Emulsifying properties of soy proteins: A critical review with emphasis on the role of conformational flexibility.

Soy proteins as important food ingredients exhibit a great potential to be widely applied in food formulations, due to their good nutrition, functional properties and health effects. The knowledge about the structure-function relationships of these proteins is crucial for their applications, but still very scant, especially that on their molecular mechanism of emulsification. The purpose of this review is to present a comprehensive summary of the knowledge about emulsifying and interfacial properties of soy proteins, achieved during the past decades, and particularly to provide an insight in understanding the role of conformational flexibility in their emulsifying properties. The interplays between the emulsifying and interfacial properties are also elucidated. For these proteins, the conformational flexibility rather than the surface hydrophobicity is the crucial parameter determining their emulsification performance. On the other hand, evidence is fast growing to indicate that because of the insoluble nature, soy proteins are a kind of unique materials to perform as food-grade Pickering stabilizers. The knowledge about the Pickering emulsion stabilization is distinctly different from that for conventional emulsions stabilized by soy proteins. Thus, different strategies should be employed to develop soy proteins into a kind of effective emulsifiers, depending on the preference of emulsification performance or emulsion stability.

Soy protein isolate as a nanocarrier for enhanced water dispersibility, stability and bioaccessibility of ß-carotene.

BACKGROUND: The incorporation of ß-carotene, one of the most common pigments or bioactives, into food formulations has attracted increasing interest from the food industry, due to its good nutrition and potential health effects. However, it is poorly soluble and unstable in water, which greatly limits its applications in foods. This work presented an effective approach to improve the water dispersibility, stability and even bioaccessibility of ß-carotene, using soy protein isolate (SPI) to perform as effective nanocarriers for this molecule. RESULTS: The complexation with SPI remarkably improved the water dispersibility and stability against heating and freeze-drying of ß-carotene. However, the encapsulation efficiency and stability of ß-carotene in the nanocomplexes with SPI were closely dependent on the applied ß-carotene-to-protein ratio, at which the complexation occurred. The best improvement of stability was observed at appropriate ß-carotene-to-protein ratios, e.g. 10-20 g kg-1 . The complexation with ß-carotene mainly occurred on the surface of SPI nanoparticles, through hydrophobic interactions. The complexation resulted in inter-particle aggregation, in a concentration-dependent manner. Almost all of the ß-carotene molecules in the nanocomplexes could be progressively released into the aqueous phase. CONCLUSION: SPI exhibits a good potential to perform as a nanocarrier for enhanced water dispersibility, stability and bioaccessibility of ß-carotene. © 2016 Society of Chemical Industry.

Influence of glycation on microencapsulating properties of soy protein isolate-lactose blends.

BACKGROUND: There is increasing interest in developing encapsulating materials from vegetable proteins as an abundant alternative for animal proteins or petroleum-derived polymers. Relationships between emulsifying and microencapsulating properties of soy protein isolate or blends with carbohydrates have not been well characterised. The influence of glycation between soy protein isolate and lactose prior to emulsification on the emulsifying and microencapsulation properties of their blends was investigated in this work. RESULTS: Analysis of the emulsion characteristics indicated that the glycation resulted in a decreased size of emulsion droplets, enhanced emulsion stability, and decreased apparent viscosity, suggesting improvement of emulsifying properties. In the spray-dried emulsions, the treatment with increasing degree of glycation from 0 to 13% progressively increased the retention efficiency from 96.4 to 98.3%. The glycation with an appropriate degree of glycation significantly decreased mean droplet size of the reconstituted emulsions, and increased the dissolution rate and capacity. However, the storage stability of the powders at 75% relative humidity was decreased by the glycation, though to a limited extent. CONCLUSION: Glycation improves the encapsulation efficiency, redispersion and dissolution properties of soy protein isolate-lactose blends, but slightly accelerated the storage instability of the spray-dried emulsions. The improvement of microencapsulation properties has been related to that of the emulsifying properties.

Heteroprotein complex between soy protein isolate and lysozyme: Protein conformation, lysozyme activity, and structural characterization.

Heteroprotein complexes are formed by electrostatic interactions of oppositely charged proteins in a purely aqueous environment. Understanding the relationship between their structural and functional properties will contribute to their tailor-made applications. Therefore, this study investigated the protein conformation, assembling structure, and enzyme activity of soy protein isolate/lysozyme (SPI/LYS) complexes at mass ratios of 2:1 (soluble complex) and 1:1.3 (stoichiometric ratio). Electrostatic complexation increased the surface hydrophobicity of complexes. Their surface hydrophobicity decreased with increasing NaCl concentrations and reached the theoretical values at the critical salt concentration of 200 mM NaCl. Electrostatic complexation did not decrease the LYS activity (∼43,000 units/mg). SPI/LYS complexes exhibited flocculated structures in which the two proteins were unevenly distributed; these were typical amorphous complexes. High dilution disassembled these complexes over 5 µm into particles of ∼100 nm, and NaCl reduced the size of these particles. Immobilized water was detected in the complexes formed by particle flocculation.

Freeze-thaw-stable high internal phase emulsions stabilized by soy protein isolate and chitosan complexes at pH 3.0 as promising mayonnaise replacers.

The development of cholesterol-free mayonnaise has attracted increasing interest in the food colloid field, due to the potential health concerns as a result of consumption of cholesterol-rich mayonnaise. One effective strategy in this regard is to substitute or partially substitute egg yolk with other organic emulsifiers and stabilizers, without affecting the quality of the product. In the work, we reported an effective strategy to fabricate high freeze-thaw-stability high internal phase emulsions (HIPEs), using complexes of a heated soy protein isolate (SPI) and chitosan (CS) at pH 3.0 as the emulsifiers and stabilizers. The SPI/CS complexes, formed even at a very low CS-to-SPI ratio, e.g., 1:10, showed a high capacity to stabilize HIPEs with a high freeze-thaw stability. Increasing the CS-to-SPI ratio in the complexes resulted in a progressive strengthening of gel network in the corresponding HIPEs, together with a gradual improvement of emulsification performance. The gel network of the HIPEs stabilized by the SPI/CS complexes was mainly maintained by the inter-droplet noncovalent interactions involving the CS molecules. The presence of CS also progressively increased the percentage of adsorbed proteins at the interface, and decreased the surface coverage of proteins at the interface. The high freeze-thaw stability of such HIPEs might be unrelated to the ice crystal formation during the freezing, and was more likely associated with the strong steric repulsion contributed to the adsorbed CS molecules between different droplets. The results indicated that the complexation of heated SPI and CS could provide an effective strategy to facilely fabricate outstanding freeze-thaw-stability HI PEs as potential mayonnaise replacers.

Physicochemical and structural characterisation of protein isolate, globulin and albumin from soapnut seeds (Sapindus mukorossi Gaertn.).

The amino acid (AA) composition and physicochemical and conformational properties of protein isolate (SNPI), globulin (SNG) and albumin (SNA) fractions from soapnut seeds were evaluated. The essential AA of SNG, SNA and SNPI (except sulfur-containing AA) are sufficient for the FAO/WHO suggested requirements for 2-5year old infants. SNG and SNPI showed similar electrophoresis patterns and AA compositions, the subunit of those proteins consisted of two polypeptides linked by disulfide bonds. In contrast, SNA showed a different AA compositions and SDS-PAGE pattern. Both SNG and SNPI presented a typical U-shape protein solubility (PS)-pH profile, SNA showed a completely different PS-pH profile, especially at pH 2.0-4.0. The near-UV circular dichroism (CD), differential scanning calorimetry (DSC) and tryptophan fluorescence spectra analyses indicated that the flexibility in tertiary conformations decreased in the order: SNA>SNPI>SNG, while soapnut proteins had a similar secondary conformation, with a highly ordered structure (the ß-types), as evidenced by far-UV CD spectra.

Conformational and thermal properties of phaseolin, the major storage protein of red kidney bean (Phaseolus vulgaris L.).

BACKGROUND: A previous study of various functional and physicochemical properties of phaseolin indicated good potential of phaseolin for application in food formulations in view of its excellent functional properties. The aim of the present study was to explore the conformational and thermal properties of phaseolin in the presence of protein structural perturbants by intrinsic fluorescence emission spectroscopy and differential scanning calorimetry. Raman spectroscopy was also used to characterise the secondary structures of phaseolin. RESULTS: The Raman spectrum of phaseolin indicated that ß-sheets and random coils were the major secondary structures. Intrinsic fluorescence emission spectroscopy confirmed the structural peculiarity and compactness of phaseolin, as evidenced by the absence of any shift in emission maximum (λ(max)) in the presence of structural perturbants such as sodium dodecyl sulfate (SDS), guanidine hydrochloride, urea and dithiothreitol (DTT). Increasing NaCl concentration enhanced the thermal stability of phaseolin. Addition of chaotropic salts (1 mol L(-1)) caused progressive decreases in thermal stability following the lyotropic series of anions. Decreases in thermal denaturation temperature (T(d)) and enthalpy change (ΔH) were observed in the presence of protein perturbants such as SDS, urea and ethylene glycol, indicating partial denaturation and a decrease in thermal stability. DTT and N-ethylmaleimide had little effect on the thermal properties of phaseolin, confirming that phaseolin, a 7S globulin, is devoid of inter-polypeptide disulfide bonds. CONCLUSION: The data presented here demonstrate the contributions of hydrophobic and electrostatic interactions and hydrogen bonding to the conformational stability of phaseolin.

Assembled milk protein nano-architectures as potential nanovehicles for nutraceuticals.

Nanoencapsulation of hydrophobic nutraceuticals with food ingredients has become one of topical research subjects in food science and pharmaceutical fields. To fabricate food protein-based nano-architectures as nanovehicles is one of effective strategies or approaches to improve water solubility, stability, bioavailability and bioactivities of poorly soluble or hydrophobic nutraceuticals. Milk proteins or their components exhibit a great potential to assemble or co-assemble with other components into a variety of nano-architectures (e.g., nano-micelles, nanocomplexes, nanogels, or nanoparticles) as potential nanovehicles for encapsulation and delivery of nutraceuticals. This article provides a comprehensive review about the state-of-art knowledge in utilizing milk proteins to assemble or co-assemble into a variety of nano-architectures as promising encapsulation and delivery nano-systems for hydrophobic nutraceuticals. First, a brief summary about composition, structure and physicochemical properties of milk proteins, especially caseins (or casein micelles) and whey proteins, is presented. Then, the disassembly and reassembly behavior of caseins or whey proteins into nano-architectures is critically reviewed. For caseins, casein micelles can be dissociated and further re-associated into novel micelles, through pH- or high hydrostatic pressure-mediated disassembly and reassembly strategy, or can be directly formed from caseinates through a reassembly process. In contrast, the assembly of whey protein into nano-architectures usually needs a structural unfolding and subsequent aggregation process, which can be induced by heating, enzymatic hydrolysis, high hydrostatic pressure and ethanol treatments. Third, the co-assembly of milk proteins with other components into nano-architectures is also summarized. Last, the potential and effectiveness of assembled milk protein nano-architectures, including reassembled casein micelles, thermally induced whey protein nano-aggregates, α-lactalbumin nanotubes or nanospheres, co-assembled milk protein-polysaccharide nanocomplexes or nanoparticles, as nanovehicles for nutraceuticals (especially those hydrophobic) are comprehensively reviewed. Due to the fact that milk proteins are an important part of diets for human nutrition and health, the review is of crucial importance not only for the development of novel milk protein-based functional foods enriched with hydrophobic nutraceuticals, but also for providing the newest knowledge in the utilization of food protein assembly behavior in the nanoencapsulation of nutraceuticals.

Nano-architectural assembly of soy proteins: A promising strategy to fabricate nutraceutical nanovehicles.

Use of protein-based nanovehicles has been well recognized to be one of the most effective strategies to improve water dispersibility, stability and bioavailability of nutraceuticals or bioactive ingredients. Thanks to their health-benefiting effects and unique assembly behavior, soy proteins seem to be the perfect food proteins for fabricating nanovehicles in this regard. This review presents the state-of-art knowledge about the assembly of soy proteins into nano-architectures, e. g., nanoparticles, nanocomplexes or nanogels, induced by different physicochemical strategies and approaches. The strategies to trigger the assembly of soy proteins into a variety of nano-architectures are highlighted and critically reviewed. Such strategies include heating, enzymatic hydrolysis, pH shift, urea or ethanol treatment, reduction, and static high pressure treatment. The self-assembly behavior of soy proteins (native or denatured) is also reviewed. Besides the assembly of proteins alone, soy proteins can co-assemble with polysaccharides to form versatile nano-architectures, through different processes, e.g., heating or ultrasonication. Finally, recent progress in the development of assembled soy protein nano-architectures as nanovehicles for hydrophobic nutraceuticals is briefly summarized. With the fast increasing health awareness for natural and safe functional foods, this review is of crucial relevance for providing an important strategy to develop a kind of novel soy protein-based functional foods with dual-function health effects from soy proteins and nutraceuticals.

Heteroprotein Complex Coacervate Based on ß-Conglycinin and Lysozyme: Dynamic Protein Exchange, Thermodynamic Mechanism, and Lysozyme Activity.

Heteroprotein complex coacervate (HPCC) is a liquid-like protein concentrate produced by liquid-liquid phase separation. We revealed the protein dynamic exchange and thermodynamic mechanism of ß-conglycinin/lysozyme coacervate, and clarified the effect of HPCC on protein structure and activity. ß-conglycinin and lysozyme assembled into coacervate at pH 5.75-6.5 and assembled into amorphous precipitates at higher pH. As the pH dropped from 8 to 6, the number of binding sites of the complex decreased in half, and the desolvation degree corresponding to the entropy gain was greatly reduced, conducing to the formation of coacervates rather than precipitates. The coacervates achieved the unique dynamic exchange by exchanging proteins with the diluted phase, making the uniform distribution of proteins in coacervates. The lysozyme activity was completely retained in ß-conglycinin/lysozyme coacervates. These results proved that ß-conglycinin-based heteroprotein complex coacervate is a feasible method to encapsulate and enrich active proteins in a purely aqueous environment.

Functional and conformational properties of phaseolin (Phaseolus vulgris L.) and kidney bean protein isolate: a comparative study.

BACKGROUND: Kidney bean (Phaseolus vulgris L.) seed is an underutilised plant protein source with good potential to be applied in the food industry. Phaseolin (also named G1 globulin) represents about 50 g kg(-1) of total storage protein in the seed. The aim of the present study was to characterise physicochemical, functional and conformational properties of phaseolin, and to compare these properties with those of kidney bean protein isolate (KPI). RESULTS: Compared with kidney bean protein isolate (KPI), the acid-extracted phaseolin-rich protein product (PRP) had much lower protein recovery of 320 g kg(-1) (dry weight basis) but higher phaseolin purity (over 950 g kg(-1)). PRP contained much lower sulfhydryl (SH) and disulfide bond contents than KPI. Differential scanning calorimetry analyses showed that the phaseolin in PRP was less denatured than in KPI. Thermal analyses in the presence or absence of dithiothreitol, in combination with SH and SS content analyses showed the contributions of SS to the thermal stability of KPI. The analyses of near-UV circular dichroism and intrinsic fluorescence spectra indicated more compacted tertiary conformation of the proteins in PRP than in KPI. PRP exhibited much better protein solubility, emulsifying activity index, and gel-forming ability than KPI. The relatively poor functional properties of KPI may be associated with protein denaturation/unfolding, with subsequent protein aggregation. CONCLUSION: The results presented here suggest the potential for acid-extracted PRP to be applied in food formulations, in view of its functional properties.

Heteroprotein complex coacervation: Focus on experimental strategies to investigate structure formation as a function of intrinsic and external physicochemical parameters for food applications.

Proteins are important components of foods, because they are one of the essential food groups, they have many functional properties that are very useful for modifying the physicochemical and textural properties of processed foods and possess many biological activities that are beneficial to human health. The process of heteroprotein complex coacervation (HPCC) combines two or more proteins through long-range coulombic interaction and specific short-range forces, creating a liquid-liquid colloid, with highly concentrated protein in the droplet phase and much more diluted-protein in the bulk phase. Coacervates possess novel, modifiable, physicochemical characteristics, and often exhibit the combined biological activities of the protein components, which makes them applicable to formulated foods and encapsulation carriers. This review discusses research progress in the field of HPCC in three parts: (1) the basic and innovative experimental methods and simulation tools for understanding the physicochemical behavior of these heteroprotein supramolecular architectures; (2) the influence of environmental factors (pH, mixing ratio, salts, temperature, and formation time) and intrinsic factors (protein modifications, metal-binding, charge anisotropy, and polypeptide designs) on HPCC; (3) the potential applications of HPCC materials, such as encapsulation of nutraceuticals, nanogels, emulsion stabilization, and protein separation. The wide diversity of possible combinations of proteins with different properties, endows HPCC materials with great potential for development into highly-innovation functional food ingredients.

Outstanding antioxidant pickering high internal phase emulsions by co-assembled polyphenol-soy ß-conglycinin nanoparticles.

This work reports a kind of novel antioxidant Pickering high internal phase emulsions (HIPEs; with an oil fraction, ϕ > 0.74) stabilized by soy ß-conglycinin (ß-CG) and polyphenol complex nanoparticles, as outstanding protective containers for lipophilic nutraceuticals. The nanoparticles with a representative polyphenol ((-)-epigallocatechin-3-gallate; EGCG) encapsulated were fabricated through an ethanol-mediated dissociation and re-assembly process of ß-CG, with greater particle size and higher surface hydrophilicity observed at higher initial EGCG concentrations. Using these co-assembled nanoparticles as sole stabilizers, a kind of HIPE gels with similar gel stiffness and microstructure, could be easily fabricated at ϕ = 0.8 and a protein concentration in the aqueous phase of 1.0 wt% using polyunsatuated fatty acid-rich flaxseed oil as the dispersed phase. These HIPE gels were extraordinarily stable against heating or long-term storage, but susceptible to freeze-thawing. The as-fabricated HIPEs showed an excellent protection to ß-carotene (encapsulated in oil phase) against heating, as well as an inhibition of lipid oxidation. The oxidation protection was in an EGCG concentration dependent manner. The results would be of interest for providing a novel strategy to fabricate functionalized Pickering HIPEs as potential containers or delivery systems for lipophilic nutraceuticals.

One-step fabrication of multifunctional high internal phase pickering emulsion gels solely stabilized by a softer globular protein nanoparticle: S-Ovalbumin.

A softer natural Pickering nanostabilizer, S-ovalbumin (S-OVA) was reported in this work, based on our previous researches about soft globular protein nanoparticles. Compared with native OVA, S-OVA has higher surface hydrophobicity, greater conformational flexibility and thinner tightly-bond water layer, which make it be unfolded more highly at the oil-water interface. However, S-OVA also possesses higher zeta-potential and thicker closely-surrounding water layer, offering it stronger electrostatic repulsion and steric hindrance between molecules and increased intramolecular cohesion. The improvements guarantee S-OVA undisintegrated particle structure and independent state on the interface and high refolding off the interface. The more flexible interior and firmer exterior together endow a higher softness to S-OVA. The HIPPE gels solely stabilized by S-OVA were fabricated using one-step shearing. These HIPPE gels own steady network structure mainly supported by bridging flocculation, strong self-supporting ability and moldability. The high storage stability and ability to inhibiting lipid oxidization provide the HIPPE gels an enormous potential in encapsulating and protecting volatile, easily-oxidized or dangerous organic liquids, during the storage and transportation. The attractive temperature responsiveness offers a high convenience to re-obtaining the organic liquids. And a re-encapsulation can be easily achieved via a re-shearing. The heat-enhanced gel intensity and moldability mean the HIPPE gels can be applied to produce dualistic gels or porous scaffolds with latent applications. These findings are helpful to explore more new Pickering stabilizers from the nature and extend the applications of HIPPEs in highly-demanded and high-tech industries.

Hofmeister Effect-Assistant Fabrication of All-Natural Protein-based Porous Materials Templated from Pickering Emulsions.

Porous materials derived from natural and biodegradable polymers have received growing interest. We demonstrate here an attractive method for the preparation of protein-based porous materials using emulsions stabilized by gliadin-chitosan hybrid particles (GCHPs) as the template, with the addition of gelatin and kosmotropic ions to improve the mechanical strength. The microstructure, mechanical properties, cytotoxicity, and fluid absorption behavior of porous materials were systematically investigated. This strategy facilitated the formation of porous materials with highly open and interconnected pore structure, which can be manipulated by altering the mass ratio of hexane or gelatin in the matrix. The Hofmeister effect resulted from kosmotropic ions greatly enhanced the Young's modulus and the compressive stress at 40% strain of porous materials from 0.56 to 6.84 MPa and 0.26 to 1.11 MPa, respectively. The developed all-natural porous materials were nontoxic to HaCaT cells; they also had excellent liquid (i.e., simulated body fluid and rabbit blood) absorption performance and advantages in resisting stress and maintaining geometry shape. The effects of different concentration amounts and type of salts in the Hofmeister series on the formation and performance of porous materials were also explored. Mechanical strength of porous materials was gradually enhanced when the (NH4)2SO4 concentration increased from 0 to 35 wt %, and the other four kosmotropic salts, including Na2S2O3, Na2CO3, NaH2PO4, and Na2SO4, also showed positive effects. This work opens a simple and feasible way to produce nontoxic and biodegradable porous materials with favorable mechanical strength and controllable pore structure. These materials have broad potential application in many fields involving biomedical and material science, such as cell culture, (bio)catalysis, and wound or bone defect healing.

[Effects of high pressure on the conformation of freeze-dried soy protein isolate: a FTIR spectroscopic study].

The effect of high pressure (HP)treatment on the conformation of freeze-dried soy protein isolates (SPI)was investigated by Fourier transform infrared (FTIR) spectroscopy. Within the amide I' region (1600-1700 cm(-1) of the deconvoluted FTIR curve of SPI, more than 10 bands associated with protein conformation were distinctly observed, attributed to the C==O stretching vibration and to a small extent to C--N stretching vibration of the peptide bonds, respectively. The secondary structure of native SPI is estimated to be composed of 15%-16% alpha-helix, 39%-44% extended strands, 17.5% random coils, and 21%-27% turns. The analyses of intensity and wavenumber of the bands showed that, HP treatment at pressures of 200-400 MPa resulted in the increases in intensity and a "red-shift" (about 2 cm(-1)) of these bands. HP treatment at 600 MPa further increased the band intensity of the amide I' region. The analyses of amide II bands showed that HP treatment led to gradual increases in intensity and absolute area of amide II bands, in a pressure-dependent manner. Thus, it is suggested that HP treatment resulted in gradual unfolding of secondary and tertiary structure of SPI, while the structure of denatured proteins underwent a "rebuilding" process after the release of high pressure. These results confirm that the HP-induced modification of SPI is by means of the HP-induced conformational changes.

Novel Soy ß-Conglycinin Core-Shell Nanoparticles As Outstanding Ecofriendly Nanocarriers for Curcumin.

The development of high-performance nanocarriers for nutraceuticals or drugs has become one of the topical research subjects in the functional food fields. In this work, we for the first time propose a novel and ecofriendly process to obtain a kind of nanostructured soy ß-conglycinin (ß-CG; a major soy storage globulin) as outstanding nanocarriers for poorly soluble bioactives (e.g., curcumin), by a urea-assisted disassembly and reassembly strategy. At urea concentrations > 4 M, the structure of ß-CG gradually dissociated into its separate subunits (α, α', and ß) and even denatured (depending on the type of subunits); after dialysis to remove urea, the dissociated subunits would reassemble into a kind of core-shell nanostructured particles, in which aggregated ß-subunits acted as the core while the shell layer was mainly composed of α- and α'-subunits. The core-shell nanoparticles were favorably formed at protein concentrations of 1.0-2.0 wt %. Curcumin crystals were directly introduced into the ß-CG solution at high urea concentrations (e.g., 8 M) and would preferentially interact with the denatured ß-subunits. As a consequence, almost all of the curcumin molecules were encapsulated in the core part of the reassembled core-shell nanoparticles. The loading amount of curcumin in these nanoparticles could reach 18 g of curcumin per 100 g of protein, which far exceeds those reported previously. The encapsulated curcumin exhibited a high water solubility, extraordinary thermal stability, and improved bioaccessibility, as well as a sustained release behavior. The findings provide a novel strategy to fabricate a kind of high-encapsulation-performance, organic solvent-free, and biocompatible nanocarrier for hydrophobic nutraceuticals and drugs.

Fabrication and Characterization of Novel Water-Insoluble Protein Porous Materials Derived from Pickering High Internal-Phase Emulsions Stabilized by Gliadin-Chitosan-Complex Particles.

Pickering high internal-phase emulsions (HIPEs) and porous materials derived from the Pickering HIPEs have received increased attention in various research fields. Nevertheless, nondegradable inorganic and synthetic stabilizers present toxicity risks, thus greatly limiting their wider applications. In this work, we successfully developed nontoxic porous materials through the Pickering HIPE-templating process without chemical reactions. The obtained porous materials exhibited appreciable absorption capacity to corn oil and reached the state of saturated absorption within 3 min. The Pickering HIPE templates were stabilized by gliadin-chitosan complex particles (GCCPs), in which the volume fraction of the dispersed phase (90%) was the highest of all reported food-grade-particle-stabilized Pickering HIPEs so far, further contributing to the interconnected pore structure and high porosity (>90%) of porous materials. The interfacial particle barrier (Pickering mechanism) and three-dimensional network formed by the GCCPs in the continuous phase play crucial roles in stabilization of HIPEs with viscoelastic and self-supporting attributes and also facilitate the development of porous materials with designed pore structure. These materials, with favorable biocompatibility and biodegradability, possess excellent application prospects in foods, pharmaceuticals, materials, environmental applications, and so on.

Functional properties and in vitro trypsin digestibility of red kidney bean (Phaseolus vulgaris L.) protein isolate: Effect of high-pressure treatment.

The effects of high-pressure (HP) treatment at 200-600MPa, prior to freeze-drying, on some functional properties and in vitro trypsin digestibility of vicilin-rich red kidney bean (Phaseolus vulgaris L.) protein isolate (KPI) were investigated. Surface hydrophobicity and free sulfhydryl (SH) and disulfide bond (SS) contents were also evaluated. HP treatment resulted in gradual unfolding of protein structure, as evidenced by gradual increases in fluorescence strength and SS formation from SH groups, and decrease in denaturation enthalpy change. The protein solubility of KPI was significantly improved at pressures of 400MPa or higher, possibly due to formation of soluble aggregate from insoluble precipitate. HP treatment at 200 and 400MPa significantly increased emulsifying activity index (EAI) and emulsion stability index (ESI); however, EAI was significantly decreased at 600MPa (relative to untreated KPI). The thermal stability of the vicilin component was not affected by HP treatment. Additionally, in vitro trypsin digestibility of KPI was decreased only at a pressure above 200MPa and for long incubation time (e.g., 120min). The data suggest that some physiochemical and functional properties of vicilin-rich kidney proteins can be improved by means of high-pressure treatment.

Ovalbumin as an Outstanding Pickering Nanostabilizer for High Internal Phase Emulsions.

There is still a debate about the effectiveness of native globular proteins to perform as Pickering-like stabilizers for oil-in-water high internal phase emulsions (HIPEs). In the work, we report one native globular protein (ovalbumin) with strong structural integrity and high refolding ability, exhibits an outstanding Pickering stabilization for HIPEs. Ultrastable gel-like HIPEs can be formed through a facile one-pot homogenization even at a concentration as low as 0.2 wt %. The HIPEs formed in the protein-poor regime are a kind of self-supporting and remoldable hydrogel consisting of bridging droplets. The formed HIPEs also exhibit other unique characteristics, such as extraordinary coalescence stability (against prolonged storage or heating), susceptibility to freeze-thawing, enhanced oxidation stability (to encapsulated bioactives), and inhibited vaporization of volatile oils. The findings would be of importance for extending the HIPEs to be applied in food, cosmetic, and petroleum industries.