity of soluble dietary fiber extracted from soy hulls

Soluble dietary fibers (SDFs) have earned a healthy reputation due to their distinguished physiological functions. In this study, SDF was efficiently extracted from soy hulls using a phosphate-assisted subcritical water extraction method. The physicochemical properties, in vitro binding capacities and in vivo hypocholesterolemic activity of soy hull soluble dietary fiber (SHSDF) were evaluated. The results indicated that the major component of SHSDF was pectic polysaccharides, and with comparison to commercial oat β-glucan, SHSDF had favorable solubility, viscosity, water-holding ability (5.26 g water per g sample), and oil holding capacity (4.83 g oil per g sample). It also possessed good in vitro cholesterol-binding capacity (6.18 mg g-1 sample at pH 2 and 7.62 mg g-1 sample at pH 7), bile acid-binding capacity (3.3, 1.73 and 6.65 μM of GCA, GCDCA and GDCA per 100 mg of sample), glucose dialysis retardation index (64.76%), and in vivo hypocholesterolemic activity (16.88% and 35.28% reduction in serum total cholesterol and LDL level in rats, respectively). These data suggest that SHSDF has great potential in food applications, especially in the development of functional food ingredients.