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.     

Effect of dextran glycation on nanofibril assembly of soya β‐conglycinin at pH 2.0 and the pH stability of nanofibrils

In this study, we investigated the effects of dextran glycation on soya β‐conglycinin self‐assembly into nanofibrils at 85 °C and pH 2.0, as well as their stability at pH 2.0–10.0. Although the hydrolysis rate of β‐conglycinin decreased, glycation significantly increased the structural change rate in the initial stage of nanofibril formation and the growth of nanofibril. It is suggested that the glycation of three subunits (α′, α, β) in β‐conglycinin may promote fibril assembly because the extension regions of α′ and α subunits play an important role in affecting the rate of structural changes in fibril formation. At neutral pH, conjugate nanofibrils are highly dispersible and transparent and remained greater structural stability compared with mixture. The improvement stability of conjugate nanofibrils may be contributed to dextran which provides some steric hindrance to prevent the aggregation of nanofibrils; this would also facilitate the application of soya β‐conglycinin nanofibrils in food industry.     

The zinc(II) binding sites of soya bean glycinin

Binding of zinc by glycinin was determined in 0.5 M KCl at pH 6.2. The number of binding sites in the native protein was 51 for 8.5 μM glycinin. Protein modification studies identified the histidine residues as one of the binding sites, and comparison with published data on the histidine content of glycinin suggests that the majority of these residues are on the surface of the protein. Denaturation by 6 M urea increased the number of binding sites to 330. The number of zinc binding sites was found to vary with the protein concentration in 0.5 M KCl. The affinity of zinc for the protein varied with the protein concentration. Increasing the KCl concentration to 1.0 M decreased the affinity of zinc for the protein and increased the number of binding sites. Zinc preferentially binds to EDTA rather than to glycinin. Binding at pH 5.5 resulted in a reduction in the number of binding sites to 23. Ultracentrifugal analysis of glycinin in the presence and absence of zinc gave S_{20, W} values of 13.1 and 11.1, respectively. Calcium and magnesium did not bind to glycinin in 0.5 M KCl at pH 6.2.     

Filamentous structures of bovine myosin in diluted suspensions and gels

Turbid solutions and fine-stranded gels of myosin from bovine semi-membranous muscle were investigated by transmission and scanning electron microscopy. Evidence is given that the turbidity was caused by filament formation upon dialysis to pH 5.5 and 0.25 M KCl and to pH 4.0 and 0.6 m KCl at 4°C. The filaments formed at pH5.5 and 0.25 m KCl had a backbone with a diameter of c. 25 nm with the myosin heads located close to the filament backbone. The total width of these filaments was c.45nm. The filaments were prepared for electron microscopy by adsorption on various substrates, negative staining, or freeze drying and rotary shadowing. Variations in the preparation technique did not affect the appearance of the filaments. The filaments formed at pH 4.0 and 0.6 m KCl had a more irregular appearance, and the total filament width varied between 20 and 45 nm. Fringes of globular material surrounding the filament backbone were seen but also clusters of myosin molecules protruding further out from the backbone and from the filament ends. Comparison of heat-treated filaments in dilute solutions with strands of the gel network confirmed that the gel strands originated from filaments formed upon dialysis prior to gelation. Typical features of the network structure were junction zones formed by parallel alignments of filaments in pairs and by end-to-side interactions forming so-called Y-junctions. At pH5.5 and 0.25 m KCl these interactions resulted in a rather loose and open network structure. At pH 4.0 and 0.6 M KCl the filaments often interacted approximately at right angles, which resulted in a denser network than that observed atpH5.5 and 0.25 m KCl. The efficient network formation at pH 4.0 gave rise to spontaneous gel formation upon dialysis without any heat treatment. Additional heating did not change the character of the network, and no differences could be observed between unheated and heat-treated gels at low magnifications. At higher magnifications it could be seen that heating resulted in loss of details of the filaments at both pH values and ionic strengths. The shape of the myosin heads was lost, and the heads fused together on the filament backbone.     

Microstructural features of composite whey protein/polysaccharide gels characterized at different length scales

Mixed biopolymer gels are often used to model semi-solid food products. Understanding of their functional properties requires knowledge about structural elements composing these systems at various length scales. This study has been focused on investigating the structural features of mixed cold-set gels consisting of whey protein isolate and different polysaccharides at different length scales by using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Whey protein cold-set gels were prepared at different concentrations to emulate stiffness of various semi-solid foods. Mixed gels contained different concentrations of gellan gum, high methyl pectin or locust bean gum. Results obtained with CLSM, at the micrometer length scale, indicated the homogeneous nature of the investigated gels. Results obtained with SEM, at the sub-micron length scale, indicated the presence of spherical protein aggregates. During the gel preparation (acidification), the presence of polysaccharides in the whey protein gels led to on initially segragative phase separation into a gelled protein phase and a polysaccharide/serum phase at a micrometer length scale. At the final pH of the gels (pH 4.8, i.e. below the pI of whey proteins), the negatively charged polysaccharides interacted with the protein phase and their spatial distribution was effected by charge density. Polysaccharides with a higher charge density were more homogeneously distributed within the protein phase. Neutral polysaccharide, locust bean gum, did not interact with the protein aggregates but was present in the serum phase. Using SEM, a new type of microstructure formed in the whey protein/polysaccharide gels was characterized. It composed of a protein continuous, porous network at the length scale of 100 μm, coexisting next to the pools of serum which contained spherical protein-rich domains. Heterogeneity of the structure strongly related to the macroscopic behavior of the gels under large deformation. Upon uniaxial compression these heterogeneous gels releases a large amount of serum. Combination of the results of two microscopic techniques, CLSM and SEM, appeared to offer unique possibilities to characterize the structural elements of whey protein/polysaccharide cold-set gels over a wide range of length scales.     

Formation of two types of gels from bovine myosin

Myosin was isolated from bovine m. semimembranosus and gels were formed by heat treatment at different pH values and ionic strengths. The gels were subjected to rigidity measurements and their microstructure was studied by scanning electron microscopy. This article provides evidence that myosin can form two completely different gel structures in the pH range 5.5–6.0, depending on ionic strength. Fine stranded gel structures were formed at low ionic strength (0.25M KCl), whereas coarsely aggregated gel structures were formed at high ionic strength (0.6M KCl). The fine stranded structure had a higher rigidity than the coarsely aggregated structure. It was found that all fine strand myosin gels were formed from turbid solutions and the aggregate gels from clear solutions. When the pH was lowered to 4 in 0.6M KCl a strand-type gel structure formed spontaneously on dialysis, even without heat treatment. This structure did not change in character on heating. It was concluded that the conditions required for the formation of strand-type myosin gels were already present before the heat treatment and that the strands were made up of myosin filaments at certain pH and ionic strength combinations, which produced a turbid solution. The strand-type structures were considered specific with regard to myosin interactions which was not the case for the aggregated structures. Variation of the heating temperature in the range 55 to 65°C had no major effect on the type of structure formed.     

Calcium sulphate‐induced soya bean protein tofu‐type gels: influence of denaturation and particle size

Soya bean protein isolate (SPI) dispersions (7.25%, w/v) were heated at 65, 75, 85 or 90 °C for different time periods to produce SPI aggregates with diverse degrees of denaturation and particle size to investigate the effects on calcium sulphate (CaSO₄)‐induced tofu‐type gel. The results revealed that gel hardness and water‐holding capacity correlated positively with the degree of denaturation of glycinin (11S) and the particle size of the SPI aggregates. The formed gels showed more uniform and denser network structures with increasing degrees of denaturation and particle size of SPI. Hydrophobic interaction was speculated to be the crucial factor for the retention of gels prepared by SPI whose degree of denaturation by 11S was lower than 4.35%. However, disulphide bonds probably played a more important role in the retention of gels generated by SPI with the 11S denaturation degree of >84.47%. Moreover, the bulk density of the protein aggregates might determine the gel structures to a certain extent.     

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。     

伴大豆球蛋白胃蛋白酶水解产物中促双歧杆菌增殖肽的分离和鉴定

大豆贮藏蛋白主要包括大豆球蛋白(Glycinin)和伴大豆球蛋白(Conglycinin),本研究采用Sephadex-G15凝胶过滤和薄层层析的方法,对伴大豆球蛋白胃蛋白酶水解产物中促双歧杆菌增殖肽进行分离,所得活性组分通过毛细管HPLC及质谱进行鉴定,结果表明,分离得到促双歧杆菌增殖活性最强的组分是由性质相近的肽混合物组成,通过毛细管HPLC可以得到活性酶解肽的图谱,并通过质谱可知酶解肽主要由6-10个氨基酸残基组成。上述结果提示,伴大豆球蛋白中的生物活性物质是以无活性的形式存在于蛋白质的多肽链中,必须通过适当酶解,在一定条件下才能释放出来,发挥出各种生物学功能。     

Characterisation of polyclonal and monoclonal antibodies against glycinin (11S storage protein) from soya (Glycine max)

Polyclonal and monoclonal antibodies have been raised against the soya (Glycine max L) 11S storage protein, glycinin. The characteristics of the antibodies have been studied using enzyme-linked immunosorbent assay (ELISA) and immunoblotting techniques. The polyclonal antibodies showed strong recognition of the storage proteins from pea, and smaller but significant interactions with storage proteins from other seeds. Two monoclonal antibodies were virtually completely soya specific, recognising different continuous epitopes from the acidic polypeptides believed to be present on the surface of the native protein. A third monoclonal showed a much wider specificity in the ELISA, including the recognition of certain storage proteins from other seed types to a greater extent than soya. The epitope for this antibody may have been present on the surface of the native protein and was discontinuous, dependent on spatial organisation for recognition.     

Thermally treated soya bean oleosomes: the changes in their stability and associated proteins

Oleosomes are subcellular organelles present naturally in plant seeds for storing lipids. Oleosomes can be used in the preparation of various food products, such as creams, salad dressings, mayonnaise and emulsion. However, food products are always subjected to thermal processing, and therefore, the evaluation of the thermal stability of oleosomes is of great important. The present work aimed to understand the effect of soya bean oleosome-associated proteins (SOAPs) on the thermal stability of soya bean oleosome emulsion (SOE). SOE was thermally treated for 15 min at different temperatures of 65, 75, 85 and 95 °C. The confocal laser scanning microscope (CLSM) and Cryo-SEM of SOE, and as well as fluorescence spectroscopy, circular dichroism of SOAPs were investigated. The stability of SOE was significantly affected by thermal treatments, by modulating the conformational structures of SOAPs, while the composition changed slightly. The results of particle size, zeta potential and CLSM showed that thermal treatments caused aggregations of oleosomes especially at high temperatures (75–95 °C). Thermally treated oleosomes were observed to have a rough surface. Results of this work are useful for understanding the underlying mechanisms of SOAPs in maintaining the thermal stability of SOE.     

Effects of β‐glucans on properties of soya bean protein isolate thermal gels

The effects of concentration and molecular weight of oat β‐glucans on properties of soya bean protein isolate (SPI) thermal gels prepared by heating at 90℃for 30 min were investigated. Compared with control (free of β‐glucan) formulations, the presence of β‐glucans (0.5–1.5%, w/v) largely enhanced storage modulus (G′) and texture properties of SPI (12%, w/v) thermal gels measured by dynamic oscillatory rheometry and texture profile analysis, which were developed as increasing β‐glucan concentration and molecular weight. It is possible that β‐glucans could cause the formation of protein aggregates to produce gels through hydrophobic interactions. Mixed gel systems at low ionic strength showed higher G′ resulting from the lower denaturation temperature of SPI, which was beneficial to the formation of gel structure. In addition, although adding a certain amount of β‐glucan into SPI reduced water‐holding capacity of mixed gels, high molecular weight of β‐glucan improved their water‐holding capacity compared to control formulations attributed to the improvement of the structural integrity of the mixed gel network.     

Microencapsulation of flaxseed oil by soya proteins–gum arabic complex coacervation

Application of soya proteins (SP) in flaxseed oil microencapsulation based on complex coacervation was investigated. The effects of SP/gum arabic (GA) mixing ratio (1:2, 1:1 and 2:1) and pH (2.80, 3.15 and 3.75) on coacervate preparation were studied firstly. The highest coacervate yields (CY) were achieved at SP/GA = 1:1, pH 3.15, and SP/GA = 2:1, pH 3.75, which were 81.2 ± 2.0%, 88.1 ± 0.6%, respectively. Thereafter, the microencapsulation of flaxseed oil was detected in accordance with the results of the coacervation of SP/GA, that is the optimal condition for microencapsulation was corresponded to the condition where CY was the highest. Under the conditions of SP/GA = 1:1, pH 3.15, and SP/GA = 2:1, pH 3.75, the microencapsulation efficiency and total yield reached 81.5 ± 0.1% and 81.7 ± 0.4%, and 77.4 ± 3.7% and 86.7 ± 2.4%, respectively. Microscopic morphology revealed that the formation of a biopolymer shell around the oil droplets was achieved at specific conditions.     

Microstructure of suwari and kamaboko sardine surimi gels

In a previous work it was suggested that the texture of kamaboko (set and cooked) gels made from sardine surimi under varying setting conditions was predetermined by the specific matrix forming in each suwari (set) gel. This paper describes the microstructure of the networks formed in suwari and kamaboko gels set at 25, 35 and 40 °C for 30 or 60 min as examined by scanning electron microscopy (SEM). Cooking conditions for kamaboko gels were fixed at 90 °C for 30 min; other preparation conditions were invariable. At low magnification (≤×500) the gel matrixes were compact, with practically no differences among lots. At higher magnification (×20 000), the suwari gel matrixes formed at low temperature consisted of globules. At higher temperatures the globules joined up to form fibrillar structures (fibres) and zones of disordered globule aggregation (coagula); at longer setting times, lateral bonding of the fibres became apparent. Kamaboko gels produced from unstructured globular matrixes exhibited only a few fibrillar zones and large areas of coagula. Where there was already an incipient fibrous formation, these developed into individual fibres or bundles of fibres that correlated with the best texture characteristics. Suwari gels with extensive lateral bonded fibres gave rise to kamaboko gels with a highly compact appearance under SEM; this correlated with a decline in texture values. These different structures suggest that the protein–protein bonds in the suwari networks have different levels of stability to heat, and these levels determine whether or not the proteins can subsequently be reorganised when the kamaboko gel forms. © 1999 Society of Chemical Industry     

Properties of soya milk and tofu prepared with γ-irradiated soya beans

Soya beans (Glycine max) ‘hwang keum’ were γ-irradiated at dose levels of 0, 2.5, 5, 10 and 20 kGy and the effects of the irradiated soya beans on soya milk and tofu properties were studied. An irradiation dose of 5 kGy caused an increase in yield of soya milk and tofu while having very little effect on their quality. The properties of tofu prepared with the soya beans irradiated at 2.5–5 kGy showed no significant difference from the non-irradiated control. However, at higher doses (10–20 kGy), decreases in yield, water holding capacity and sag value of tofu were observed. Compared with the non-irradiated control, hardness and fracturability in the texture of tofu were both significantly increased when the soya bean had been irradiated at 10–20 kGy, while cohesiveness and adhesiveness decreased. The changes in color values of soya milk and tofu were pronounced at 20 kGy.     

大豆制品的产业化进展

本文以大豆的化学组成为出发点，讨论大豆制品的加工工艺和产业化进展。比较了近代大豆制品和中国传统大豆制品的加工工艺，提出了大豆制品产业化的途径。     

Enzymic analysis of soya beans lacking lipoxygenases

The homozygous inheritance of recessive alleles for lipoxygenase, -L₁, -L₂ and -L₃ incorporated into a commercial soya bean seed line, IAC 8, was evaluated. The activity of each isozyme, determined by spectrophotometry demonstrated a very low activity for the mutant -L₁ and respective progeny and a low activity for -L₂, -L₃ and their progenies. The methodology employed was shown to be a reliable and rapid method when evaluating lipoxygenase from crops.     

The use of anti‐soya globulin antisera in investigating soya digestion in vivo

Polyclonal antisera have been developed which recognise the soya globulins glycinin and β‐conglycinin. Their binding to proteolysed and processed globulins has been characterised with a view to using the antisera as probes to investigate the fate of soya globulins during digestion. Trypsinolysis reduced the immunoreactivity of β‐conglycinin but increased that of glycinin by threefold, as determined by enzyme‐linked immunosorbent assay (ELISA). However, both antisera recognised trypsinolysis products poorly by immunoblotting. These data are consistent with the fact that the anti‐glycinin antiserum was raised to digested glycinin and would therefore recognise both intact and proteolytic intermediates of glycinin. The latter would be disrupted into component polypeptides by sodium dodecyl sulphate–polyacrylamide gel electrophoresis and hence would only be present in the ELISA and not after blotting. The antibody preparations were used to investigate the fate of soya globulins during in vivo digestion of a processed soya ingredient in rats. Both glycinin and β‐conglycinin were digested rapidly, intact globulins disappearing from the gastrointestinal tract 3 h after dosing. Immunoreactive globulins were found in gut contents and associated with gut tissues but appeared to be in a semi‐intact form, probably comprising proteolytic intermediates. This study demonstrates the usefulness of antibody methods in following the digestion of individual components in a complex mixture, such as is found in food. The availability of antibody preparations which recognise heat‐stable epitopes will open the way for investigations into the effects of pre‐treatments, such as cooking, which are pertinent to human consumption of legumes. © 2000 Society of Chemical Industry     

The effects of ultra-high-pressure treatments combined with heat treatments on the antigenicity and structure of soy glycinin

Glycinin is one of the important allergens found in soybeans, which can potentially cause severe allergic reactions. Therefore, reducing the antigenicity of glycinin is of major significance to the research of soybean allergies. In order to detect the relationships between the antigenicity and structure of glycinin, samples were extracted from defatted soybean and then processed by ultra-high-pressure combined heat treatments. The processed proteins were determined using SDS-PAGE, enzyme-linked immunosorbent assay (ELISA), immunoblotting, exogenous fluorescence, free sulfhydryl groups and Fourier transform methods. The results revealed that the antigenicity of the processed soy glycinin had decreased. In addition, the content levels of the hydrophobic groups, free sulfhydryl groups, α-helix, β-turn and random coils had increased, and the content of β-sheets had decreased. The results indicated that the reduction in the antigenicity of the glycinin was due to the processing treatments, which effectively destroyed the spatial structure of the glycinin.     

Total inactivation of lipoxygenase in whole soya bean by pulsed light and the effect of pulsed light on the chemical properties of soya milk produced from the treated soya beans

The inactivation of lipoxygenase (LOX) in the whole soya bean prevents lipid oxidation that produces an off‐flavour of soya food. The inactivation of lipoxygenase in the whole soya bean by pulsed light (PL) was examined with three distances (5, 7 and 9 cm) from the PL strobe and for different durations. Soya bean was treated with PL with and without ice surrounding the soya bean sample tray for limiting the rise in sample temperature. Results show that without ice surrounding the sample tray, the lowest LOX residual activity was 4.7%, 0.4% and 0.0% for 80‐s duration at 5 cm distance from the PL strobe, 110 s at 7 cm from the strobe and 150 s at 9 cm from the strobe, respectively; the soya bean temperature after treatment was 109.6, 116.3 and 114.8 °C, respectively. The instantaneous temperatures of the soya bean core measured during PL operating were above 100 °C. The lipoxygenase band was disappeared after longest PL treatments of each distance compared with the LOX band control as assessed by electrophoresis. The pulsed light had no negative effect on peroxide value of produced soya milk. However, PL reduced significantly the total solid amount and changed the colour of the produced soya milk. The residual activity with sample cooling by ice during treatment was 79.0%, 98.8% and 95.7%, with sample temperatures of 81.7, 91.2 and 66.9 °C, respectively. This study indicates that PL illumination could fully inactivate LOX in whole soya beans, with the photo‐thermal effect of PL as the main factor responsible for the inactivation of LOX.