Structure of soya glycinin and conglycinin gels

Gels of glycinin and conglycinin formed at various heating temperatures, in the absence and presence of 0.2M sodium chloride were characterised by transmission electron microscopy. In distilled water both proteins formed gels consisting of strands with a thickness of 10–15 nm. The strands of glycinin were very regular and cross sections of strands showed a hollow cylindrical structure. In the presence of sodium chloride, glycinin formed an aggregated gel structure at 85°C, but at 95°C an ordered strand structure was formed. Dissociation of the quaternary structure on heating and reassociation of subunits into regular strands were considered the most probable mechanisms for strand formation from glycinin. The aggregated structure at 85°C was interpreted as a transient state prior to dissociation. Conglycinin rich gels were less regular and more crosslinked than gels of glycinin. Also, the strands of conglycinin showed a complex mode of aggregation possibly in the form of double spirals. The addition of sodium chloride caused a denser and more aggregated structure at 75 and 85°C, but the effects were not as drastic as in the case of glycinin. Heating temperature had only minor effects on the gel structure in the range studied.     

Characterization of Fractionated Soy Proteins Produced by a New Simplified Procedure

It was possible to fractionate soy protein into two soy protein isolate fractions (>90% protein) enriched in either glycinin or β-conglycinin by using a new simplified procedure (referred to as the Deak procedure) employing CaCl₂ and NaHSO₃. The Deak procedure produced fractions with higher yields of solids, protein, and isoflavones, and similar protein purities as well as improved functional properties compared to fractions recovered by established, more complex soy protein fractionation procedures. The Deak glycinin-rich fraction comprised 15.5% of the solids, 24.4% of the protein, and 20.5% of the isoflavones in the starting soy flour, whereas the glycinin-rich fraction of the established procedure (Wu procedure) comprised only 11.6% of the solids, 22.3% of the protein, and 9.6% of the isoflavones. The Deak β-conglycinin-rich fraction comprised 23.1% of the solids, 37.1% of the protein, and 37.5% of the isoflavones in the starting soy flour, whereas the Wu β-conglycinin-rich fraction comprised only 11.5% of the solids, 18.5% of the protein, and 3.3% of the isoflavones. Protein purities were >80% for both fractions when using both procedures. The Wu procedure produced protein fractions with slightly higher solubilities and similar surface hydrophobicities; whereas, the fractions produced by the Deak procedure had superior emulsification and foaming properties and similar dynamic viscosity behaviors.     

Improving the functional properties of soy glycinin by enzymatic treatment. Adsorption and foaming characteristics

In this contribution we have determined the effect of limited enzymatic hydrolysis on the interfacial (dynamics of adsorption and surface dilatational properties) and foaming (foam formation and stabilization) characteristics of a soy globulin (glycinin, fraction 11S). The degree of hydrolysis (DH=0%, 2%, and 6%), the pH of the aqueous solution (pH=5 and 7), and the protein concentration in solution (at 0.1, 0.5 and 1 wt%) were the variables studied. The temperature and the ionic strength were maintained constant at 20 °C and 0.05 M, respectively. The rate of adsorption and surface dilatational properties (surface dilatational modulus, E, and loss angle) of glycinin at the air–water interface depend on the pH and DH. The adsorption decreased drastically at pH 5.0, close to the isoelectric point of glycinin, because of the existence of a lag period and a low rate of diffusion. The interfacial characteristics of glycinin are much improved by enzymatic treatment, especially in the case of acidic aqueous solutions. Hydrolysates with a low DH have improved functional properties (mainly foaming capacity and foam stability), especially at pH close to the isoelectric point (pI), because the native protein is more difficult to convert into a film at fluid interfaces at pH≈pI. The foam capacity depends on the rate of diffusion of protein to the interface and is much improved by the enzymatic treatment. Foam stability correlates with surface pressure and, to a minor extent, with surface dilatational modulus at long-term adsorption with few exceptions.     

天然大豆球蛋白亚基的分离纯化

利用变性剂脲和还原剂β-巯基乙醇解聚大豆球蛋白,在还原条件下通过DEAE琼脂糖凝胶F阴离子交换层析分离大豆球蛋白亚基,并对制备的亚基进行复性,从而建立了系统的分离纯化大豆球蛋白天然亚基的方法。对该方法分离亚基的产率和亚基的纯度进行评定,并利用大豆球蛋白免疫家兔制备的抗血清检测各种纯化亚基的免疫活性。结果表明：在还原条件下利用阴离子交换层析,可以有效地分离大豆球蛋白的碱性亚基和不同种类的酸性亚基。该方法的产率较高,以大豆球蛋白分离纯化碱性亚基及酸性亚基A1a,A2,A3,A4的产率分别为23．93％,14．95％,14．33％,12．06％,7．12％。制备的碱性亚基和酸性亚基A1a,A2,A3,A4的纯度分别为84．39％,90．48％,92．00％,65．91％,85．00％;纯化亚基能与抗大豆球蛋白血清特异性结合,具有免疫活性。     

Development of monoclonal antibodies and a competitive ELISA detection method for glycinin,an allergen in soybean

Soybean glycinin is a major food allergen causing anaphylaxis. A sensitive detection method for glycinin is needed to evaluate soybean allergies in food and feed products. In the present study, monoclonal antibodies (Mabs) against glycinin were prepared using purified glycinin as the immunogen. The generated Mabs, named 3B2 and 4B2, were identified as being IgG_2b and IgG_2a iso-types respectively, and exhibited high specificity to glycinin. Then we developed a competitive ELISA based on Mab 4B2 to measure glycinin which showed an IC₅₀ value of 1.7 ng/mL with a detection limit of 0.3 ng/mL, and the linear portion of the curve was 0.3–11.2 ng/mL. Recovery tests indicated that the competitive ELISA based on Mab 4B2 gave reliable reproducibility. The produced Mab 4B2 and the developed ELISA could provide a valuable tool for sensitive determination of glycinin and for future studies conducted to reveal the mechanism of how glycinin functions in anaphylaxis.     

Legumin allergens from peanuts and soybeans: effects of denaturation and aggregation on allergenicity

Legumin proteins Ara h 3 from peanuts and glycinin from soybeans are increasingly described as important allergens. The stability of an allergen's IgE binding capacity towards heating and digestion is considered an important characteristic for food allergens. We investigated the effects of heating and digestion on the IgE binding of Ara h 3 and glycinin. Both proteins are relatively stable to denaturation, having denaturation temperatures ranging from 70 to 92 degrees C, depending on their quaternary structure and the ionic strength. Aggregates were formed upon heating, which were partly soluble for glycinin. Heating slightly decreased the pepsin digestion rate of both allergens. However, heating did not affect the IgE binding capacity of the hydrolyzates, as after only 10 min of hydrolysis no IgE binding could be detected any more in all samples. Peanut allergen Ara h 1, when digested under equal conditions, still showed IgE binding after 2 h of hydrolysis. Our results indicate that the IgE binding capacity of legumin allergens from peanuts and soybeans does not withstand peptic digestion. Consequently, these allergens are likely unable to sensitize via the gastro-intestinal tract and cause systemic food allergy symptoms. These proteins might thus be less important allergens than was previously assumed.     

The interaction of zinc(II) and phytic acid with soya bean glycinin

Binding of phytic acid to Zn(II) free glycinin was not observed in 0.5 M KCl at pH 6.2. The addition of varying quantities of phytic acid to a Zn(II)- glycinin system at pH 6.2 ([KCl]=0.5 M ) initially resulted in binding of phytate and increased binding of Zn(II) to glycinin probably as a phytate-Zn(II)-glycinin complex. Further addition of phytate resulted in precipitation of zinc and protein. Bovine serum albumin also showed increased affinity for Zn(II) owing to the presence of phytic acid. Phytic acid-Zn(II) precipitates have a capacity of removing glycinin from solution, presumably by surface adsorption. The presence of soluble Zn(II) inhibits this adsorption. Bovine serum albumin is removed from solution by phytic acid-Zn(II) precipitates only when soluble zinc is present.     

腐竹生产工艺原理研究

本文从物理化学、生物化学的角度对腐竹生产时薄膜的形成机理，凝胶结构及强度的影响因素，改善腐竹色泽的方法以及豆浆温度控制问题进行了论述，提出提高腐竹产品质量的对策。     

Reconstitution of single molecular species from isolated subunits of glycinin

Ion-exchange HPLC systems using POROS 20 HQ and Mono Q HR 10/10 columns were applied to isolate glycinin subunits under denaturing conditions. Analyses by SDS-PAGE, N-terminal amino acid sequence, and sucrose density gradient centrifugation showed that the pseudoglycinin from the highly purified homo-subunit, A₃B₄, was reconstituted. The A₃B₄ pseudoglycinin was similar to the native glycinin with respect to molecular size, subunit structure, and secondary structure. The hexameric pseudoglycinin dissociated into trimers after long storage at pH 7.6.     

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.