Chuan-He Tang

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.

Fabrication and Characterization of Novel Antimicrobial Films Derived from Thymol-Loaded Zein–Sodium Caseinate (SC) Nanoparticles

The objective of this research was to fabricate novel antimicrobial films based on zein colloidal nanoparticles coated with sodium caseinate (SC), an emulsifier/stabilizer. Thymol-loaded zein-SC nanoparticles were prepared using an antisolvent technique, with the average particle size and zeta potential about 200 ± 20 nm and -40 mV, respectively. Zein-SC nanoparticle-based films exhibited higher mechanical resistance and water barrier capacity than the SC films and concomitant good extensibility as compared with zein films. Thymol loadings endowed zein-SC nanoparticle-based films with antimicrobial activity against Escherichia coli and Salmonella as well as DPPH radical scavenging activity. Water vapor permeability, microstructure, mechanical, and controlled release properties of the films were evaluated. The possible relationship between some selected physical properties and microstructure were also discussed. Atomic force microscopy (AFM) analysis indicated that thymol loadings resulted in the emergence phenomena of the nanoparticles to form large particles or packed structure, consisting of clusters of nanoparticles, within the film matrix, in a thymol loading dependent manner. The appearance of large particles or an agglomerate of particles may weaken the compactness of protein network of films and thus impair the water barrier capacity, mechanical resistance, and extensibility of the films. The release kinetics of thymol from nanoparticle-based films can be described as a two-step biphasic process, that is, an initial burst effect followed by subsequent slower release, and zein-SC nanoparticles within the films matrices gave them the ability to sustain the release of thymol. In addition, a schematic illustration of the formation pathway of zein-SC nanoparticle-based films with or without thymol was proposed to illuminate the possible relationship between some selected physical properties and the microstructure of the films.

Nanocomplexation between Curcumin and Soy Protein Isolate: Influence on Curcumin Stability/Bioaccessibility and in Vitro Protein Digestibility

The complexation of nanoparticles in unheated and heated (at 75-95°) soy protein isolate (SPI) with curcumin and the effects on curcumin stability/bioaccessibility and in vitro protein digestibility were investigated. The nanoparticles did not display noticeable changes in size and morphology upon nanocomplexation with curcumin, except their surface hydrophobicity. The encapsulation efficiency of curcumin progressively decreased with increasing initial curcumin concentration in the dispersion, while the load amount linearly increased. The solubility of curcumin in water was enhanced by the complexation above 98000-fold (vs free curcumin in water). The formation of the nanocomplexes considerably improved the storage stability of curcumin. In vitro simulated digestion experiments indicated that the complexation also improved the bioaccessibility of curcumin; the bioaccessibility was greatly impaired by hydrolysis-induced protein aggregation. Addtionally, the nanocomplexation significantly improved the in vitro protein digestibility of both unheated and heated SPI.

Formation of Amyloid Fibrils from Kidney Bean 7S Globulin (Phaseolin) at pH 2.0

The amyloid fibrils formed by heating 1.0% (w/v) kidney bean phaseolin (7S globulin) solution at pH 2.0 with an ionic strength of 20 mM at 85 degrees C were characterized using transmission electron microscopy (TEM), atomic force microscopy (AFM), binding of thioflavin T (Th T) and Congo Red dyes, and circular dichroism spectroscopy. The morphology of the formed fibrils was closely dependent upon heating time from 15 to 720 min. The diameters of the fibrils formed at various times were similar, but the mean contour length progressively increased with heating time. The Th T maximum fluorescence also progressively increased with heating time. The heating process caused remarkable changes in secondary, tertiary, and quaternary conformations of the phaseolin, but the extents of the changes were closely related to the heating time. With a short heating time (e.g., 15 min), the beta-strand content decreased from 38.7 to 22.9%, but further heating resulted in recovery of beta-strand structure. The tertiary and quaternary conformations gradually became flexible and unfolded upon heating. Gel electrophoresis analysis indicated that heating disrupted the polypeptides of phaseolin, leading to the formation of fragments with lower molecular mass (e.g., <10 kDa after 360 min). The results suggest that the amyloid fibril formation of phaseolin (7S globulin) involved the disruption of its polypeptides, as well as conformational changes at secondary, tertiary, and quaternary structural levels. This appears to be the first direct observation of amyloid fibrils from legume 7S storage globulin.

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.

Nanocomplexation of soy protein isolate with curcumin: Influence of ultrasonic treatment

Soy protein isolate (SPI) can act as effective nanocarriers for water-insoluble curcumin, however, the maximal capacity of this protein to load curcumin and molecular mechanism for the formation of the nanocomplexes are still little known. This work investigated the formation and properties of SPI-curcumin nanocomplexes formed at a low concentration of 0.05% (w/v), as well as the influence of a high intensity ultrasonic treatment on the nanocomplexation. Most of the particles in non- or ultrasonic-treated SPIs were present in nanoparticle form with z-average sizes of about 50-52nm. The load amount (LA) of curcumin in the non-treated nanocomplexes reached 103.9μg/mg SPI. The ultrasonic treatment of the protein solution further significantly increased the LA, while the LA was considerably decreased by the treatment after the nanocomplexation. The complexation with curcumin significantly increased the particle size and ζ-potential of both non- and ultrasonic-treated SPIs, but led to a considerable reduction in surface hydrophobicity, with the greater changes observed for ultrasonic-treated SPI. The nanocomplexation with SPIs remarkably improved the storage stability of curcumin, with much better improvement observed for the ultrasonic-treated SPI. Both the number and nature of hydrophobic sites are important for the nanoparticles in SPI to exhibit high capacity to load curcumin molecules. This study confirmed that SPI exhibited a high capacity to load water-insoluble curcumin, and an ultrasonic pretreatment could further improve its encapsulation efficiency and stability of curcumin.

Core–Shell Soy Protein–Soy Polysaccharide Complex (Nano)particles as Carriers for Improved Stability and Sustained Release of Curcumin

Using soy protein isolate (SPI) and soy-soluble polysaccharides (SSPS) as polymer matrixes, this study reported a novel process to fabricate unique core-shell complex (nano)particles to perform as carriers for curcumin (a typical poorly soluble bioactive). In the process, curcumin-SPI nanocomplexes were first formed at pH 7.0 and then coated by SSPS. At this pH, the core-shell complex was formed in a way the SPI nanoparticles might be incorporated into the interior of SSPS molecules without distinctly affecting the size and morphology of particles. The core-shell structure was distinctly changed by adjusting pH from 7.0 to 4.0. At pH 4.0, SSPS was strongly bound to the surface of highly aggregated SPI nanoparticles, and as a consequence, much larger complexes were formed. The bioaccessibility of curcumin in the SPI-curcumin complexes was unaffected by the SSPS coating. However, the core-shell complex formation greatly improved the thermal stability and controlled release properties of encapsulated curcumin. The improvement was much better at pH 4.0 than that at pH 7.0. All of the freeze-dried core-shell complex preparations exhibited good redispersion behavior. The findings provide a simple approach to fabricate food-grade delivery systems for improved water dispersion, heat stability, and even controlled release of poorly soluble bioactives.

Structural rearrangement of ethanol-denatured soy proteins by high hydrostatic pressure treatment.

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.

Development of Novel Zein-Sodium Caseinate Nanoparticle (ZP)-Stabilized Emulsion Films for Improved Water Barrier Properties via Emulsion/Solvent Evaporation

This work attempted to develop novel high barrier zein/SC nanoparticle (ZP)-stabilized emulsion films through microfluidic emulsification (ZPE films) or in combination with solvent (ethyl acetate) evaporation techniques (ZPE-EA films). Some physical properties, including tensile and optical properties, water vapor permeability (WVP), and surface hydrophobicity, as well as the microstructure of ZP-stabilized emulsion films were evaluated and compared with SC emulsion (SCE) films. The emulsion/solvent evaporation approach reduced lipid droplets of ZP-stabilized emulsions, and lipid droplets of ZP-stabilized emulsions were similar to or slightly lower than that of SC emulsions. However, ZP- and SC-stabilized emulsion films exhibited a completely different microstructure, nanoscalar lipid droplets were homogeneously distributed in the ZPE film matrix and interpenetrating protein-oil complex networks occurred within ZPE-EA films, whereas SCE films presented a heterogeneous microstructure. The different stabilization mechanisms against creaming or coalescence during film formation accounted for the preceding discrepancy of the microstructures between ZP-and SC-stabilized emulsion films. Interestingly, ZP-stabilized emulsion films exhibited a better water barrier efficiency, and the WVP values were only 40-50% of SCE films. A schematic representation for the formation of ZP-stabilized emulsion films was proposed to relate the physical performance of the films with their microstructure and to elucidate the possible forming mechanism of the films.

Physicochemical and conformational properties of buckwheat protein isolates: influence of polyphenol removal with cold organic solvents from buckwheat seed flours.

The effects of polyphenol removal from common buckwheat seed flours with cold aqueous organic solvents (including 95% ethanol, 70% 2-propanol, and 80% methanol, v/v) on the physicochemical and conformational properties of their protein isolates (BPI) were investigated. The extraction resulted in considerable reduction in its polyphenol content, especially protein-bound polyphenol content, and concomitant increase in its protein content. The efficiency of the removal of the polyphenols was much better in the 2-propanol case than in other two cases. The surface hydrophobicity of the proteins changed slightly, while the disulfide bond contents remarkably increased, partially at the expense of free sulfhydryl group contents. The protein solubility in the pH range of 7.0-11.0 and the proportion of undenatured globulins in BPI products were variably improved by the organic solvent extraction, and the extent of the improvements was highest in the 2-propanol case. Intrinsic emission fluorescence and far-UV and/or near-UV CD spectra showed that polyphenol removal resulted in significant changes in tertiary and/or secondary conformations of the proteins in BPI, and the changes were also related to the efficiency of the removal of the polyphenols. These results suggest that the physicochemical and conformational properties of BPI are closely related to its polyphenol level, and there is also a close relationship between its physicochemical properties and tertiary and/or secondary conformations.