Effects of AOT reverse micelle on properties of soy globulins

This study was focused on the influence of AOT reverse micelle on physical–chemical properties of 7S and 11S globulins from soy proteins, and compared with aqueous buffer extraction. The results showed that the contents of the surface hydrophobicity and SH groups of 7S and 11S globulins and SS bonds of 11S globulin, using AOT reverse micelle extraction, were augmented, and SS bonds of 7S globulin decreased. The thermal and rheological properties of 7S and 11S globulins extracted using the two methods were studied by differential scanning calorimetry (DSC) and rheometery. It was found that the peak denaturation temperature and heat of transition of 7S and 11S globulins with aqueous buffer extraction were different from that with AOT reverse micellar extraction. The AOT reverse micelle did not affect the gel properties of 11S globulin, while it influenced 7S globulin’s. Hardness, springiness, gumminess, adhesiveness and chewiness of 7S globulin from AOT reverse micelle were lower than that from aqueous buffer extraction, but gumminess was higher.     

COMPARATIVE STUDY OF STRUCTURAL CHARACTERISTICS AND THERMAL BEHAVIOR OF WHEY AND ISOLATE SOYBEAN PROTEINS

Electrophoretic profiles, sulfhydryl(SH)/disulfide (SS) groups content, and surface hydrophobicity (H₀) values of whey soybean proteins (WSP) and native soy isolates (NSI) were determined. WSP, composed mainly by Kunitz trypsin inhibitor (KTI), and lectin (L), has a H₀ value of 24.0 ± 1.0, which is 6.8 times lower than that of NSI ones, and SH/SS groups content in the same range of NSI. The thermal behavior of WSP and NSI was studied by differential scanning calorimetry (DSC). The WSP thermogram in water, similar to NSI, showed two main peaks (Tp values: 74.0 ± 0.5 C and 90.4 ± 0.8C) attributed to thermal denaturation of KTI and L, respectively. These endotherms are slightly affected by μ, whereas those of NSI are strongly affected (Tp of 7S and 11S peaks increase 17C and 20C respectively, by increasing NaCl concentration from 0 to 1M). WSP has low Ho values not noticeably affected by ionic strength changes, whereas NSI has higher Ho, that increase in saline media and favor intermolecular hydrophobic interactions. The consequent low tendency to protein aggregation by hydrophobic interactions in WSP would explain their lower thermal stability at high μ. Control proteins of both preparations (7S and 11S enriched fractions for NSI, and purified trypsin inhibitors, urease and lectin for WSP) were use to confirm these results.     

Physicochemical Properties of Isolated Soy Proteins from Normal, Broken or Damaged Seeds

Soybean quality depends on growing, harvesting and storage conditions. The amount of broken or otherwise damaged seeds tends to increase during storage and may affect the quality of products. Protein isolates from altered seeds have physicochemical properties less useful than those of normal seeds. The effect is substantial on viscosity, gel forming ability and emulsion stability. Isolated proteins from damaged seeds mixed with those of normal seeds altered proportionally their gelation and water retention capacity of the gels. Viscosity or water absorbing capacity of protein isolates may be used as simple indicators to evaluate quality.     

Interactions between tannins and proteins isolated from broad bean seeds (<Emphasis Type="Italic">Vicia faba</Emphasis> Major) yield soluble and non-soluble complexes

The binding of tannin fraction to protein fractions isolated from broad bean seeds was studied by precipitating potential and fluorescence quenching methods. The tannin fraction with high proanthocyanidins content was isolated from broad bean coats. Storage proteins of broad bean, 11S, 7S, and 2S, were isolated from broad bean cotyledons and purified. Gelatin, BSA, as well as broad bean 2S and 7S protein fractions exhibited similar shape of curves illustrating the effect of pH on protein precipitation and were precipitated by broad bean tannin fraction over the wide range of pH. For pea proteins isolate and 11S fraction of broad bean proteins, quite different effect of pH was observed. The relationships between the amount of protein–polyphenols complex precipitated and the content of tannin fraction were linear and characterized by high squared correlation coefficients ranging from 0.9613 to 0.9938. Among the protein fractions isolated from broad bean seeds, the highest precipitating potential was noted for 11S fraction, followed by 7S and 2S fractions and amounted to 1.63, 1.34, and 0.87, respectively. To characterize the association of proteins with phenolic compounds yielding formation of soluble complexes, fluorescence spectroscopy was applied. Similarly, the most extensive fluorescence quenching was observed in the case of 11S protein fraction.     

Purification and identification of interacting components in a wheat starch–soy protein system

The objective of this research was to quantify the solubility, hydrophobicity and interaction characteristics of wheat–starch proteins (puroindoline, gliadin and glutenin) and protein-containing soy fractions (soy flour isolate [SFI], SFI 7S and 11S fractions, hexane-extracted textured soy flour [TVP] isolate, TVP 7S and 11S fractions, expelled, extruded soy flour [TSP] isolate, TSP 7S and11S fractions). Functional characteristics were assessed in aqueous sucrose solutions at pH 5.5 and 7.5 after heating to 25, 50, and 100 °C. Textured soy protein fractions were more soluble and had higher surface hydrophobicity profiles than their untextured counterparts. Sucrose addition decreased hydrophobicity in the textured proteins but increased it in untextured proteins. Characteristics of the isolate, as a whole, appear to be dictated by those of its 11S moiety. Dissociation constants (K_d values) for soy protein and starch-derived puroindoline were determined and indicated an extremely short association in all cases. The 11S fractions formed a complex with puroindoline in solution; however 7S fractions did not.     

The role of a low molecular weight glutenin fraction in the cooking quality of durum wheat pasta

Durum wheat glutenin fractions, composed of two low molecular weight proteins DSG-1 and DSG-2 (durum wheat (Triticum durum Desf) sulphurrich glutenin fractions) were extracted from semolina samples using a low concentration of Na tetradecanoate after extracting albumins, globulins and gliadins. DSG proteins have a high? SH plus S? S content. A highly significant correlation was found between the ? SH plus S? S content of this DSG-rich fraction and the cooking quality of pasta (0.63, P <0.01 with firmness and 0.86, P <0.001 with the state of the surface of the cooked pasta) and this seems to be a functional relationship. The use of acetic acid at various molarities showed the presence of high molecular weight glutenin fractions with differing solubility properties. In this respect, differences were found between varieties which are placed in the same group according to the classification of durum wheats based upon the composition of high molecular weight glutenin subunits.     

Interactions between Whey Protein Isolate and Soy Protein Fractions at Oil–Water Interfaces: Effects of Heat and Concentration of Protein in the Aqueous Phase

ABSTRACT:  The 2 main storage proteins of soy—glycinin (11S) and β-conglycinin (7S)—exhibit unique behaviors during processing, such as gelling, emulsifying, or foaming. The objective of this work was to observe the interactions between soy protein isolates enriched in 7S or 11S and whey protein isolate (WPI) in oil–water emulsion systems. Soy oil emulsion droplets were stabilized by either soy proteins (7S or 11S rich fractions) or whey proteins, and then whey proteins or soy proteins were added to the aqueous phase. Although the emulsifying behavior of these proteins has been studied separately, the effect of the presence of mixed protein systems at interfaces on the bulk properties of the emulsions has yet to be characterized. The particle size distribution and viscosity of the emulsions were measured before and after heating at 80 and 90 °C for 10 min. In addition, SDS-PAGE electrophoresis was carried out to determine if protein adsorption or exchanges at the interface occurred after heating. When WPI was added to soy protein emulsions, gelling occurred with heat treatment at WPI concentrations >2.5%. In addition, whey proteins were found adsorbed at the oil–water interface together with 7S or 11S proteins. When 7S or 11S fractions were added to WPI-stabilized emulsions, no gelation occurred at concentrations up to 2.5% soy protein. In this case also, 7S or 11S formed complexes at the interface with whey proteins during heating.     

β-Conglycinin and glycinin soybean protein emulsions treated by combined temperature–high-pressure treatment

Most studies on functionality of soybean proteins have been made with total protein isolates, with the drawback to limit the knowledge of phenomena due to the important complexity of protein composition. In this study we have tried to better understand the behavior of soy emulsions by using their two partially purified fractions: β-conglycinin (7S) and glycinin (11S). Furthermore, we have assessed the combined effect of temperature (20–60 °C) and high pressure (0.1–600 MPa) on physicochemical, microstructural and rheological properties of oil-in-water emulsions prepared with 7S or 11S proteins at 7% (w/v). Our results show that 7S and 11S emulsions behaved differently under the combined treatments and that 7S protein was responsible for the global properties of soybean emulsions, whereas 11S proteins exerted a negligible effect. From 400 MPa and at 60 °C, we have noticed for 7S emulsions an increase of flocculation and gelation, largely confirmed by confocal microscopy due to aggregation between adsorbed and aqueous 7S proteins. Globally we have evidenced that temperature reinforces the effect of high pressure and that the threshold to obtain some changes is 400 MPa. The very different behavior of 7S and 11S proteins in emulsions under treatments could help to orientate their commercial use as function of planed treatments.     

pH and ultrasound driven structure-function relationships of soy protein hydrolysate

The structural, thermodynamic and functional properties of soy protein hydrolysate (SPH) modified by treatment at different pH values (3, 5, and 9 and pH 7 as control) followed by ultrasound treatment (240 W, 30 min) were investigated. The treatment of SPH at alkaline pH combined with ultrasound treatment resulted in a reduction in the particle size and turbidity, enhancement in the surface negative charge and disulfide bond (SS) content, and exposure of more surface sulfhydryl (SH) groups, resulting in increased surface hydrophobicity and fluorescence intensity compared to those of the samples treated at pH 3–7. In addition, the alkaline-treated samples were more structurally stable than those treated at other pH values, having higher denaturation temperatures and enthalpies; moreover, these samples had higher solubility and emulsifying and foaming capacities. In addition, ultrasound-assisted pH treatment altered the secondary and tertiary structures of SPH by altering the covalent and non-covalent interactions, although there was no effect on the molecular weight distribution of proteins. In conclusion, ultrasound-assisted pH treatment is an effective method to improve physicochemical properties of SPH for applications in the food industry.     

Functional properties of protein isolates,globulin and albumin extracted from Ginkgo biloba seeds

In this study, the functional properties of Ginkgo seed protein isolate (GPI), Ginkgo seed globulin protein (GGP) and Ginkgo seed albumin protein (GAP) extracted from Ginkgo biloba seeds were investigated. The protein contents of GPI, GGP and GAP were 91.0%, 93.4% and 87.8%, respectively in the samples in which the sugar, polyphenol and crude fibre were removed by the preparation procedure. For functional properties of Ginkgo seed proteins in the natural state, GAP showed the highest oil-absorption capacity (9.3 ml/g), foaming capacity (67.8%), emulsifying capacity (65.4%) and emulsion stability (90.6%); while GPI showed the highest water absorption capacity (1.93 ml/g), and GGP showed the highest foam stability (55.5%). The differences of the chemical components, surface hydrophobicity, disulphide bond (SS) and sulfhydryl group (SH) contents of GPI, GGP and GAP, which were correlated significantly with functional properties of Ginkgo seed proteins, were also investigated. The improved functional properties, such as water absorption capacity, solubility, foaming properties and emulsifying properties of Ginkgo seed proteins were observed in a pH range of 8.0–10.0 or sodium chloride concentration of 0.5–0.75 M.     

Texture and rehydration properties of texturised soy protein: analysis based on soybean 7S and 11S proteins

Soy protein, one of the most commonly used raw materials for texturised vegetable protein, has an important influence on texturised soy protein (TSP) with its 7S and 11S fractions. In this study, soy 7S and 11S proteins were extracted from soybean isolate and added back to the raw material to prepare TSP and analyse the effect of both on the physical properties of TSP. The results showed that the addition of 5% soy 7s or 11s protein increased the water-holding capacity (up to 9.04%) and rehydration rate (up to 25.71%) of TSP. Compared with adding soy 11s protein, adding soy 7s protein has a faster rehydration rate at a lower temperature (30 and 45 °C). After extrusion, the content of free sulphhydryl groups, total sulphhydryl groups, and disulphide bonds was significantly reduced (P < 0.05). The extrusion treatment caused degradation of the protein chains, and the proteins mainly formed insoluble polymers. Electrophoretic analysis revealed that the sodium dodecyl-sulphate (SDS) reducing the extractable rate of the precipitate after SDS non-reduction extraction of the TSP added with 5% soy 7S and 11S proteins were lower than that of the control. The proportion of different soybean protein components in TSP could change its texture, water-holding, and rehydration characteristics of it, which provides a new method for the characteristics design of TSP.     

Improving surface functional properties of tofu whey-derived peptides by chemical modification with fatty acids

Effect of acylation with saturated fatty acids on surface functional properties of tofu whey-derived peptides was investigated. Tofu whey (TW) and soy proteins (7S, 11S, and acid-precipitated soy protein [APP]) were hydrolyzed by Protease M 'Amano' G, and resulting peptide mixtures were acylated with esterified fatty acids of different chain length (6C to 18C) to form a covalent linkage between the carboxyl group of fatty acid and the free amino groups of peptide. Acylation significantly (P < 0.05) increased emulsifying properties of 7S, 11S, and APP peptides independent of fatty acid chain length. Acylation decreased water binding capacity although oil binding capacity of acylated tofu whey ultra filtered fraction (UFTW < 3 kDa), 7S- and 11S-peptides were improved compared to native peptides. 7S peptides acylated with long chain fatty acids had shown significant higher surface hydrophobicity as in contrast with acylated UFTW < 3 kDa and APP peptides. Fluorescence spectra studies revealed structural conformation of acylated soy peptides as compared to native peptides. This study shows that chemical modification with fatty acids can further affect functional properties of soy proteins.     

Effect of pea proteins extraction and vicilin/legumin fractionation on the phase behavior in admixture with alginate

Soluble and natural mixed pea proteins (PP) were extracted from defatted pea seeds according to acidic precipitation (PPP) or ultrafiltration/diafiltration (PPDF) procedures. The isolates contained proteins with a low level of denaturation. Mixed pea globulins isolates presented quite similar solubility and thermal profiles, also a similar polypeptide composition. Vicilin/convicilin 7S (Vic) and legumin 11S (Leg) fractions were obtained by batch chromatography using a salt gradient for the elution. Several incompatible systems were built by mixing the pea proteins with an anionic polysaccharide (sodium alginate, SA), when biopolymers were both negatively charged. Most of mixtures exhibited a phase separation phenomenon. From phase diagrams, experimental binodal curves obtained with either mixed globulins or legumin fraction were apparently very close. However phase boundary was better-defined with the Leg fraction. No macroscopic phase separation was evidenced for mixtures with the vicilin fraction. Microstructure of the PP-SA mixtures was investigated by confocal microscopy (CLSM) according to PP composition and biopolymer initial composition. The Leg-SA and most of PPP-SA mixtures exhibited a droplet-like structure, while structure of PPDF-SA mixtures was aggregated-like. With mixed PP, an alginate entrapment within the PP-enriched phase would disturb phase separation. Also density and shape of the protein-enriched microdomains influenced kinetics of demixing. Polydispersity within the PP-SA mixtures, in terms of wide range molecular weights distribution and charge heterogeneity would explain such differences.     

Characterization of Physicochemical Properties and IgE‐Binding of Soybean Proteins Derived from the HHP‐Treated Seeds

The aim of this work was to evaluate the characterization of physicochemical properties and IgE‐binding of soybean proteins derived from the high hydrostatic pressure (HHP) treated seeds. Soybean seeds were treated by HHP at different pressures, and changes in the physicochemical properties of soybean proteins were characterized by proteins solubility, free sulfhydryl (SH) content, surface hydrophobicity, and secondary structures. Sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE) and enzyme‐linked immunoabsorbent assay (ELISA) were used to define the proteins patterns and IgE‐binding ability. The results showed that HHP treatment in the ranges of 0 to 500 MPa led to a slight but gradual decline in free SH content. The solubility and hydrophobicity of soybean proteins increased sharply from 100 to 200 MPa, and gradually decreased upon the further increase of pressure. The α‐helix and β‐sheets contents of soybean proteins decreased, while the random coil content increased. The SDS‐PAGE showed that HHP treatment of 100 to 200 MPa could dissociate the proteins, breaking the aggregates into smaller units, while the treatment ranging from 300 to 500 MPa could induce the proteins aggregation into larger units. Moreover, the ELISA revealed that the IgE‐binding of soybean proteins after HHP treatment at 200 MPa decreased 61.7% compared to the untreated group. Our findings suggested that HHP processing could not only modify the physicochemical properties of soybean proteins, but also significantly reduce its IgE‐binding at an appropriate pressure level.     

黑豆蛋白的分级提取及黑豆花色苷的成分鉴定

以黑豆为原料,添加不同浓度(0、5、10、15、20、25 mmol/L)的不同二价阳离子(Ca~(2+)、Mg~(2+)和Zn~(2+))分级提取黑豆蛋白,经冷冻干燥后用凯氏定氮法测得蛋白质量浓度,并对所得蛋白级分(7S、11S)的纯度和得率进行分析。结果表明,黑豆提取过程中所加入二价阳离子的类型及浓度显著影响7S和11S球蛋白的得率和纯度。利用综合平衡法,最终选定添加10 mmol/L的Mg2+分级提取黑豆球蛋白,得到7S蛋白纯度和得率分别为(86.29±3.25)%和(2.90±0.14)%,11S蛋白纯度和得率分别为(87.42±3.30)%和(9.11±0.28)%。用乙醇法提取黑豆花色苷,测得黑豆中总花色苷含量为(0.58±0.03)mg/g,总酚含量为(2.22±0.12)mg/g,对黑豆花色苷进行高效液相色谱-串联质谱分析,其组成成分为飞燕草色素-3-O-葡萄糖苷、矢车菊色素-3-O-葡萄糖苷、牵牛花色素-3-O-葡萄糖苷和锦葵花色素-3-O-葡萄糖苷。     

大豆7S和11S球蛋白的结构和功能性质

主要介绍大豆７Ｓ和１１Ｓ球蛋白的结构和功能性质，大豆蛋白质各个成分的分子量有所不同，按超速离心分离系数可分为２Ｓ，７Ｓ１１Ｓ和１５Ｓ４个组份。７Ｓ组份占总蛋白质的３０．９％，它是由４种不同大豆蛋白民组成，１１Ｓ组份占总大豆蛋白质的４１％，而且都是单一的１１Ｓ球蛋白，１１Ｓ球蛋白的等电点为ｐＨ４．６４。     

Physicochemical properties of whole soybean curd prepared by microbial transglutaminase

Whole soybean curd (WSC) was manufactured using micronized full-fat soybean (MFS) powder and microbial transglutaminase (TGase). The WSC prepared with 15% MFS had typical soybean curd texture with a hardness of 513 dyne/cm². It was confirmed that 7S and 11S protein fractions as major soy proteins disappeared in SDS-PAGE. Also, WSC prepared with 15% MFS and 10% TGase had excellent textural properties with a hardness of 645 dyne/cm² and springiness of 0.98. Addition of 0.5% gelatin in WSC prepared with 15% MFS and 5% TGase resulted in higher hardness (708 dyne/cm²) and springiness (0.98), as well as the highest values of G′ and G″. The surface properties of WSC were observed using a SEM, indicating the interrelationship of higher hardness and compact protein network filled with small cells. It was concluded that WSC prepared after heat treatment of 15% MFS at 95°C for 5 min, followed by an enzyme reaction with 10% TGase for 1 h, had more enhanced hardness and springiness than commercial WSC. Despite the addition of 5% TGase, WSC with improved textural properties can be manufactured by the fortification of 0.5% gelatin.     

Functional and conformational characterisation of walnut protein obtained through AOT reverse micelles

Walnut protein was extracted from defatted walnut flour by bis (2‐ethylhexyl) sodium sulfosuccinate (AOT) reverse micellar system and alkali solution with isoelectric precipitation. The functional and conformational characteristics of two proteins were investigated and compared. Walnut protein obtained through AOT reverse micelles was found to have higher extraction yield, solubility, emulsifying activity, foam capacities, water‐ and oil‐holding capacity compared to the protein from alkali solution along with isoelectric precipitation, while the surface hydrophobicity (H₀), contents of disulphide bond (SS) and sulfhydryl group (SH) were relatively lower. The differences of H₀, SS and SH contents could be due to the conformational changes of walnut proteins using two extraction methods. FTIR spectra and data showed that the reverse micelles caused the decrease in α‐helix, β‐sheet, random and β‐turn of walnut protein, the increase in the side‐chain structure content, which could be responsible for the modification of functional properties.     

Physicochemical Properties of 7S and 11S Protein Mixtures Coagulated by Glucono-δ-lactone

ABSTRACT: Blends of 7S and 11S proteins with added glucono-δ-lactone were investigated to study the effects of protein composition on gelation. The pH, water-holding capacity, textural, and color properties of the gels formed were studied at a constant temperature as a function of time. Generally high 11S to 7S ratios produced gels of higher hardness, cohesiveness, gumminess, and L values than those of the rest. 11S formed faster acid-induced gels compared with those containing low proportions of 11S. From the data, it was predicted that fractions of 7S:11S differing by 1:10 will form gels with similar physicochemical properties when the coagulating times (at 60 °C) differed by 20 min.     

高强度超声处理对大豆7S和11S球蛋白结构和理化性质的影响

以大豆7S和11S球蛋白为对象，研究了高强度超声处理（150、450、1350 W）在不同时间条件（15、30 min）下对7S和11S结构和理化性质的影响。结果表明:超声处理不改变7S和11S的一级结构，但能够使二级结构中各组分含量发生改变。同时，7S和11S的荧光强度在超声处理后降低，表面疏水性（H₀）显著增加(P<0.05)。粒径分布测定显示7S和11S经超声处理后液滴粒径分布更加均匀，蛋白溶液的稳定性有所提升。DSC结果可以看出，超声后7S的焓值（ΔH）从1.22 J/g最多下降至0.17 J/g，11S从1.41 J/g最多下降至0.53 J/g，展开蛋白质结构所需的能量更少。在理化性质方面，超声处理后7S和11S的乳化活性和乳化稳定性显著增加(P<0.05)，溶解度最多分别提高了12.85%和10.57%。此外，冷冻扫描电子显微镜（Cryo-SEM）观察微观结构显示，7S和11S超声后从较为有序的网状聚集状态转变为无序的状态。因此，采用高强度超声处理能够显著影响7S和11S的结构和理化性质。