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There is still a debate about the influence of salts on the freeze-thaw stability of emulsions. In this research, the influence of the NaCl addition (before or after the emulsification; 100–500 mM) on the freeze-thaw stability of the Pickering emulsions stabilized by heat-induced soy protein isolate (SPI) nanoparticles, at a given protein concentration of 1.0% (w/v) and oil fraction of 0.4, was investigated. The addition of NaCl resulted in considerable changes in particle characteristics (including particle size, surface hydrophobicity and ζ -potential) of the SPI nanoparticles, with the extent of the changes varying with the applied ionic strength ( μ ). Despite the NaCl addition before or after the emulsification, the presence of NaCl remarkably improved the freeze-thaw stability against droplet coalescence and creaming of the emulsions, though the improvement was related to the applied μ . The improvement of the freeze-thaw stability would be largely attributed to the strengthening of the interfacial protein or protein nanoparticle films coating droplets, rather than the inhibition of ice crystal formation by the presence of NaCl. If the salt was introduced before the emulsification, a gel-like network might be formed in the corresponding emulsions, which would further provide an additional stabilization against the freeze-thaw treatment. Optimal freeze-thaw stability was observed in the presence of appropriate concentrations of NaCl (e.g., 100–200 mM). This is the first report to indicate the importance of the electrostatic screening to the improvement of the Pickering emulsions stabilized by charged particles. The findings would be of great importance for the formulation of food grade emulsions with excellent freeze-thaw stability.

The freeze-thaw stability of Pickering emulsions stabilized by (nano)particles from heated soy protein isolate (SPI) and whey protein (WP), was investigated and compared with those stabilized by unheated SPI (or WP) and sodium caseinate (NaCN). The stability was evaluated in terms of flocculation and coalescence degrees, and creaming index, as well as differential scanning calorimetry (DSC) characteristics. The emulsions exhibited different patterns of freeze-thaw stability, depending on the type of applied proteins, as well as the cycle number of freeze-thaw treatment. In general, the emulsions stabilized by heated SPI and WP exhibited much better freeze-thaw stability against coalescence and creaming, than those by unheated counterparts. The freeze-thaw stability against creaming of the heated SPI emulsion was even much better than that of the NaCN emulsion. The emulsions stabilized by SPI or WP, unheated or heated, showed poor freeze-thaw stability against flocculation. The differences in freeze-thaw stability between different emulsions could be explained in terms of the differences in physicochemical parameters of proteins or protein particles, as well as their microstructure. The good freeze-thaw stability of the emulsions by heated SPI and WP might be largely due to the action of Pickering steric stabilization, while the gel-like network formation also attributed to the stability. The results would be of great importance for the fabrication of Pickering emulsions stabilized by food protein particles and their applications in food formulations.

Native potato starch (PS) granules were separated into three size fractions: larger than 30 μm (P-L), 15–30 μm (P-M), and smaller than 15 μm (P-S). The morphological and crystalline structure of fractionated potato starches were investigated by light and scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The P-L fraction showed ellipsoidal shape and B-type X-ray pattern, whereas the P-S fraction had spherical shape and A-type pattern. The fluorophore-assisted capillary electrophoresis data showed that the P-L fraction had more B2 chains and less short A and B1 chains than the P-S counterparts. Smaller granules with larger specific surface area had higher degree of substitution when reacted with octenylsuccinic anhydride (OSA), and showed more uniform distribution of octenylsuccinate substituents. Both OSA modified and unmodified P-S samples showed higher flowability compared with the P-L counterparts.

The development of food-grade Pickering stabilizers has recently attracted growing interests, due to their potential applications in food and pharmaceutical formulations. We report that glycinin (SG), one of major globulins in soy proteins, exhibits a very promising potential to perform as a kind of novel food-grade Pickering stabilizers for oil-in-water emulsions. The unheated SG at pH 7.0 was mainly present in the nanoparticle form (with a z-average diameter of 57 nm), and the heating at 90 or 100 °C considerably increased the particle size and surface hydrophobicity (by 5–6 fold) of the nanoparticles. The heating also remarkably changed the pattern of intra-particle interactive forces, and for the heated SG nanoparticles, their internal structure was mainly maintained by both hydrophobic interactions and disulfide bonds. The heating greatly improved the emulsification performance of the nanoparticles, especially at high concentrations (e.g. > 0.5%, w/v), as well as the stability of the corresponding emulsions against coalescence and creaming. As compared with the SG preparation heated at 90 °C, that at 100 °C exhibited a higher effectiveness to pack at the interface. The better emulsification performance for the heated SG preparations was closely associated with their more efficient packing and higher diffusion (or initial adsorption) at the interface. The results indicated that SG nanoparticles, unheated or heated, could be applied as a kind of Pickering stabilizers for oil-in-water emulsions; as compared to the unheated SG, the heated SG nanoparticles exhibited much better interfacial and emulsifying properties, thus imparting a better Pickering stabilization for the emulsions.

In recent years, there is increasing interest in the development of food-grade Pickering emulsions as promising delivery systems for bioactive compounds. Our previous work reported that most of the proteins in pea protein isolate (PPI) at pH 3.0, present in the nanoparticle form, can effectively perform as a kind of food-grade Pickering stabilizers for oil-in-water emulsions (LWT, 2014). The purpose of this study was to further report that PPI-stabilized emulsions at pH 3.0 exhibited great potential to act as intestine-targeted and sustained-release delivery systems for β -carotene. The emulsions were produced by microfluidization at a specific protein concentration of 6.0% (w/v) and varying oil fractions ( ϕ ) of 0.2–0.6. The results indicated that increasing ϕ was favorable for the gel-like network strengthening of these emulsions. The gel formation was largely related to the droplet flocculation as well as inter-floc attractive interactions. The in vitro simulated digestion results showed that the release of β -carotene during the intestinal digestion of these emulsions could be well modulated by altering ϕ . The gel-like emulsion at ϕ = 0.6 exhibited much lower release of β -carotene, but higher stability towards degradation during the digestion, than that at ϕ = 0.3. The findings provide important information not only for the design of novel delivery systems for lipophilic bioactive components, but also for the development of plant protein-based formulations.

The improvement of the freeze-thaw stability of emulsions by interfacial engineering has attracted increasing attention in recent years. The present work investigated the potential of using soy protein isolate (SPI) aggregate nanoparticles as the Pickering stabilizers to improve the freeze-thaw stability of the resultant emulsions. SPI nanoparticles with different particle sizes and surface properties were fabricated through heating the SPI solutions (at a constant protein concentration of 2%, w/v) at 95 °C for 15 min, by varying the ionic strength (I) in the range of 0-500 mM. The nanoparticles fabricated at I values of 100-500 mM exhibited larger particle sizes and higher surface hydrophobicity, but poorer emulsification efficiency than those at I = 0.05 mM. The presence of NaCl during the nanoparticle fabrication resulted in the formation of a kind of gel-like emulsion with a high extent of droplet flocculation. The emulsion stabilized by SPI nanoparticles at I = 0.05 mM was highly susceptible to coalescence, flocculation and creaming upon freeze-thaw treatment, while those in the presence of NaCl exhibited excellent freeze-thaw stability. The much better freeze-thaw stability of the emulsions in the presence of NaCl (relative to that at I = 0.05 mM) was largely attributed to the gel-like network formation, rather than the salt itself. The results indicated that a kind of Pickering emulsion with excellent freeze-thaw stability, stabilized by heat-induced SPI nanoparticles, could be fabricated by heating the SPI solutions at I values of 100-500 mM. The findings would be of great relevance for providing important information about the development of food grade Pickering emulsions stabilized by protein-based particles, with potential applications in frozen food, or functional food formulations.

In this paper we reported that pea protein isolate (PPI) at pH 3.0 exhibits a novel Pickering stabilization for oil-in-water emulsions. At pH 3.0, most of the proteins in PPI were present in the nanoparticle form, with the hydrodynamic diameter of 134–165 nm depending on the concentration (c; 0.25–3.0 g/100 mL). For the emulsions formed at a specific oil fraction of 0.2, increasing the c from 0.25 to 3.0 g/100 mL resulted in a considerable reduction in the emulsion size, while their creaming stability progressively increased, and especially at c values higher than 2 g/100 mL, no creaming occurred even after storage of 20 days. Confocal laser scanning microscopy observations showed that increasing the c resulted in a progressive increase in extent of droplet flocculation, and at higher c values, a network consisting of flocculated droplets could be formed. The emulsions formed at c values above 1.0 g/100 mL exhibited extraordinary stability against coalescence. The flocculated droplet network formation was closely associated with the increased amount of adsorbed proteins at the interface. The results suggest that pea proteins exhibit a good potential to act as a kind of Pickering stabilizers for oil-in-water emulsions at acidic pHs.

Some physicochemical characteristics, microstructure and stability of native and preheated (95 °C, 15 min) soy protein isolate (SPI)-stabilized emulsions, formed at varying protein concentrations (c; 0.5–4.0%, w/v) in the absence or presence of 300 mM NaCl, were characterized. The emulsifying ability, flocculated state of droplets, microstructure, interfacial protein concentration (Γ) of the fresh emulsions, as well as stability of these emulsions against coalescence, flocculation, creaming and even lipid oxidation upon storage up to 2 weeks were evaluated. In general, increasing c was favorable for the emulsification efficiency, but the flocculated state of oil droplets or size of the flocs in the fresh emulsions was more affected by the presence of salt, and/or the heat pretreatment. Increasing ionic strength or application of a heat pretreatment resulted in remarkable increases in extents of droplet flocculation in the fresh emulsions, as well as amount and concentrat,ion of adsorbed proteins at the interface. All the emulsions exhibited an extraordinary stability against coalescence and/or flocculation. Increasing c led to a progressive increase in stability against creaming, especially for the preheated SPI emulsions with 300 mM NaCl. All the emulsions at c = 1% or above exhibited a similarly high oxidative stability upon storage up to 9 days. Even at c = 0.5%, the oxidative stability of the formed emulsions could be greatly improved by increasing ionic strength, and/or application of a heat pretreatment. The findings have important implications for the development of an important kind of protein-stabilized emulsions with industrial relevance.

Water-insoluble phytosterols were developed into a kind of colloidal particle as Pickering stabilizers for emulsions by a classic anti-solvent method using 100% ethanol as the organic phase to solubilize the phytosterols and whey protein concentrate (WPC) as the emulsifier. The colloidal particles in the dispersion, with morphology of stacked platelet-like sheets, had a mean diameter of 44.7 and 24.7 μm for the volume- and surface-averaged sizes, respectively. The properties and stability of the emulsions stabilized by these colloidal particles were highly dependent upon the applied total solid concentration (c; in the dispersion) and oil fraction (ø). The results indicated that (1) at a low c value (1.0%, w/v) the emulsions were susceptible to phase separation, even at a low ø of 0.2, (2) at low ø values (e.g., 0.2 or 0.3) and a relatively high c value (1.0%, w/v, or above), a severe droplet flocculation occurred for the emulsions, and (3) when both c and ø were appropriately high, a kind of self-supporting gel-like emulsions could be formed. More interestingly, a phase inversion of the emulsions from the oil-in-water to water-in-oil type was observed, upon the ø increasing from 0.2 to 0.6 (especially at high c values, e.g., 3.0%, w/v). The elaborated Pickering emulsions stabilized by the phytosterol colloidal particles with a gel-like behavior would provide a candidate to act as a novel delivery system for active ingredients.

The emulsifying and interfacial properties of vicilins from three selected Phaseolus legumes (kidney, red and mung beans; denoted as KV, RV and MV, respectively) at protein concentrations ( c ) of 0.25–2.5% (w/v) were investigated. The results indicated that the emulsifying ability and emulsion stability (against flocculation, coalescence and even creaming) of vicilins considerably varied with their type and c . In general, KV exhibited much better emulsifying ability than RV or MV. Increasing c basically facilitated formation of the fresh emulsions with less flocculated oil droplets, and enhanced their stability against coalescence. Increasing c progressively decreased the stability of KV and RV emulsions against flocculation and creaming, while in the MV case, least stability was observed at c = 1.0%. Besides the differences in conformational characteristics, the differences in emulsifying properties of these vicilins could be to a certain extent attributed to the differences in their interfacial properties, including ζ -potential and interfacial protein concentration, as well as unfolding, penetration and structural rearrangement at the interface. The findings are of great importance for extending the current knowledge about the emulsifying properties of vicilins, thus providing valuable information for the development of vegetable protein-stabilized emulsion products.

This study utilized a facile and continuous technique termed Flash NanoPrecipitation (FNP) to produce zein colloidal particles (ZP) without or with sodium caseinate (NaCas) as the stabilizer. The colloidal particle preparations were performed through a self-made Confined Impinge Jet (CIJ) mixer, and compared with traditional antisolvent processes. The influences of FNP processing parameters on the size of zein colloid particles, including flow rates, outlet configurations, solute concentrations and ethanol concentrations, were extensively discussed. The influences of viscous properties, buffering capacity and self-assembly of zein or NaCas on particle size and size distributions were also discussed. Particle sizes of ZP produced by the FNP technique are below 350 nm, even at high zein concentrations (2.5–7.5% w/v). Solvent systems with different ethanol concentrations yielded zein colloid particles with similar size, showing an attractive feature for industrial applications and encapsulating actives with different solubility in ethanol–water binary solvent. This study opens a promising pathway for continuously producing ZP via the FNP procedure.

Emulsifying properties of two partially purified legumin and vicilin (PL and PV) and protein isolate (PPI) from dry pea seeds at various pH values (3.0, 5.0, 7.0 and 9.0) were investigated. The tested emulsion characteristics included droplet size, flocculation and coalescence indices (FI and CI), creaming index, as well as interfacial protein adsorption. Some physicochemical properties of these proteins, e.g., free sulfhydryl and disulfide bond contents, protein solubility (PS), surface hydrophobicity (Ho) and thermal stability (and denaturation), were also characterized. The results indicated that emulsifying ability and emulsion stability of various pea proteins considerably varied with the preparation process, protein composition and pH. Overall, all the pea proteins exhibited least emulsifying ability at pH 5.0 (around isoelectric point), and concomitantly, the resultant emulsions were most unstable against coalescence and creaming. The emulsifying ability of these proteins at pH 3.0 was generally better than that at neutral or alkali pH values, and among all the three proteins, PL exhibited highest emulsifying ability at this pH. The flocculated state and size of droplets in fresh emulsions did not directly affect stability of these emulsions against flocculation and coalescence (upon 24 h of storage), and even creaming (up to 7 days). Interestingly, the PL and PV exhibited much better creaming stability than PPI, at pH deviating from the pI. The emulsifying properties of these proteins were not only related to their PS and Ho , but also associated with the protein adsorption and nature (e.g., viscoelasticity) of interfacial protein films. These results can greatly extend the knowledge for understanding the emulsifying properties of pea proteins, especially the pH dependence of emulsion characteristics.

A novel process to efficiently form soy protein isolate (SPI)-stabilized emulsion gels, induced by microbial transglutaminase (MTGase) was reported, with the enzyme added before the emulsification (instead of after the emulsification in the conventional case). The rheological behavior and microstructure of the formed emulsion gels (at a constant protein concentration of 6 g/100 mL and oil fractions (o) of 0.2–0.6) were characterized using dynamic oscillatory measurement and confocal laser scanning microscope. The gel stiffness of the formed gels with the novel process progressively increased with increasing enzyme concentration (1.0–5.0 U/g), or with the o increasing from 0.2 to 0.6. Interestingly, the gel stiffness at a given o with the novel process was considerably greater than that with the conventional process, though the enzyme concentration was less (e.g., 1.0 vs 20 U/g). Furthermore, a pre-incubation (15–60 min) of the proteins with the enzyme (before the emulsification) greatly improved the gelation. The analyses of droplet size and amount of entrapped proteins within the gel matrix indicated that during the initial gel network, the bridging flocculation of oil droplets played a prominent role, but the full development of the gel stiffness mainly depended on the inter-droplet covalent cross-linking.

Properties and storage stability of spray-dried emulsions stabilized by unheated and preheated (95 °C, 15 min) soy protein isolates, alone or in combination with lactose, were investigated. In general, the heat pretreatment greatly improved retention efficiency (RE), redispersion behavior, glass transition temperature ( T g ) and thermal stability of the emulsion powders, but accelerated instability of the reconstituted emulsions. Additional blending with lactose further considerably improved the RE and dissolution behavior, but significantly decreased the stability of reconstituted emulsions and T g . Storage at 75% relative humidity resulted in considerably increased droplet size of reconstituted emulsions, as well as decreased RE, wettability and T g , especially in the powders containing lactose. Microscopic observations confirmed that the changes in properties and stability of the powders upon storage were closely related to rupture of particle structure, and/or particle agglomeration. These findings provide fundamental understanding for the development of microencapsulated products using soy proteins as the wall materials.

The microencapsulating properties of soy protein isolate (SPI) by spray-drying, as affected by pressure level of homogenization, inlet air temperature of drying, core/wall ratio, as well as total solid content were evaluated. The test characteristics included retention efficiency (RE), redispersion behavior (droplet size distribution and mean size of reconstituted emulsions) of spray-dried powders, moisture content, dissolution behavior, and microstructure of particles. The influence of storage at 75% relative humidity for 7 days on these characteristics was also investigated. The results indicated that the RE, redispersion and/or dissolution behaviors, as well as storage stability of spray-dried emulsions were affected by various test parameters, but to a various extent. Among all test parameters, the core/wall ratio was the most pronounced one affecting the properties of the powders, regardless of after storage or not. In general, the RE of the dry powders was higher at increased pressure level, decreased core/wall material, as well as enhanced total solid contents; at a constant total solid content, the redispersion behavior of these powders was closely associated with their RE. At the core/wall ratios of 1:1 or higher, the storage resulted in remarkable decreases in RE of the powders, and impaired redispersion behaviors, while the powder at 1:2 core/wall ratio exhibited an excellent storage stability. Scanning electron microscopy observations confirmed that the differences in RE or storage stability at various core/wall ratios were related to the differences in their particle microstructure. These results would be of great help to understand the microencapsulation properties of SPI, thus providing some valuable information for the development of microencapsulated products using soy proteins as the wall materials.

The development of cold-set protein-stabilized emulsion gels has attracted increasing interests, due to their potential to be applied as a kind of release-controlled carriers, especially for labile lipid-soluble bioactive compounds. This work aimed to elucidate the importance of changing oil volume fraction (o = 0.2–0.6) for the formation and properties of cold-set soy protein isolate (SPI)-stabilized emulsion gels, induced by microbial transglutaminase (MTGase). The gelation process, mechanical properties, water-holding capacity (WHC) and microstructure of the correspondingly formed gels at various o values were evaluated. The results indicated that increasing o progressively increased the storage modulus (gel strength) and WHC, from about 200 to 8000 Pa and 52 to 88%, respectively. The high o dependence of the gel strength and WHC was closely related to the microstructure of the formed gels. The network of the emulsion gels at high o values (e.g. 0.6) was particulate in nature with coarse strands mainly composed of compact ‘aggregated’ oil droplets, while that at low o values was filamentous or fine-stranded with oil droplets incorporated. The enzymatic treatment resulted in a progressive increase in amount of the proteins entrapped within the network, with highest extent observed at o = 0.5. The entrapped proteins involved the biopolymers of β -conglycinin subunits or glycinin acidic polypeptides, covalently cross-linked by the enzyme, together with glycinin basic polypeptides. The gelling mechanism at high o values could be largely related to aggregation or coagulation of protein-coated oil droplets, while that at low o values, the gels was more like enzyme-set protein gels. These results would be of great help for the understanding of the gelling mechanism and the development of enzyme-set protein-stabilized emulsion gels.

The kidney bean protein isolate-chitosan (KPI/CH) composite films were fabricated at acidic pH to design potential carriers for antimicrobials (e.g., nisin). Tensile and thermo-mechanical properties, surface hydrophobicity and surface free energy (γ) as well as microstructure of the composite films were evaluated. A peelable and self-supported film was obtained for the KPI alone, exhibiting the typical stiff behavior. In contrast, the complex between KPI and CH produced less rigid and much more flexible films, with decreased elastic modulus (EM), storage modulus (E′) and glass transition temperature (Tg). The inclusion of CH enhanced surface hydrophobicity of the films. Concomitantly, the surface free energy (γ) of the films exhibited a reduced tendency. Upon increasing CH-to-KPI ratios, the microstructures of the films changed gradually from protein continuous to bi-continuous, CH continuous pattern. Moreover, the KPI/CH blend films exhibited a visible compositional gradient, reflecting that the CH was rich in near-surface of the films, especially air side. Antimicrobial activity of the films was also analyzed, indicating the test bacteria, Bacillus subtilis, Escherichia coli and Salmonella were sensitive to KPI/CH composite films, in a CH-to-KPI dependent manner. The results presented here supported that the KPI/CH blend films are expected to serve as antimicrobial packaging for food or the carrier of antimicrobials (e.g., nisin).

Soy protein-stabilized emulsions or emulsion gels have recently attracted increasing interests in the research of food science. However, the importance of protein composition on the properties and microstructure of the formed emulsion gels is little understood. This paper investigated the influence of varying glycinin/β-conglycinin ratio on the properties, microstructure and gelling mechanism of soy globulin-stabilized emulsion gels, at a constant total protein concentration and oil fraction (6%, w/v, and 0.3), induced by microbial transglutaminase (MTGase; 20 U per gram of protein). The enzyme incubation resulted in the gelation of all soy globulin-stabilized emulsions, but the rheological properties, water holding capacity (WHC) and microstructure of the formed emulsion gels considerably varied with glycinin content in the globulin mixtures. Basically, increasing the glycinin content progressively increased the gel stiffness, but significantly decreased the WHC. Confocal laser scanning microscopic observations showed that increasing glycinin content led to the formation of emulsion gel network with a more inhomogenous and porous microstructure. The improvement of the gel stiffness by increasing glycinin content was largely associated with the enhanced flocculation of oil droplets, more proteins entrapped within the network, as well as more importance of covalent cross-links for the gel network at higher glycinin contents. The results confirmed that the properties of MTGase-set soy protein-stabilized emulsion gels can be well modulated by varying the protein composition. The findings are of important relevance for the development of cold-set soy protein-stabilized emulsion gels with targeted properties in the food or other fields.

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. © 2013 Society of Chemical Industry

The work reports the influence of stirring (with intermittent or continuous modes) during incubation on the rheological properties, water-holding capacity (WHC) and microstructure of soy protein isolate (SPI)-stabilized emulsion gels, induced by microbial transglutaminase (MTGase), at a constant protein concentration (6 g/100 mL) and three oil fractions (0.2, 0.4 and 0.6). The results indicated that the stirring simultaneously during incubation with the enzyme greatly facilitated the gel network formation and increased stiffness of the formed emulsion gels. The improvement of gel stiffness and WHC for the stirred-type gels was much better with the intermittent than continuous mode. The differences in rheological properties and WHC between different emulsion gels were basically consistent with the differences in their microstructure. Interestingly, the pattern of interaction forces involved in the gel network varied between unstirred and stirred gels, and even between the two stirring modes. The results suggest that the application of shearing could greatly improve the enzyme-induced gelation of protein-stabilized emulsions, and produce stirred-type emulsion gels with better water-holding and rheological properties, within a much shorter periods (relative to enzyme-set gels).

The complexation between soy soluble polysaccharide (SSPS) and curcumin at pH 7.0 and 4.0, as well as some physicochemical characteristics of the resultant complexes, was investigated. The encapsulation efficiency and loading amount of curcumin in the complexes at pH 4.0 reached 67.3% and 4.49 μg/mg SSPS, respectively. Ethanol-induced denaturation and structural unfolding of the protein fraction in SSPS was essential for complex formation. The complexation with curcumin resulted in aggregation of SSPS and the subsequent formation of compacted nanoparticles with curcumin as the core. The complexation greatly improved the heat stability and in vitro bioaccessibility of curcumin. In general, the encapsulation efficiency, heat stability, and bioaccessibility of curcumin in the complexes at pH 4.0 were better than those at pH 7.0. The findings are of importance for the development of food grade nanovehicles for enhanced water solubility, stability, and bioaccessibility of hydrophobic bioactives.

In this paper we reported the rheological and microstructural properties of a kind of novel cold, gel-like soy protein isolate (SPI) emulsions obtained by means of microfluidization. These gel-like emulsions were formed from untreated and preheated (95 °C, 15 min) SPI at a protein concentration of 6% (w/v), and various oil volume fractions (Φ; 0.2–0.6) and NaCl concentrations (0–500 mM). The rheological properties and microstructure were characterized using steady viscosity and dynamic oscillatory measurements, as well as confocal laser scanning microscopy (CLSM). The characteristics (e.g. droplet size distribution and creaming stability) of the emulsions, formed at lower protein concentrations (e.g. 0.5–4.0%), were also characterized, aiming to reveal the mechanism of the gel-like network formation. The dynamic oscillatory data indicated that both untreated and preheated SPI emulsions exhibited gel-like rheological properties, but the specific apparent viscosity (η) and storage modulus (G′) of the latter ones were much higher at a comparable Φ. Both η and G′ progressively increased upon Φ increasing, indicating enhanced inter-droplet interactions. At a given Φ value (0.3), increasing NaCl concentration progressively increased η and G′ of the preheated SPI emulsions, indicating the importance of electrostatic screening for the gel-like network formation. The CLSM analyses confirmed formation of the gel-like network, mainly composed of aggregated oil droplets, which was closely dependent on the Φ and NaCl concentration. The gel-like network was formed by bridging flocculation of oil droplets, mainly through inter-droplet hydrophobic interactions between the proteins adsorbed at the interface. These results suggested that soy proteins exhibit excellent potential to produce cold, gel-like emulsions, especially through a heat pretreatment followed by microfluidization, which might be of vital importance for the development of soy protein-based formulations, especially as carriers for heat-labile ingredients with health effects.

The development of food-grade (nano)particles as a delivery system for poorly water soluble bioactives has recently attracted increasing attention. This work is an attempt to fabricate food protein-based nanoparticles as delivery systems for improving the water dispersion and bioaccessibility of phytosterols (PS) by an emulsification–evaporation method. The fabricated PS nanoparticles were characterized in terms of particle size, encapsulation efficiency (EE%) and loading amount (LA), and ξ-potential. Among all the test proteins, including soy protein isolate (SPI), whey protein concentrate (WPC) and sodium caseinate (SC), SC was confirmed to be the most suitable protein for the PS nano-formulation. Besides the type of protein, the particle size, EE% and LA of PS in the nanoparticles varied with the applied protein concentration in the aqueous phase and organic volume fraction. The freeze-dried PS nanoparticles with SC exhibited good water re-dispersion behavior and low crystallinity of PS. The LA of PS in the nanoparticles decreased upon storage, especially at high temperatures (e.g., >25 °C). The PS in the fabricated nanoparticles exhibited much better bioaccessibility than free PS. The findings would be of relevance for the fabrication of food-grade colloidal phytosterols, with great potential to be applied in functional food formulations.

Gelatin/olive oil composite films were prepared through microfluidic emulsification technique in order to reduce the water affinity of protein-based film. The effects of oil content on lipid droplet distributions in the film-forming dispersions and emulsified films were evaluated and compared. The possible relationship between some selected physical properties and microstructure (e.g., lipid droplet size) of the films was also discussed. The volume-surface (D3,2) and weight (D4,3) mean diameters of lipid droplets in film-forming dispersion showed a reduced trend upon increasing oil amounts, whereas the lipid droplets in the films showed a different trend, i.e., first increase and then decrease. The water barrier capability and tensile strength (TS) showed an enhanced trend as the lipid droplets in the films decreased. In addition, the emulsified films exhibited excellent barrier ability to ultraviolet light, and the inclusion of olive oil enhanced the hydrophobic character of gelatin films. These results revealed that olive oil has a good potential to be incorporated into gelatin to make edible film or coating for some food applications.

Modifications in physicochemical, conformational and emulsifying properties of unheated and preheated soy protein isolates (SPIs) by microfluidization at a specific pressure level (120 MPa) were investigated. The heat pretreatment was carried out at temperatures of 75, 85 and 95 °C, respectively. The tested properties included protein solubility (PS), surface hydrophobicity (Ho), free sulfhydryl group (SH) and disulfide bond (SS) contents, conformational characteristics, as well as emulsifying properties (e.g. emulsifying ability index (EAI), particle size of oil droplets in the emulsions, creaming index). The results indicated that the microfluidization treatment generally increased PS, Ho, SS content, as well as EAI of both unheated and preheated SPIs, in a preheating temperature dependent way; the treatment also resulted in partial unfolding and denaturation, and even structural re-arrangement of the proteins; the treatment improved the emulsifying efficiency and stability against creaming, but accelerated the bridging flocculation of oil droplets in the preheated-SPI-stabilized emulsions, with higher extent of flocculation observed at higher temperatures of the pretreatment. Size exclusion chromatography and SDS-PAGE analyses confirmed that the microfluidization led to transformation of insoluble aggregates into soluble ones, in which SH/SS interchanges might be involved. The findings suggest that the microfluidization treatment, or in combination with a thermal pretreatment, would be an effective technique to improve surface properties of SPI.

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 2–5 year 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 β-types), as evidenced by far-UV CD spectra.

Novel cold, gel-like whey protein concentrate (WPC) emulsions at various oil fractions ( φ ; 0.2–0.6) were formed through thermal pretreatment (at 70 °C for 30 min) and subsequent microfluidisation. The rheogical properties and microstructures, as well as emulsification mechanism of these emulsions were characterised. The rheological analyses indicated that the gel-like emulsions exhibited shear-thinning and predominantly elastic gel behaviours, and the apparent viscosities and the mechanical moduli of the emulsions remarkably and progressively increased with increasing the φ from 0.2 to 0.6. Confocal laser scanning microscopy analyses confirmed close relationships between rheological properties and gel network structures at various φ values. The formation of the gel-like network structure was closely related to the high emulsifying efficiency by microfluidisation. This kind of novel gel-like emulsion might exhibit great potential and be applicable in food formulations, e.g. as a kind of carrier for heat-labile and active ingredients.

The effects of high hydrostatic pressure (HHP) treatment (100-500 MPa) on solubility and structural properties of ethanol (EtOH)-denatured soy β-conglycinin and glycinin were investigated using differential scanning calorimetry, Fourier transform infrared and ultraviolet spectroscopy. HHP treatment above 200 MPa, especially at neutral and alkaline pH as well as low ionic strength, significantly improved the solubility of denatured soy proteins. Structural rearrangements of denatured β-conglycinin subjected to high pressure were confirmed, as evidenced by the increase in enthalpy value (ΔH) and the formation of the ordered supramolecular structure with stronger intramolecular hydrogen bond. HHP treatment (200-400 MPa) caused an increase in surface hydrophobicity (F(max)) of β-conglycinin, partially attributable to the exposure of the Tyr and Phe residues, whereas higher pressure (500 MPa) induced the decrease in F(max) due to hydrophobic rearrangements. The Trp residues in β-conglycinin gradually transferred into a hydrophobic environment, which might further support the finding of structural rearrangements. In contrast, increasing pressure induced the progressive unfolding of denatured glycinin, accompanied by the movement of the Tyr and Phe residues to the molecular surface of protein. These results suggested that EtOH-denatured β-conglycinin and glycinin were involved in different pathways of structural changes during HHP treatment.

The mechanism of soy protein fractionation was explored. A Focused Beam Reflectance Measurement (FBRM) technique was used to study the effects of Ca2+ and Mg2+ concentrations on the aggregation/precipitation processes of soy globulins. An electrophoretic technique was used to provide information about the electrical charge of the resulting individual protein precipitate. FBRM measurements demonstrated the presence of a two-step process for glycinin (around 90% purity) aggregation. First, in the absence of Ca2+ and Mg2+, about 9730 counts of the primary particles (~ 3.33 μm) per second were formed immediately, with the pH being adjusted to 5.8 for glycinin precipitation. Second, more than 90% of the primary particles aggregated slowly within approximately 15 min into larger secondary particles (~ 54.72 μm). The addition of Ca2+ and Mg2+ significantly increased the amount of the primary aggregate of soy globulins and altered their aggregation process. However, the number of primary particles induced by Ca2+ was smaller than that by Mg2+. The aggregation kinetic pattern for soy globulins in the second precipitation step (mainly β-conglycinin) significantly differed from that of the first precipitation step (mainly glycinin) in the stability of secondary particles. Electrophoretic measurements showed that, as Ca2+ and Mg2+ concentrations were increased, the net ζ-potential of the glycinin-rich fractions decreased, and the reduced effect by using Ca2+ was greater than that by using Mg2+. The different influences on the ζ-potential for soy protein between Ca2+ and Mg2+ were probably due to their different influences on phytate precipitation, respectively. The combined effects of Ca2+ and Mg2+ and phytate led to the reduction in the ζ-potential and thus to colloidal stability for soy globulins, resulting in more protein precipitation.

Summary The aim of this investigation was to explore the pH-induced conformational changes of phaseolin using differential scanning calorimetry (DSC), fluorescence and circular dichroism (CD) spectra. The surface charges at the varying pH and ionic strength were also determined to probe the possible relationship between the surface charges of phaseolin and its conformation. The ζ-potential of phaseolin decreased from 27.9 mV at pH 3.0 to –44 mV at pH 9.4, and the isoelectric point (iep) occurred at pH 4.21, which were comparable with the theoretical estimations derived from amino acid composition and pK values. The iep of phaseolin was independent of ionic strength, while the magnitude of ζ-potential decreased as the ionic strength increased. The near-UV CD, DSC and fluorescence spectra analyses indicated highly acidic and alkaline pH conditions induced the loss of tertiary conformation of phaseolin. The far-UV CD spectra analysis confirmed pH-shift led to the decreases in ordered secondary structure compositions. The present results suggested the loss of secondary and/or tertiary conformation of phaseolin as a result of the varying pattern in electrostatic interactions as pH shifted from 7.0 to acidic or alkalic pH.

Summary The effect of pHs and heating on the protein–polysaccharide complexation between the 0.5 wt% soy globulin (7S or 11S) and 0.1 wt% chitosan was studied. Electrophoretic and light scattering techniques were used to examine the electrical charge and aggregation of the individual biopolymers and complexes. At pH 3.0–6.5, 7S (or 11S) globulin in the presence of chitosan had significantly higher ζ-potentials and lower particles size than 7S (or 11S) globulin alone did (e.g. 600–6000 nm at pH 5.5), indicating the formation of complexes. After heating 7S (or 11S)–chitosan mixtures had higher positive value of ζ-potential. 7S (or 11S)–chitosan mixtures exhibited a significant increase in positive value of ζ-potential and stability after heating at lower pH values (pH 3.3 instead of pH 4.5). Compared with other mixtures, at pH 2.5–6.0, the most remarkable decrease in aggregation was obtained for 11S–chitosan mixtures after heating at pH 3.3.

Red bean 7S globulins (vicilins) with different polypeptide constituents or heterogeneity were fractionated using acidic extraction (at 0.5 M NaCl) and anion-exchange column chromatography. The physicochemical and conformational properties, including amino acid composition, net charge and/or surface hydrophobicity ( H 0 ), protein solubility (PS), thermal and emulsifying properties, as well as secondary, tertiary and/or quaternary conformations, were evaluated. There were distinct differences in zeta potential, H 0 , DSC characteristics, emulsifying activities and tertiary and/or quaternary conformations among the vicilins with different polypeptide constituents, but the PS and secondary conformation were slightly different. The PS as a function of pH and thermal stability were closely related to their surface charge and/or hydrophobicity. The emulsifying ability and the emulsion stability were closely dependent on the PS and H 0 , and even the flexibility in tertiary and/or quaternary conformations. These results suggested good relationships between the physicochemical functions and conformational features of red bean vicilins, which could be of great help for further utilization of legume proteins as a potential functional ingredient.

Steady shear and dynamic oscillatory measurements were used to investigate the effect of concentration, ionic strength and thermal treatment on rheological properties of soybean β-conglycinin in aqueous dispersions. SDS-PAGE and Differential Scanning Calorimetry (DSC) showed that β-conglycinin exhibited partial denaturation and formation of aggregates during isolation. Under steady shear flow, strong shear-thinning behavior was observed with increasing shear rate from 0.001 to 1200 s−1. A dispersion of β-conglycinin (≥5% w/v, without applying thermal treatment) exhibited gel-like dynamic mechanical spectra at 20°C. This suggested that β-conglycinin in aqueous dispersions showed rheological properties of typical weak gel-like (entanglement) or semi diluted polymeric solution. Weak gel network of β-conglycinin was susceptible to ionic strength, suggesting that electrostatic forces play an important role in the formation of weak gel network. These properties of β-conglycinin have practical significance for t...

The effects of succinylation at three anhydride levels (0.2, 0.4, and 0.6 g g−1) on the properties of cast films from red bean protein isolate (RPI) at three glycerol levels of 0.2, 0.4, and 0.6 g g−1 were investigated. The tested properties included tensile strength (TS) and elongation at break (EB), surface hydrophobicity, moisture content (MC), total soluble matter (TSM), water vapor transmission rate, and permeability (WVTR and WVP), permeability coefficient of oil (PO). The results showed that the succinylation greatly improved the mechanical properties (especially the EB), but decreased the surface hydrophobicity of cast films. The MC, TSM, WVTR, WVP, and PO were considerably increased by the succinylation. The size exclusion chromatography analysis indicated that the succinylation resulted in protein aggregation or association, and transformation of insoluble precipitates (initially present) to soluble protein components. The dependence of the influence of succinylation upon some selected properties on the plasticizer level suggests interactions between introduced anionic succinic moieties and the hydroxyl groups of the plasticizer. These results suggest that the succinylation treatment could be applied to modify the mechanical properties of legume proteins, especially in the case that requires excellent flexibility of cast films. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Fluorescence and differential scanning calorimetry (DSC) were used to study changes in the conformation of red kidney bean (Phaseolus vulgaris L.) protein isolate (KPI) under various environmental conditions. The possible relationship between fluorescence data and DSC characteristics was also discussed. Tryptophan fluorescence and fluorescence quenching analyses indicated that the tryptophan residues in KPI, exhibiting multiple fluorophores with different accessibilities to acrylamide, are largely buried in the hydrophobic core of the protein matrix, with positively charged side chains close to at least some of the tryptophan residues. GdnHCl was more effective than urea and SDS in denaturing KPI. SDS and urea caused variable red shifts, 2-5 nm, in the emission λ(max), suggesting the conformational compactness of KPI. The result was further supported by DSC characteristics that a discernible endothermic peak was still detected up to 8 M urea or 30 mM SDS, also evidenced by the absence of any shift in emission maximum (λ(max)) at different pH conditions. Marked decreases in T(d) and enthalpy (ΔH) were observed at extreme alkaline and/or acidic pH, whereas the presence of NaCl resulted in higher T(d) and ΔH, along with greater cooperativity of the transition. Decreases in T(d) and ΔH were observed in the presence of protein perturbants, for example, SDS and urea, indicating partial denaturation and decrease in thermal stability. Dithiothreitol and N-ethylmaleimide have a slight effect on the thermal properties of KPI. Interestingly, a close linear relationship between the T(d) (or ΔH) and the λ(max) was observed for KPI in the presence of 0-6 M urea.

This study aimed at establishing an effective preparative isolation method of soy β-conglycinin constituent subunits and characterizing some of their physicochemical properties and their heat-induced aggregation. These subunits were isolated in relatively large amounts and in high purity by dissociating β-conglycinin in 6 M urea and using a combination of DEAE-Sepharose fast flow column chromatography and immobilized metal ion affinity chromatography (IMAC). At a pH deviating from isoelectric point (pI), zeta potentials of α′ and α subunits were much larger than that of β subunit, while in the latter case, the hydrophobic groups were more buried within the proteins. Dynamic light scattering analysis indicated that the extent of heat-induced aggregation of β subunit was much higher than that of α′ and α subunits, and the aggregation was also more affected by the increase in ionic strength. Atomic force microscopy analysis indicated that more ordered and stranded aggregates were formed for α′ and α subunits. These results confirm a close relationship between physicochemical properties and heat-induced aggregation of β-conglycinin subunits.

A simple two step precipitation method was used to investigate the effect of MgCl 2 instead of CaCl 2 on fractionation of soybean glycinin and β-conglycinin. Compositional and physicochemical properties of the resulting protein fractions were characterised. The optimised procedure, in terms of protein yield, purity, phytate content and physicochemical properties, was obtained when the addition of 5 mM MgCl 2 was used. After application of 5 mM MgCl 2 , the phytate content of the glycinin-rich and β-conglycinin-rich fractions was about 0.4% and 1.3%, respectively, but the addition of 5 mM CaCl 2 increased the phytate content of the glycinin-rich fraction to 1.25% and decreased that of β-conglycinin-rich fraction to 0.67%. Low phytate protein product was suitable for use in infant formula and acidic food. The solubility of the glycinin-rich fractions with MgCl 2 was significantly higher than that with CaCl 2 at pH < 4.5. Application of MgCl 2 improved thermal stability of the β-conglycinin-rich fraction.

The effects of succinylation and acetylation on some functional, structural properties and in vitro trypsin digestibility of hemp protein isolate (HPI) were investigated. The extent of acylation gradually increased from 0 to 60―70%, with the anhydride-to-protein ratio increasing from 0 to 1.0 g g ―1 . Size exclusion chromatography showed that succinylation led to formation of more soluble protein aggregate than acetylation, especially at anhydride levels higher than 0.1 g g ―1 . Succinylation led to gradual increase in protein solubility (PS) from 30 to 85―90%, while in the acetylation case, the PS was improved only at low anhydride levels, increasing from 30 to about 50% with anhydride-to-protein ratio increasing from 0 to 0.2 g g ―1 . At neutral pH, the emulsifying activity indexes (EAI) of HPI was 22.1 m 2 g ―1 , and the EAI linearly and significantly increased with the extent of acylation. The EAIs of succinylated and acetylated HPI (1.0 g g ―1 ) were 119.0 and 54.4 m 2 g ―1 , respectively. Differential scanning calorimetry (DSC) and intrinsic fluorescence spectrum analyses indicated gradual structural unfolding of proteins, or exposure of hydrophobic clusters to the solvent, especially at higher anhydride levels. Additionally, the in vitro trypsin digestibility was significantly improved by the succinylation. The results indicated that the chemical acylation treatment (especially succinylation) could be applied to modify some selected functional properties of hemp proteins, especially PS and emulsifying ability.

The amino acid composition, some selected physicochemical and functional properties of acidic and basic polypeptides of soy glycinin were investigated and compared. Large amount of these polypeptides were obtained by DEAE-Sepharose fast flow column chromatography. Free sulphydryl contents, surface hydrophobicity, solubility and emulsifying activities (at different pH values) were evaluated. Different polypeptides had different patterns of amino acid composition, especially contents of acidic (and basic) and hydrophobic amino acids. The free sulphydryl contents (including total and exposed) and surface hydrophobicity considerably varied with the type of polypeptides. Compared with glycinin, isoelectric point (pI) of individual polypeptides shifted towards a more acidic pH. At a given pH value (e.g. above or below pI), the solubility and emulsifying ability index of these polypeptides were closely related to their relative contents of acidic (and basic) amino acids. The results indicated that glycinin polypeptides with different amino acid character have different physicochemical and functional properties, especially solubility and emulsifying ability.

The formation of soluble aggregates from insoluble precipitates of commercial soy protein isolate (SPI) by means of combined homogenization and ultrasonic treatment was characterized. The heat-induced gelation of formed soluble aggregates was also investigated. The turbidity and electrophoresis analyses showed that initially insoluble precipitates of commercial SPI, most basic subunits of glycinin included, were transformed into soluble aggregates. High performance size exclusion chromatography (HPSEC) analysis confirmed the formation of soluble aggregates. Both non-covalent and covalent interactions, e.g. hydrophobic interactions, hydrogen bonds and disulfide bonds, were involved in the formation of soluble aggregates. The formation of soluble aggregates remarkably improved the heat-induced gelling ability of commercial SPI.

Enzymatic hydrolysis of hemp protein isolate (HPI) by six proteases (alcalase, flavourzyme, neutrase, protamex, pepsin and trypsin) and antioxidant activities of the resulting hydrolysates, obtained for 2 and 4 h were investigated. The yield of trichloroacetic acid (TCA)-soluble peptides (Ysp), protein composition and surface hydrophobicity (Ho) of the hydrolysates were evaluated. The results showed that the hydrolysates exhibited varying DPPH radical scavenging (with lowest IC50, ∼2.3 mg/mL) and Fe2++ chelating (with lowest IC50 of 1.6–1.7 mg/mL) abilities and reducing power (with highest absorbance at 700 nm of 0.31–0.35), depending on their Ysp and Ho values. The DPPH radical scavenging and Fe2++ chelating abilities of the hydrolysates were positively correlated with their Ysp or Ho values. The results suggest that enzymatic hydrolysis can be used as an effective technique to produce high value-added products of hemp proteins.

The aggregation and structural properties of soy protein isolate (SPI), induced by high pressure (HP) treatment at 200–600 MPa were investigated by size-exclusion chromatography combined with multi-angle laser scattering (SEC-MALLS) and fourier transform infrared (FTIR) spectroscopy. HP treatment at lower pressure level (e.g., 200 MPa) resulted in formation of marked insoluble aggregate of SPI, while the treatment at higher pressure level (e.g., 600 MPa) led to transformation of insoluble aggregate to soluble one. The soluble aggregate formed at 400 or 600 MPa had much less mean molecular weight (MW) (about 5.2 × 10 6 g/mol) than that at 200 MPa (about 1.6 × 10 7 g/mol), and was also much more homogenous in MW distribution. FTIR analyses confirmed changes in secondary and tertiary structures, induced by HP treatment. These results can provide direct evidence or explanation for HP-induced modification of soy proteins.

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.

The effects of high-pressure (HP) treatment on some physicochemical and functional properties of soy protein isolates (SPI) were investigated. Surface hydrophobicity (Ho), free sulfhydryl (SH) content, differential scanning calorimetry characteristics, protein solubility, emulsifying activities, and heat-induced gelling property were evaluated. HP treatment at 200–600 MPa resulted in a slight but gradual decline in solubility, and a significant (P

Effects of limited enzymatic hydrolysis induced by trypsin on the physicochemical and functional properties of hemp (Cannabis sativa L.) protein isolate (HPI) were investigated. The enzymatic hydrolysis was confirmed by sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and size exclusion chromatography (SEC). SEC and differential scanning calorimetry (DSC) analyses confirmed the presence of aggregates in the corresponding hydrolysates (with the degree of hydrolysis of 2.3–6.7%). Functional properties, including protein solubility (PS), thermal properties, emulsifying and foaming properties, and water holding and fat adsorption capacities (WHC and FAC) were evaluated. The PS was remarkably improved by the limited enzymatic hydrolysis at all tested pH values. However, the enzymatic hydrolysis led to the marked decreases in emulsifying activity index, foaming capacity and foam stability, WHC and FAC. These decreases were to a great extent related to the presence of aggregates in the hydrolysates.

Soluble soybean protein aggregate (SSPA) was efficiently prepared from alcohol-washed insoluble soybean protein concentrate (SPC) by the method of hydrothermal cooking (HTC) with high pressure homogenization and evaluated by differential scanning calorimetry (DSC), SDS-PAGE, gel filtration chromatography and texture analyzer. The conditions of low ionic strength and low concentration of protein (

The effect of processing on some functional properties and in vitro digestibility of buckwheat protein products (BWP) was investigated. In the spray-dried cases, the protein solubility (PS) of BWP was much greater than that of commercial soy protein isolates (SPI) at below pH 5 and above pH 6 (P < 0.05). At below pH 7, the PS of those BWPs by ultrasonic-assisted extraction was higher than that by mechanical extraction or by ultrasonic-assisted extraction and additional de-fatting treatment. The water holding capacity of those BWPs obtained by freeze-drying was also significantly higher than that by spray-drying (P < 0.05). The fat adsorption capacity of freeze-dried BWPs was significantly higher than that of SPI and those spray-dried BWPs (P < 0.05). The emulsifying activity index (EAI) of some spray-dried BWPs was higher than that of SPI at below pH 4 and above pH 6, while the emulsion stability index (ESI) was lower than that of SPI at below pH 7 (P < 0.05). The de-fatting pretreatment could improve the EAI and ESI of BWP, especially at above pH 6. In simulated gastric fluid, the digestion pattern of BWP was evidently different from that of SPI. In the pepsin digestion, the % N release was affected by the processing. The BWPs with low lipid contents had higher % N release as compared to those with high lipid contents. These results suggested that the functional properties and in vitro digestibility of BWP be associated with its lipid and ash contents, which could be affected by processing. Thus, functional and nutritional BWPs, potential for food applications, can be produced through controlling the processing.

The effects of processing parameters, including the applied amount of microbial transglutaminase (MTGase), the pH of film-forming solution, air-drying temperature, as well as the additional pre-incubation, on the properties of MTGase-treated soy protein isolate (SPI) films were investigated. The treatment with low concentration of MTGase (4–10 units per gram of SPI, U g− 1) significantly increased the tensile strength (TS) values of SPI films, while high concentration of MTGase (over 20 U g− 1) resulted in significant decrease in the TS values (P ≤ 0.05). The elongation at break (EB) values of corresponding films gradually decreased, and the contact angle values persistently increased with the enzyme concentration. At alkaline pH range, the TS and EB values of MTGase-treated SPI films were significantly higher than that at pH 7.0 (P ≤ 0.05). Meanwhile, the contact angle values significantly decreased with increasing pH from 7.0 to 10.0 (P ≤ 0.05). The TS, EB and contact angle values of MTGase-treated films gradually but insignificantly decreased with increasing the air-drying temperature from 18 to 50 °C (P > 0.05). The properties of MTGase-treated films were also affected by the additional pre-incubation of film-forming solutions with MTGase before casting. Furthermore, the aggregation of SPI or its components induced by MTGase has been proved to mainly account for the influence of processing parameters on the properties of SPI films (MTGase-treated). Thus, low concentration of enzyme, alkaline pH range and low air-drying temperature, at which conditions the MTGase-induced aggregation of SPI in film-forming solutions could be in some extent inhibited or delayed, might facilitate the improvement of the properties of SPI films by MTGase, especially the mechanical and surface hydrophobic properties. Industrial relevance The development of biodegradable protein film has attracted a lot of attention worldwide. The enzymatic cross-linking induced by transglutaminase has been confirmed to improve mechanical and surface hydrophobic properties of cast films from most of food proteins, including soy proteins. Results of this study show that, the improvement of properties of cast films of soy proteins by transglutaminase treatment is largely dependent upon many processing parameters, e.g., enzyme concentration, the pH of film-forming solution and temperature.

The effects of microbial transglutaminase (MTGase) treatment on the mechanical and hydrophobic properties of cast films from various food proteins were investigated. SDS-PAGE analyses confirmed that the MTGase treatment led to the formation of insoluble film network for most of food proteins. This enzymatic treatment significantly (P < 0.05) increased tensile strength (TS) values of cast films of all food proteins by 13-33% (except whey proteins). Meanwhile, the influence on the elongation at break (EB) values was mainly dependent upon the molecular nature of proteins. For most of food proteins, both increases in TS and EB values of films were obtained after the MTGase treatment. Furthermore, the surface hydrophobicity of most of protein films was also significantly improved. These results suggest that the enzymatic treatment by MTGase could be used as an effective technique to improve mechanical and surface hydrophobic properties of protein films.

The thermal properties of buckwheat proteins (BP) as related to their lipid contents were studied using differential scanning calorimetry (DSC). BP samples with three levels of lipid content (2.5%, 6.5% and 17.8%, w/v) were obtained by selecting different extraction and de-fatting techniques. In the DSC thermograms of all BPs, there were two observable endothermic peaks with similar denaturation temperatures of about 80 and 102 °C, corresponding to the 8S and 13S globulins, respectively. The enthalpy changes (ΔH) of buckwheat globulins are also unaffected by the presence of lipids (2.5–17.8%), however, the width at half peak height (ΔT1/2) presenting the cooperativity of the transition from native to denatured state was related to the lipid content. DSC analyses in the presence of some protein perturbants (e.g., urea, SDS and DTT) showed that the structure of buckwheat globulins (especially 13S globulins) are mainly maintained by hydrogen bonding and hydrophobic interactions, and the presence of lipids may disturb the hydrophobic interactions of these globulins. The disulfide bonds only pay an important role in those globulins with high (17.8%) or low (2.5%) lipid contents. These results suggest that the presence of lipid affect the thermal properties of buckwheat globulins, especially the ability to resist the denaturant-induced denaturation, and a suitable amount of lipids be favorable for the maintenance of native protein conformation of 13S globulins.