Beta-conglycinin from soybean proteins. Isolation and immunological and physicochemical properties of the monomeric forms

Generation of New β-Conglycinin-Deficient Soybean Lines by Editing the lincRNA lincCG1 Using the CRISPR/Cas9 System

Soybean β-conglycinin is a major allergen that adversely affects the nutritional properties of soybean. Soybean deficient in β-conglycinin is associated with low allergenicity and high nutritional value. Long intergenic noncoding RNAs (lincRNAs) regulate gene expression and are considered important regulators of essential biological processes. Despite increasing knowledge of the functions of lincRNAs, relatively little is known about the effects of lincRNAs on the accumulation of soybean β-conglycinin. The current study presents the identification of a lincRNA lincCG1 that was mapped to the intergenic noncoding region of the β-conglycinin α-subunit locus. The full-length lincCG1 sequence was cloned and found to regulate the expression of soybean seed storage protein (SSP) genes via both cis- and trans-acting regulatory mechanisms. Loss-of-function lincCG1 mutations generated using the clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) system led to the deficiency of the allergenic α'-, α-, and β-subunits of soybean β-conglycinin as well as higher content of proteins, sulfur-containing amino acids, and free arginine. The dominant null allele LincCG1, and consequently, the β-conglycinin-deficient phenotype associated with the lincCG1-gene-edited line was stably inherited by the progenies in a Mendelian fashion. The dominant null allele LincCG1 may therefore be exploited for engineering/developing novel hypoallergenic soybean varieties. Furthermore, Cas9-free and β-conglycinin-deficient homozygous mutant lines were obtained in the T1 generation. This study is the first to employ the CRISPR/Cas9 technology for editing a lincRNA gene associated with the soybean allergenic protein β-conglycinin. Moreover, this study reveals that lincCG1 plays a crucial role in regulating the expression of the β-conglycinin subunit gene cluster, besides highlighting the efficiency of employing the CRISPR/Cas9 system for modulating lincRNAs, and thereby regulating soybean seed components.

Regulation of seed traits in soybean

Soybean (Glycine max) is an essential economic crop that provides vegetative oil and protein for humans, worldwide. Increasing soybean yield as well as improving seed quality is of great importance. Seed weight/size, oil and protein content are the three major traits determining seed quality, and seed weight also influences soybean yield. In recent years, the availability of soybean omics data and the development of related techniques have paved the way for better research on soybean functional genomics, providing a comprehensive understanding of gene functions. This review summarizes the regulatory genes that influence seed size/weight, oil content and protein content in soybean. We also provided a general overview of the pleiotropic effect for the genes in controlling seed traits and environmental stresses. Ultimately, it is expected that this review will be beneficial in breeding improved traits in soybean.

The role of the extension region on the structural and physicochemical characteristics of the α-subunit of β-conglycinin: implications of pH value and ionic strength

BACKGROUND

To clarify the role of the extension region on the structure-functional relationship of the α-subunit of β-conglycinin, α-subunit and its segment of the core region (αc-subunit) were expressed via an Escherichia coli system. Their physicochemical properties were compared under acid, neutral or alkaline conditions (pH 4.0, 7.0, and 8.0) and high or low ionic strength (μ = 0.05 and 0.5), respectively.

RESULTS

The results showed that the extension region contributed to increasing thermal stability, especially at low ionic strength under acidic and neutral conditions. The extension region stabilized the α-subunit with high solubility, low turbidity, and small particle size under neutral and alkaline conditions, whereas these impacts were suppressed at a high ionic strength and acidic conditions. Surface hydrophobicity of the α-subunit decreased under acidic and alkaline conditions without being interfered with by ionic strength.

CONCLUSION

It can be concluded that the extension region played different roles under different pH and ionic strength conditions. These factors should be specified carefully and speculated individually to explore the more detailed and profound nature of β-conglycinin at the submolecular level. The results could benefit a better understanding of the relationship between domain structure and functions of soybean protein. © 2022 Society of Chemical Industry.

Quantitative proteomic analyses reveal the dynamics of protein and amino acid accumulation during soybean seed development

Using high throughput tandem mass tag (TMT) based tagging technique, we identified 4172 proteins in three developmental stages: early, mid, and late seed filling. We mapped the identified proteins to metabolic pathways associated with seed filling. The elevated abundance of several kinases was observed from the early to mid-stages of seed filling, indicating that protein phosphorylation was a significant event during this period. The early to late seed filling stages were characterized by an increased abundance of proteins associated with the cell wall, oil, and vacuolar-related processes. Among the seed storage proteins, 7S (β-subunit) and 11S (Gy3, Gy4, Gy5) steadily increased in abundance during early to late stages of seed filling, whereas 2S albumin exhibited a decrease in abundance during the same period. An increased abundance of proteases, senescence-associated proteins, and oil synthesis proteins was observed from the mid to late seed filling stages. The mid to late stages of seed filling was also characterized by a lower abundance of transferases, transporters, Kunitz family trypsin, and protease inhibitors. Two enzymes associated with methionine synthesis exhibited lower abundance from early to late stages. This study unveiled several essential enzymes/proteins related to amino acid and protein synthesis and their accumulation during seed development. All data can be accessed through this link: https://massive.ucsd.edu/ProteoSAFe/dataset.jsp?task=38784ecbd0854bb3801afc0d89056f84. (Accession MSV000087577).

Confocal Fluorescence Microscopy Investigation for the Existence of Subdomains within Protein Storage Vacuoles in Soybean Cotyledons

In legumes, the seed storage proteins accumulate within specialized organelles called protein storage vacuoles (PSVs). In several plant species, PSVs are differentiated into subdomains that accumulate different kinds of proteins. Even though the existence of subdomains is common in cereals and legumes, it has not been reported in soybean PSVs. The two most abundant seed proteins of soybean, 7S and 11S globulins, have different temporal accumulation patterns and exhibit considerable solubility differences that could result in differential accretion of these proteins within the PSVs. Here, we employed confocal fluorescent microscopy to examine the presence or absence of subdomains within the soybean PSVs. Eosin-stained sections of FAA-fixed paraffin embedded soybean seeds, when viewed by confocal fluorescence microscopy, revealed the presence of intricate subdomains within the PSVs. However, fluorescence immunolabeling studies demonstrated that the 7S and 11S globulins were evenly distributed within the PSVs and failed to corroborate the existence of subdomains within the PSVs. Similarly, confocal scanning microscopy examination of free-hand, vibratome and cryostat sections also failed to demonstrate the existence of subdomains within PSVs. The subdomains, which were prominently seen in PSVs of FAA-fixed soybean seeds, were not observed when the seeds were fixed either in glutaraldehyde/paraformaldehyde or glutaraldehyde. Our studies demonstrate that the apparent subdomains observed in FAA-fixed seeds may be a fixation artifact.

A novel highly sensitive soy aptasensor for antigen β-conglycinin determination

β-Conglycinin, composed of three subunits (α', α and β), is the main allergen of soy protein which can cause severe allergic reactions, such as diarrhea, decreased growth performance and even death. Among them, the β subunit is more stable and difficult to remove, being one of the main nutritional inhibitors, which can be used to evaluate the concentration of β-conglycinin. However, there is no effective, accurate method for its β subunit rapid detection. Herein, we have successfully selected a high affinity β subunit aptamer (Kd = 6.9 nM) and developed a highly sensitive aptasensor. The aptasensor displayed high specificity and the β subunit at a concentration of 70-350 nM could be detected with a detection limit of 4.48 nM (3S/N). In addition, the recoveries of β subunit were more than 90%, demonstrating its practical properties for complicated conditions such as food quality control and disease diagnosis, without requiring expensive and sophisticated equipment.

Separation of Storage Proteins (7S and 11S) from Soybean Seed, Meals and Protein Isolate Using an Optimized Method Via Comparison of Yield and Purity

The primary purpose of this study was to extract β-conglycinin (7S) and glycinin (11S) from soybean seed, soybean meals and soybean protein isolate and compare their yield and purity. The previous methods were modified for the extraction and isolation of 7S and 11S globulins. The adjustment mainly included sample to solution ratio of 1:10 (previously 1:15). Comparing the yield of 11S fraction in Tris-HCl and water as extractable solutions, it was almost doubled in soybean seed (16.97% to 32.41%) with purity from 96 to 98% respectively. In case of soybean meal, samples yield increased from 45.46 to 61.86% with purity from 94 to 98%. On contrary, 7S yield was significantly improved in soybean protein isolate sample from 30.33 to 53.81% along with no contamination in its purity while soybean seed and soybean meal samples had less increase in both yield and purity in Tris-HCl and water as extractable solutions. Results of this study will bring new insights into soybean 7S and 11S separation and purification techniques as well as pave the way for their application in food industry.

Lactobacillus rhamnosus GG alleviates β-conglycinin-induced allergy by regulating the T cell receptor signaling pathway

Currently, the need for safe and effective methods for relieving allergies is an important concern. In this study, we evaluated the role of Lactobacillus rhamnosus GG (LGG) in alleviating β-conglycinin (β-CG)-induced allergies and elucidated the related molecular mechanisms. Typical allergy symptoms and inflammatory factors in the serum showed that LGG intervention effectively alleviated β-CG induced allergy in mice, which was better than natural recovery (NR). Intestinal villi were restored and lower levels of CD4+ T cells infiltrated after LGG intervention. We evaluated whether LGG intervention weakened the proliferation ability of the spleen cells of allergic mice, balancing between T/B cells and Th1/Th2 and Th17/Treg cytokines. Transcriptome analysis revealed that 4106 differentially expressed mRNAs were identified by comparing the LGG group and β-CG group, and 546 differentially expressed mRNAs were identified by comparing the LGG group and NR group. KEGG pathway analysis identified that the T cell receptor (TCR) signaling pathway was significantly enriched upon LGG intervention, and the upregulated Ifnar2 and the downregulated Tgfbr2, Il13r2 and Il4ra were further validated by qPCR analysis. Therefore, the above results fully revealed the important role of LGG in alleviating β-CG-induced allergies.

Overexpression of ATP sulfurylase improves the sulfur amino acid content, enhances the accumulation of Bowman-Birk protease inhibitor and suppresses the accumulation of the β-subunit of β-conglycinin in soybean seeds

ATP sulfurylase, an enzyme which catalyzes the conversion of sulfate to adenosine 5'-phosphosulfate (APS), plays a significant role in controlling sulfur metabolism in plants. In this study, we have expressed soybean plastid ATP sulfurylase isoform 1 in transgenic soybean without its transit peptide under the control of the 35S CaMV promoter. Subcellular fractionation and immunoblot analysis revealed that ATP sulfurylase isoform 1 was predominantly expressed in the cell cytoplasm. Compared with that of untransformed plants, the ATP sulfurylase activity was about 2.5-fold higher in developing seeds. High-resolution 2-D gel electrophoresis and immunoblot analyses revealed that transgenic soybean seeds overexpressing ATP sulfurylase accumulated very low levels of the β-subunit of β-conglycinin. In contrast, the accumulation of the cysteine-rich Bowman-Birk protease inhibitor was several fold higher in transgenic soybean plants when compared to the non-transgenic wild-type seeds. The overall protein content of the transgenic seeds was lowered by about 3% when compared to the wild-type seeds. Metabolite profiling by LC-MS and GC-MS quantified 124 seed metabolites out of which 84 were present in higher amounts and 40 were present in lower amounts in ATP sulfurylase overexpressing seeds compared to the wild-type seeds. Sulfate, cysteine, and some sulfur-containing secondary metabolites accumulated in higher amounts in ATP sulfurylase transgenic seeds. Additionally, ATP sulfurylase overexpressing seeds contained significantly higher amounts of phospholipids, lysophospholipids, diacylglycerols, sterols, and sulfolipids. Importantly, over expression of ATP sulfurylase resulted in 37-52% and 15-19% increases in the protein-bound cysteine and methionine content of transgenic seeds, respectively. Our results demonstrate that manipulating the expression levels of key sulfur assimilatory enzymes could be exploited to improve the nutritive value of soybean seeds.

Soy protein isolate supplemented silk fibroin nanofibers for skin tissue regeneration: Fabrication and characterization

Biocompatible soy protein isolate/silk fibroin (SPI/SF) nanofibrous scaffolds were successfully fabricated through electrospinning a novel protein blend SPI/SF. Prepared nanofibers were treated with ethanol vapor to obtain an improved water-stable structure. Fabricated scaffolds were characterized through scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), UV-VIS spectrophotometry and image analysis. The mean diameters of SPI/SF electrospun fibers were observed ranging between 71 and 160 nm. The scaffolds were found significantly stable for a prolong duration at the room temperature as well as at 37 °C, when placed in phosphate buffered saline, nutrient medium, and lysozyme-containing solution. The potential of fabricated scaffolds for skin tissue regeneration was evaluated by in vitro culturing of standard cell lines i.e., fibroblast cells (L929-RFP (red fluorescent protein) and NIH-3T3) and melanocytes (B16F10). The outcomes revealed that all the fabricated nanofibrous scaffolds were non-toxic towards normal mammalian cells. In addition, healing of full-thickness wound in rats within 14 days after treatment with a nanofibrous scaffold demonstrated its suitability as a potential wound dressing material. Interestingly, we found that nanofibers induced a noticeable reduction in the proliferation rate of B16F10 melanoma cells.

Soybean Mutants Lacking Abundant Seed Storage Proteins Are Impaired in Mobilization of Storage Reserves and Germination

Spontaneous and radiation-induced mutants of soybean, despite loss of abundant seed proteins, have been reported to grow and reproduce normally without any apparent physiological abnormalities. Here, we report the development and characterization of a soybean line (BSH-2) that lacks several abundant seed storage proteins. One-dimensional and high-resolution two-dimensional gel electrophoresis revealed the absence of the α' and α subunits of β-conglycinin and G1, G2, G4, and G5 glycinin in the newly developed mutant line (BSH-2). Like our earlier developed soybean mutant line (BSH-3), the seeds of BSH-2 also accumulated high levels of free amino acids as compared with wild-type DN47 seeds. An examination of the germination rates revealed that both BSH-2 and BSH-3 had significantly lower germination rates compared with the parent line DN47. Two-dimensional gel electrophoresis analysis demonstrated that these mutants had slower rates of mobilization of seed storage proteins. The delayed mobilization of storage proteins in BSH-2 and BSH-3 seeds was also correlated with a delayed induction of proteolytic activity in the mutants when compared to DN47. Similarly, qRT-PCR analysis revealed distinct expression pattern of genes involved in proteolytic pathway in the mutants when compared to DN47. Transmission electron microscopy observation of soybean seeds at two germination stages revealed striking differences in the breakdown of protein storage vacuoles and lipid bodies in the mutants. Our study demonstrates that BSH-2 and BSH-3 are compromised in mobilization of storage reserves and the absence of abundant storage proteins may affect the seed germination efficiency and post-germinative seedling establishment.

A Comparative Study on Fouling and Cleaning Characteristics of Soy Protein Isolate (SPI)

Fouling on heat exchanger surface is a severe problem in food industry. This study investigated the fouling and cleaning behaviors of soy protein isolates (SPI) in heat exchangers, using a previously established real-time monitoring laboratory system. SPI fouling deposit was formed at different surface temperatures of 80, 85 and 90 °C. For cleaning, the effect of the NaOH concentration was investigated. The fouling and cleaning behaviors of whey protein concentrate (WPC) were studied for a qualitative comparison. The two solution concentrations were kept at 6 wt%. Under the constant heat flux condition applied in the experiments, increasing the surface temperature significantly increased the fouling rate of SPI. SPI deposit was much easier to remove compared to WPC deposit. Visualization showed that the cleaning behavior of SPI was different from that of WPC in that it swelled rather quickly followed by the species seeping out from the swollen structure.

Development and Characterization of a Soybean Experimental Line Lacking the α' Subunit of β-Conglycinin and G1, G2, and G4 Glycinin

A soybean experimental line (BSH-3) devoid of a subset of seed storage proteins was developed by crossing a mutant donor line "HS99B" with a Chinese cultivar "Dongnong47" (DN47). One-dimensional and high-resolution 2-D gel electrophoresis revealed the absence of G1 (A1aB2), G2 (A2B1a), and G4 (A5A4B3) glycinin and the α' subunit of β-conglycinin in BSH-3 seeds. Despite the lack of these abundant seed proteins, BSH-3 seeds still accumulated 38% protein. BSH-3 seeds also accumulated high levels of free amino acids as compared with DN47 seeds, particularly arginine, and the amount of several essential amino acids were significantly elevated in BSH-3 seeds. Elevated accumulation of α and β-subunit of β-conglycinin, G5 glycinin, Kunitz trypsin inhibitor, and Bowman-Birk protease inhibitor indicates seed proteome rebalancing in BSH-3 seeds. Immunoblot analysis using sera from soybean allergic patients demonstrated the complete lack of a major allergen (α' subunit of β-conglycinin) in BSH-3 seeds. However, elevated levels of other allergens were found in BSH-3 seeds due to proteome rebalancing. Transmission electron microscopy observation of mature seeds of BSH-3 revealed striking differences in the appearance of the protein storage vacuoles when compared with DN47.

The analysis of the causes of protein precipitate formation in the blanched soymilk

This paper explored the causes of protein precipitate formation in blanched soymilk prepared by blanching soybeans through studying the changes in composition and amount of protein particles during its thermal processing. Compared with the traditional method of preparing soymilk, blanching changed the thermal aggregation behavior of protein particles. Results showed that when blanching was applied to soybeans, β-conglycinin (7S) was denatured in the blanched soybeans, which resulted in the fixation and aggregation of 7S prior to the grinding processing. Therefore, 7S lost its inhibitory ability on the growth of other protein aggregation, explaining the increased insoluble precipitates in the blanched soymilk.

Methodology for identification of pore forming antimicrobial peptides from soy protein subunits β-conglycinin and glycinin

Antimicrobial peptides (AMPs) inactivate microbial cells through pore formation in cell membrane. Because of their different mode of action compared to antibiotics, AMPs can be effectively used to combat drug resistant bacteria in human health. AMPs can also be used to replace antibiotics in animal feed and immobilized on food packaging films. In this research, we developed a methodology based on mechanistic evaluation of peptide-lipid bilayer interaction to identify AMPs from soy protein. Production of AMPs from soy protein is an attractive, cost-saving alternative for commercial consideration, because soy protein is an abundant and common protein resource. This methodology is also applicable for identification of AMPs from any protein. Initial screening of peptide segments from soy glycinin (11S) and soy β-conglycinin (7S) subunits was based on their hydrophobicity, hydrophobic moment and net charge. Delicate balance between hydrophilic and hydrophobic interactions is necessary for pore formation. High hydrophobicity decreases the peptide solubility in aqueous phase whereas high hydrophilicity limits binding of the peptide to the bilayer. Out of several candidates chosen from the initial screening, two peptides satisfied the criteria for antimicrobial activity, viz. (i) lipid-peptide binding in surface state and (ii) pore formation in transmembrane state of the aggregate. This method of identification of antimicrobial activity via molecular dynamics simulation was shown to be robust in that it is insensitive to the number of peptides employed in the simulation, initial peptide structure and force field. Their antimicrobial activity against Listeria monocytogenes and Escherichia coli was further confirmed by spot-on-lawn test.

Protein structural changes during processing of vegetable feed ingredients used in swine diets: implications for nutritional value

Protein structure influences the accessibility of enzymes for digestion. The proportion of intramolecular β-sheets in the secondary structure of native proteins has been related to a decrease in protein digestibility. Changes to proteins that can be considered positive (for example, denaturation and random coil formation) or negative (for example, aggregation and Maillard reactions) for protein digestibility can occur simultaneously during processing. The final result of these changes on digestibility seems to be a counterbalance of the occurrence of each phenomenon. Occurrence of each phenomenon depends on the conditions applied, but also on the source and type of the protein that is processed. The correlation between denaturation enthalpy after processing and protein digestibility seems to be dependent on the protein source. Heat seems to be the processing parameter with the largest influence on changes in the structure of proteins. The effect of moisture is usually limited to the simultaneous application of heat, but increasing level of moisture during processing usually increases structural changes in proteins. The effect of shear on protein structure is commonly studied using extrusion, although the multifactorial essence of this technology does not allow disentanglement of the separate effects of each processing parameter (for example, heat, shear, moisture). Although most of the available literature on the processing of feed ingredients reports effects on protein digestibility, the mechanisms that explain these effects are usually lacking. Clarifying these mechanisms could aid in the prediction of the nutritional consequences of processing conditions.

Soybean seeds overexpressing asparaginase exhibit reduced nitrogen concentration

In soybean seed, a correlation has been observed between the concentration of free asparagine at mid-maturation and protein concentration at maturity. In this study, a Phaseolus vulgaris K⁺ -dependent asparaginase cDNA, PvAspG2, was expressed in transgenic soybean under the control of the embryo specific promoter of the β-subunit of β-conglycinin. Three lines were isolated having high expression of the transgene at the transcript, protein and enzyme activity levels at mid-maturation, with a 20- to 40-fold higher asparaginase activity in embryo than a control line expressing β-glucuronidase. Increased asparaginase activity was associated with a reduction in free asparagine levels as a percentage of total free amino acids, by 11-18%, and an increase in free aspartic acid levels, by 25-60%. Two of the lines had reduced nitrogen concentration in mature seed as determined by nitrogen analysis, by 9-13%. Their levels of extractible globulins were reduced by 11-30%. This was accompanied by an increase in oil concentration, by 5-8%. The lack of change in nitrogen concentration in the third transgenic line was correlated with an increase in free glutamic acid levels by approximately 40% at mid-maturation.

Structural and functional analysis of various globulin proteins from soy seed

Storage proteins of soybean mostly consist of globulins, which are classified according to their sedimentation coefficient. Among 4 major types: 2S, 7S, 11S, and 15S of globulins, 7S and 11S constitute major fraction. The 11S fraction consists only of glycinin and 7S fraction majorly consists of β-conglycinin, small amounts of γ-conglycinin and basic 7S globulin (Bg7S). Glycinin exist as a hexamer while β-conglycinin as a trimer and Bg7S as a tetramer. Glycinin subunits are coded by 5 genes of a family, whereas about 15 genes are present for β-conglycinin subunits. Bg7S gene is present in four copies in soybean genome. Synthesis of all proteins takes place as a single polypeptide chain, which is cleaved after folding to yield different chains or subunits. Glycinin and β-Conglycinin are made for storage purpose. However, Bg7S has potential xylanase inhibition activity and protein kinase activity. Primary structure of Bg7S reveals 12 conserved cysteine residues involved in forming 6 disulfide bonds, which provides appreciable stability to protein. Secondary structure is predominately rich in β-sheets with few alpha helices. Bg7S shares structural similarity with various aspartic-proteases. In this review, our aim is to discuss sequence, structure, and function of various globulins present in Glycine max.

Stable and pH-sensitive protein nanogels made by self-assembly of heat denatured soy protein

In this study, we examined the possibility of preparing stable soy protein nanogels by simply heating homogeneous soy protein dispersion. The protein nanogels formed were characterized by z-average hydrodynamic diameter, polydispersity index, turbidity, ζ-potential, morphology, and their stability to pH and ionic strength change. Soy protein dispersion (1% w/v) was homogeneous around pH 5.9 where it had the lowest polydispersity index (∼0.1). Stable and spherical nanogels were formed by heating soy protein dispersion at pH 5.9 under 95 °C. They sustained constantly low polydispersity index (∼0.1) in the investigated pH range of 6.06-7.0 and 2.6-3.0. The nanogels were pH-sensitive and would swell with pH change. They were stable at 0-200 mM NaCl concentration. Denaturation of soy glycinin was the prerequisite for the formation of stable nanogels. Soy protein nanogels had a core-shell structure with basic polypeptides and β subunits interacting together as the hydrophobic core; and acid polypeptides, α', and α subunits locating outside the core as hydrophilic shell. The inner structure of soy protein nanogels was mainly stabilized by disulfide bonds cross-linked network and hydrophobic interaction. Soy protein nanogels made in this study would be useful as functional ingredients in biotechnological, pharmaceutical, and food industries.

Chitosan-Soyprotein Interaction as Determined by Thermal Unfolding Experiments

Chitosan interaction with soybean beta-conglycinin beta(3) was investigated by thermal unfolding experiments using CD spectroscopy. The negative ellipticity of the protein was enhanced with rising solution temperature. The transition temperature of thermal unfolding of the protein (T(m)) was 63.4 degrees C at pH 3.0 (0.15 M KCl). When chitosan was added to the protein solution, the T(m) value was elevated by 7.7 degrees C, whereas the T(m) elevation upon addition of chitosan hexamer (GlcN)(6) was 2.2 degrees C. These carbohydrates appear to interact with the protein stabilizing the protein structure, and the interaction ability could be evaluated from the T(m) elevation. Similar experiments were conducted at various pHs from 2.0 to 3.5, and the T(m) elevation was found to be enhanced in the higher pH region. We conclude that chitosan interacts with beta-conglycinin through electrostatic interactions between the positive charges of the chitosan polysaccharide and the negative charges of the protein surface.

Protective and reparative effects of peptides from soybean β-conglycinin on mice intestinal mucosa injury

Peptides derived from alcalase digestion of soybean β-conglycinin, containing 8.52% carbohydrate, exhibits an inhibition effect on pathogen adhesion or translocation to intestinal cells in vitro. In this study, the protective and reparative effects of β-conglycinin peptides on intestinal mucosa injury in vivo were studied using mice with dextran sulfate sodium (DSS)-induced intestinal mucosa injury. The results showed that β-conglycinin peptides contained approximately 21.77% glutamic acid (Glu), and significantly reduced the histological injury in mice both in the protective and reparative experiments. The myeloperoxidase activity of mice treated with β-conglycinin peptides decreased compared with those treated DSS in the positive control group. Immunohistochemical analysis also showed that β-conglycinin peptides inhibited the expression of inflammatory factor NF-κB/p65. These results suggested that peptides derived from soybean β-conglycinin exhibited protective and reparative effects on mice intestinal mucosa injury.

Role of soybean β-conglycinin subunits as potential dietary allergens in piglets

β-Conglycinin, a major seed-storage protein in soybeans, is one of the primary antigenic proteins responsible for soybean-meal hypersensitivity in weaned piglets. The protein is a heterotrimer composed of subunits α, α' and β. It is currently unknown which of the β-conglycinin subunits are allergenic for piglets. The aim of this study was to identify potential allergenic subunits of β-conglycinin for soybean sensitive piglets and to characterise these subunits by immunoglobulin (Ig) G and E immunoblotting, ELISA, 'skin prick' and whole blood histamine-release testing. The IgG and IgE binding capabilities of the purified α, α' and β subunits of β-conglycinin were determined by immunoblot analysis and ELISA with sera from β-conglycinin sensitised piglets. Skin prick testing and whole blood histamine release testing were also performed to detect the activated effector cell response to specific allergens. Specific IgG and E antibodies were identified that recognised all three subunits of β-conglycinin in the sera of β-conglycinin sensitised piglets. All three subunits of β-conglycinin elicited positive skin test and specific histamine release responses from the whole blood of β-conglycinin sensitised piglets. These results suggest that all three β-conglycinin subunits are potential allergens for piglets.

Effect of pH and pepsin limited hydrolysis on the structure and functional properties of soybean protein hydrolysates

Effects of limited enzymatic hydrolysis with pepsin on the functional properties and structure characteristics of soybean proteins were investigated. Hydrolysates with different incubation time (10 to 900 min) were prepared. Results showed that SPI hydrolyzed for 60 min exhibited the best emulsibility and the ability of resisting freezing/thawing. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis proved that pepsin can degrade glycinin but had little effect on the α' subunit of β-conglycinin. The structure unfolding reached the largest extent after incubation for 60 min and the soluble and flexible aggregates were formed. After 120 min, glycinin was degraded totally and β-conglycinin formed insoluble aggregates. Moreover, 2 methods were applied for the deactivation of pepsin to obtain final hydrolysates at pH 2.0 and 7.0, respectively. The structure analysis revealed that the unfolding extent and structure characteristic were different in these 2 conditions. When adjusting the pH value from 2.0 to 7.0, the unfolding protein molecular would reaggregate again at pH 7.0 due to the charge neutralization, and the hydrodynamic diameter and λmax absorbance decreased compared to pH 2.0. Moreover, some of the insoluble aggregates formed at pH 2.0 became soluble at pH 7.0, because of the salt-in phenomenon.

Acid induced gelation of soymilk, comparison between gels prepared with lactic acid bacteria and glucono-δ-lactone

The objective of this work was to compare the gelation of soymilk particles induced by the acidification of a commercial starter culture with that resulting by addition of glucono-δ-lactone (GDL). Structure formation was followed using rheology, and the microstructure was observed by confocal microscopy. Acidification of lactic acid bacteria resulted in a higher gelation pH (pH 6.29±0.05) compared to that of a gel induced by GDL (pH 5.9±0.04). This difference was attributed to the longer time available for rearrangements of the soymilk particles in soymilk with starter cultures compared to the fast acidification by GDL. In spite of the earlier gelation pH, there were no observed differences in the final gel stiffness measured at pH 5.1, the value of tan δ, the frequency dependence and the linear viscoelastic range of the gels measured at the final pH. Microstructural observations also showed a similar protein network structure.