Insight into the interaction and binding mechanism of a natural nonnutritive sweetener mogroside V with soybean protein isolates based on multi-spectroscopic techniques and computational simulations

As a natural low-calorie sweetener, Mogroside V (Mog-V) has gradually become one of the alternatives to sucrose with superior health attributes. However, Mog-V will bring unpleasant aftertastes when exceeding a threshold concentration. To investigate the possibility of soy protein isolates (SPIs), namely β-conglycinin (7S), and glycinin (11S) as flavor-improving agents of Mog-V, the binding mechanism between Mog-V and SPIs was explored through multi-spectroscopy, particle size, zeta potential, and computational simulation. The results of the multi-spectroscopic experiments indicated that Mog-V enhanced the fluorescence of 7S/11S protein in a static mode. The binding affinity of 7S-Mog-V was greater compared with 11S-Mog-V. Particle size and zeta potential analysis revealed that the interaction could promote aggregation of 7S/11S protein with different stability. Furthermore, computational simulations further confirmed that Mog-V could interact with the 7S/11S protein in different ways. This research provides a theoretical foundation for the development and application of SPI to improve the flavor of Mog-V, opening a new avenue for further expanding the market demand for Mog-V.

Formation of thermal-induced microgels from soy protein hydrolysates: Effects of selective proteolysis on glycinin/β-conglycinin

This study explored the impact of selective proteolysis on the formation of thermally induced soy protein microgels. Glycinin hydrolysate (GH) and β-conglycinin hydrolysate (CH) were obtained by subjecting soy protein isolate to selective proteolysis for different hydrolysis time (10-90 min), as confirmed by SDS-PAGE. In the early stages of hydrolysis, free sulfhydryl, surface hydrophobicity, storage modulus (G') and loss modulus (G″) of GH and CH increased, which enhanced their gelling potential. However, as hydrolysis time increased, the gel properties of the hydrolysates progressively weakened. Structural characterization of microgels revealed that GH yielded microgels with smaller particle sizes and coarser and relatively dispersed granular structures, while CH resulted in microgels with lower potential values, smoother surfaces, and lumps resembling strand-like formations. Analysis of the structure and intermolecular force of microgels showed that the microgel formed by the GH gradually tended to be disordered, whereas the secondary structure of microgels formed by CH showed lower random coil content, resulting in a dense gel network aggregated through disulfide bonding, hydrophobic interactions and hydrogen bonding as demonstrated by frequency-dependent storage moduli measurements. Overall, this study presents a thorough characterization of microgels and shows that they can be tailored by selective proteolysis, which enables controlling the β-conglycinin/glycinin ratio of soy protein.

Esterified Soy Proteins with Enhanced Antibacterial Properties for the Stabilization of Nano-Emulsions under Acidic Conditions

Soy protein isolate (SPI), including β-conglycinin (7S) and glycinin (11S), generally have low solubility under weakly acidic conditions due to the pH closed to their isoelectric points (pIs), which has limited their application in acidic emulsions. Changing protein pI through modification by esterification could be a feasible way to solve this problem. This study aimed to obtain stable nano-emulsion with antibacterial properties under weakly acidic conditions by changing the pI of soy protein emulsifiers. Herein, the esterified soy protein isolate (MSPI), esterified β-conglycinin (M7S), and esterified glycinin (M11S) proteins were prepared. Then, pI, turbidimetric titration, Fourier transform infrared (FTIR) spectra, intrinsic fluorescence spectra, and emulsifying capacity of esterified protein were discussed. The droplet size, the ζ-potential, the stability, and the antibacterial properties of the esterified protein nano-emulsion were analyzed. The results revealed that the esterified proteins MSPI, M7S, and M11S had pIs, which were measured by ζ-potentials, as pH 10.4, 10.3, and 9.0, respectively, as compared to native proteins. All esterified-protein nano-emulsion samples showed a small mean particle size and good stability under weakly acidic conditions (pH 5.0), which was near the original pI of the soy protein. Moreover, the antibacterial experiments showed that the esterified protein-based nano-emulsion had an inhibitory effect on bacteria at pH 5.0.

Complexation of soybean protein isolate with β-glucan and myricetin: Different affinity on 7S and 11S globulin by QCM-D and molecular simulation analysis

•

The ternary complex of SPI, β-glucan and myricetin was prepared, and the interaction mechanism was studied.

•

QCM-D was used to explore the binding affinity of 7S and 11S to β-glucan and myricetin.

•

Molecular docking analysis indicated that 11S protein has a stronger binding capacity compared with 7S.

The complexation of soybean protein isolate (SPI) with β-glucan (DG) and myricetin (MC) was focused in this study. UV-Vis, circular dichroism and 3D fluorescence analysis jointly proved that interaction with DG and MC altered the structures of SPI, whose β-sheet decreased to 29 % and random coil increased to 35 %, respectively. Moreover, the microenvironment of tryptophan and tyrosine from protein were changed. The ternary complex performed a different molecular weight distribution, showing a larger molecular weight of 1.17×10⁶ g/mol compared with SPI verified by gel permeation chromatography (GPC). And it was further evidenced by Quartz Crystal Microbalance with Dissipation (QCM-D) and molecular docking that glycinin (11S) possessed a better affinity toward DG and MC compared with β-conglycinin (7S), which indicated stronger binding ability through hydrogen bonds. The successful preparation of SPI-DG-MC complex will advance the application of soybean resource as a functional food ingredient.

Increased sulfur-containing amino acid content and altered conformational characteristics of soybean proteins by rebalancing 11S and 7S compositions

Soybean proteins are limited by their low contents of methionine and cysteine. Herein, 7S globulin accumulation was reduced using RNA interference to silence CG-β-1 expression, and the content of the A2B1a subunit was largely increased under the soybean seed-specific oleosin8 promoter. The results showed that the sulfur-containing amino acid content in soybean seeds drastically improved, reaching 79.194 nmol/mg, and the 11S/7S ratio had a 1.89-fold increase compared to the wild-type acceptor. The secondary structures of 11S globulin were also altered, and the β-sheet content increased with decreasing β-turn content, which was confirmed by Fourier transform infrared spectroscopy, Raman spectroscopy and circular dichroism analysis. Our findings suggested that raising the accumulation of 11S glycinin at the expense of reducing the content of 7S globulin is an attractive and precise engineering strategy to increase the amount of sulfur-containing amino acids, and soybean proteins with A2B1a subunits of 11S isolates improved, and β-subunits of 7S fractions reduced simultaneously might be an effective new material for food production.

Lyotropic liquid crystal-based transcutaneous peptide delivery system: Evaluation of skin permeability and potential for transcutaneous vaccination

Transcutaneous drug delivery is a promising method in terms of drug repositioning and reformulation because of its non-invasive and easy-to-use features. To overcome the skin barrier, which is the biggest challenge in transcutaneous drug delivery, a number of techniques, such as microemulsion, solid-in-oil dispersions and liposomes, have been studied extensively. However, the low viscosity of these formulations limits drug retention on the skin and reduces patient acceptability. Although viscosity can be increased by adding a thickening reagent, such an addition often alters formulation nanostructures and drug solubility, and importantly, decreases skin permeability. In this study, a gel-like lyotropic liquid crystal (LLC) was used as a tool to enhance skin permeability. In particular, we prepared 1-monolinolein (ML)-based LLCs with different water contents. All LLCs significantly enhanced skin permeation of a peptide drug, an epitope peptide of melanoma, despite their high viscoelasticity. Fourier transform infra-red spectroscopic analysis of the skin surface treated with the LLCs revealed that the gyroid geometry more strongly interacted with the lamellar structure inside the stratum corneum (SC) than the diamond geometry. Finally, as the result of the in vivo tumor challenge experiment using B16F10 melanoma-bearing mice, the LLC with the gyroid geometry showed stronger vaccine effect against tumor than a subcutaneous injection. Collectively, ML-based LLCs, especially with the gyroid geometry, are a promising strategy to deliver biomacromolecules into skin. STATEMENT OF SIGNIFICANCE: Transcutaneous drug delivery is a promising method for drug repositioning and reformulation because of its non-invasive and easy-to-use features. To overcome the skin barrier, which is the biggest challenge in transcutaneous drug delivery, we used a gel-like lyotropic liquid crystal (LLC) as a novel tool to enhance skin permeability. In this paper, we demonstrated that an LLC with a specific liquid crystalline structure has the highest skin permeation enhancement effect for a peptide antigen as a model drug. Moreover, the peptide antigen-loaded LLC showed a vaccine effect that was comparable to a subcutaneous injection in vivo. This study provides a basis for designing a transcutaneous delivery system of peptide drugs with LLC.

Changes of Soybean Protein during Tofu Processing

Tofu has a long history of use and is rich in high-quality plant protein; however, its production process is relatively complicated. The tofu production process includes soybean pretreatment, soaking, grinding, boiling, pulping, pressing, and packing. Every step in this process has an impact on the soy protein and, ultimately, affects the quality of the tofu. Furthermore, soy protein gel is the basis for the formation of soy curd. This review summarizes the series of changes in the composition and structure of soy protein that occur during the processing of tofu (specifically, during the pressing, preservation, and packaging steps) and the effects of soybean varieties, storage conditions, soybean milk pretreatment, and coagulant types on the structure of soybean protein and the quality of tofu. Finally, we highlight the advantages and limitations of current research and provide directions for future research in tofu production. This review is aimed at providing a reference for research into and improvement of the production of tofu.

Gelation of food protein-protein mixtures

Gelation of proteins is one of the principal means to give desirable texture to food products. Gelation of individual proteins in aqueous solution has been investigated intensively in the past, but in most food products the system contains mixtures of different types of proteins. Therefore one needs to consider interaction between different proteins both before and during gelation. Most food proteins can be classified as globular proteins, but casein and gelatin are also important food proteins. In this review the focus is on gelation induced by heating or cooling, which is the most commonly used method. After briefly discussing general features of protein aggregation and gelation, the literature on gelation of mixtures of different types of globular proteins is reviewed as well as that of mixtures of globular proteins with gelatin or with casein. The effect on the gel stiffness and the microstructure of the gelled mixtures will be discussed in terms of different scenarios that can be envisaged: independent aggregation and gelation, co-aggregation and phase separation.

Vertically sheathing laminar flow-based immunoassay using simultaneous diffusion-driven immune reactions

Simultaneous infusion of primary and secondary antibodies of different diffusivity into vertical laminar flows enables the improved immune reactions.