不同酸碱体系中绿豆蛋白功能及构象

探讨了不同酸碱体系中绿豆分离蛋白、清蛋白和球蛋白的构象和溶解度、乳化性、乳化稳定性。结果表明:绿豆分离蛋白、清蛋白和球蛋白在酸性体系中溶解度、乳化性和乳化稳定性较低,随着pH的升高其功能特性随之升高;绿豆分离蛋白的α-螺旋结构在接近等电点时较低,随着pH的升高,α-螺旋结构升高,β-折叠结构和无规则卷曲结构含量随pH的增大而降低;绿豆球蛋白在碱性体系中,β-折叠结构和无规则卷曲结构的含量呈现先降低后升高的趋势,β-转角结构的含量呈现先升高后降低的趋势;绿豆清蛋白在酸性条件下的α-螺旋结构含量、β-转角结构和无规则卷曲结构较高,随着pH值的升高,β-转角结构逐渐向的α-螺旋、β-折叠、无规则卷曲等结构变化;在不同酸碱体系中绿豆蛋白的空间构象不同,造成各条件下所暴露的基团不同,进而影响绿豆蛋白的功能特性。这为绿豆蛋白加工利用过程中功能特性变化规律研究提供可靠的理论依据。     

大豆11S球蛋白凝胶形成的影响因素分析

以低温脱脂大豆粕为原料,采用等电点冷沉法浸提11S球蛋白。对11S球蛋白凝胶形成过程中影响凝胶质构的因素进行了分析,研究表明,11S球蛋白凝胶形成时蛋白浓度、加热温度、加热时间、蛋白溶液pH对凝胶质构均有一定的影响。采用正交实验设计,通过质构仪进行物性测定比较其凝胶性,大豆11S球蛋白浓度14%、加热温度90℃、溶液pH为7、加热时间60min条件下形成的凝胶强度最好,其凝胶面积410.30g·s,凝胶力117.9g。     

大豆球蛋白自组装聚集及凝胶特性

研究了在低pH值、低离子强度下,分别加热诱导不同浓度11S(大豆球蛋白)和7S(大豆伴球蛋白)自组装纤维化聚集体的形成。通过平均粒径和Thioflavin T(硫磺素T)荧光光谱,对自组装纤维化聚集体的性质进行表征,并对其热致凝胶的流变学,硬度和微结构特性进行考察。结果表明:在低pH值、低离子强度的诱导条件下,蛋白浓度对自组装聚集的形成起着关键作用,随着诱导浓度的增大,蛋白的纤维化聚集越明显,7S比11S更容易形成纤维化聚集。在酸性环境下,大豆球蛋白的纤维化聚集程度越高,越有利于热致凝胶网络结构的形成。在相同的预处理条件下,11S自组装凝胶硬度强于7S。扫描电镜结果显示7S自组装凝胶的网络结构较11S致密,但有序性较11S低。     

高浓度魔芋葡苷聚糖与大豆分离蛋白混合凝胶质地特性研究

研究了不同处理条件和试剂对高浓度魔芋葡苷聚糖与大豆分离蛋白混合凝胶质构特性的影响，并进行了凝胶的扫描电子显微镜观察。结果表明，KGM与SPI混合物在体系pH值为9、温度90℃下加热40min时，其形成的凝胶强度和弹性较好。凝胶微观结构的扫描图片分析表明，高浓度下KGM与SPI混合物在水溶液和碱性条件下均能形成较好的凝胶网络结构，而且不同配比和不同处理样品所形成的凝胶体的微观结构差异较大。     

pH值对大豆11S球蛋白结构和表面疏水性的影响

采用Lowry法、8-苯氨基萘-1-磺酸铵盐（8-anilinonaphthalene-1-sulfonic acid ammonium salt,ANS）荧光探针法研究pH值对大豆11S球蛋白的溶解性和表面疏水性的影响,并利用圆二色光谱和荧光光谱对不同pH值条件下11S球蛋白二级结构和三级结构进行分析,为研究大豆蛋白结构与表面疏水性之间的构效关系提供理论基础。结果表明：除等电点外,大豆11S球蛋白溶解性和表面疏水性呈负相关,并且随着pH值的升高,大豆球蛋白二级结构中发生β-折叠和无规卷曲向α-螺旋的转变,三级结构中色氨酸（Trp）残基微环境极性降低。大豆球蛋白的表面疏水性与α-螺旋结构含量呈负相关。     

大豆球蛋白的纤维聚集体行为及其稳定性研究

为了明确蛋白质的纤维聚集行为,本研究以大豆球蛋白(soy globulin,11S)为原料,从亚基层面对酸性条件下热诱导的11S纤维聚集过程进行跟踪,监测蛋白及其亚基的水解过程、结构变化及其稳定性。结果表明,11S的纤维化是一个多步骤的过程,包括多肽链的水解、自组装成淀粉样纤维聚集结构及逐渐生长成宏观可见的具有扭曲螺旋结构的纤维聚集体。与11S纤维化过程的单指数增长相比,酸性亚基的纤维化过程存在迟滞期。酸性亚基在纤维化聚集的初期主要贡献于纤维聚集的成核过程,碱性亚基的加入改变其纤维聚集进程。蛋白质的纤维化过程会增加11S在等电点处的溶解度,降低中性和酸性pH下的溶解度。此外,碱性环境(pH值10.0)会导致11S纤维聚集体全部溶解、宏观纤维长度变小、结构发生改变。以上研究结果旨在为合理利用蛋白纤维化聚集体作为新的功能性食品配料提供理论依据。     

低pH对燕麦球蛋白热致凝胶和分子结构的影响

在酸性条件下制备出了燕麦球蛋白热致凝胶。利用流变仪、低场核磁共振仪和扫描电镜研究了不同pH时燕麦球蛋白热致凝胶的粘弹性与微观结构。同时利用紫外和荧光光谱法研究了在加热条件下pH对溶液中燕麦球蛋白分子结构的影响。由凝胶的流变学结果可知,在一定的酸性范围内,凝胶的弹性模量G'会随着pH的减小而增大。水分弛豫特性和扫描电镜结果显示,随着pH的减小,热致凝胶逐渐由致密的球状聚集结构转变为交联的网络结构。紫外吸收和荧光发射光谱表明,低pH导致了燕麦球蛋白分子的变性和内部疏水性氨基酸的暴露。总而言之,在低pH条件下,部分变性的燕麦球蛋白经热处理后,会聚集形成紧密堆积或疏松的凝胶结构。     

L-精氨酸/L-赖氨酸对乳清蛋白凝胶质构和持水性的影响

为考察L-精氨酸/L-赖氨酸及pH对乳清蛋白结构和凝胶性质的影响,研究2种碱性氨基酸对乳清蛋白热诱导凝胶质构及持水性的影响。研究表明,L-精氨酸/L-赖氨酸对蛋白聚集体大小及ζ-电位(pH 2.0下L-精氨酸处理除外)有降低的趋势;紫外、荧光光谱显示在酸性条件下,碱性氨基酸促进蛋白分子结构展开,而在碱性条件下则使蛋白结构倾向折叠。不同pH(2.0、5.2、7.59、9.74和10.76)的蛋白溶液,每个pH的样品分别含有质量浓度1、3 g/L L-精氨酸或L-赖氨酸,90℃加热30 min后能够形成颜色随pH变化而变化的凝胶。化学作用力分析则显示2种氨基酸通过改变蛋白分子间作用而显著改变质构特性和持水性。总之,在pH对蛋白结构和凝胶功能性影响的基础上,L-精氨酸/L-赖氨酸能够进一步提高凝胶质构特性与持水性。     

碱性条件下大豆11S球蛋白溶液的性质和分子结构

对碱性条件下大豆11S球蛋白溶解性、表面疏水性(H0)、Zeta电位、粒径以及分子结构进行研究。当pH值由7.0增加到12.0时,大豆11S球蛋白的溶解性增加,H0降低,Zeta电位的绝对值增大,平均粒径降低,这表明碱性条件下大豆球蛋白表面负电荷增多,通过静电排斥作用减少了蛋白质聚集,促进蛋白质溶解,更多的极性氨基酸暴露于蛋白质表面可能会导致H0降低。此外,随着pH值的升高,α-螺旋含量增加,无规卷曲含量降低,蛋白分子中的酪氨酸和色氨酸残基趋于"包埋"态。碱性条件下大豆11S球蛋白的二硫键构型发生改变,说明可能发生蛋白质亚基的解离和聚合。     

棉籽球蛋白凝胶特性研究

该研究以棉籽球蛋白为原料,考察了棉籽球蛋白溶解度随pH的变化,并于中性条件下加热诱导棉籽球蛋白聚集形成凝胶。采用物性仪对不同条件下制备的凝胶质构特性进行研究。通过正交试验考察蛋白质浓度、pH、加热温度、加热时间对凝胶形成的影响,得出形成凝胶较为适宜的条件。     

Viscoelastic properties and microstructures of 11S globulin and soybean protein isolate gels: Magnesium chloride-induced gels

Heat-induced gels of 11S globulin (11S) or soybean protein isolate (SPI) were prepared using magnesium chloride (MgCl₂) as a coagulant. Viscoelastic properties and microstructures of 11S and SPI gels were quantified using dynamic viscoelastic measurement (DVM) and confocal laser scanning microscopy (CLSM). The addition of sodium chloride was necessary for 11S and SPI to form MgCl₂-induced gels. DVM indicated that 11S formed stiffer and more solid gels than SPI under all experimental conditions. CLSM showed that the microstructures of 11S gels were coarser and more heterogeneous than SPI gels in comparable conditions. The microstructures of 11S gels were highly affected by MgCl₂ concentration whereas those of SPI gels were relatively insensitive to MgCl₂ concentration. The microstructures of 11S and SPI gels were analyzed by two parameters: the fractal dimension and the average density of gel networks. Compared to SPI, 11S forms MgCl₂-induced gels with a lower fractal dimension and a higher density of network structures.     

发芽对大豆蛋白凝胶性质的影响

研究了发芽大豆蛋白质凝胶性质的变化。采用碱提酸沉法制备大豆分离蛋白(SPI),以葡萄糖酸-δ-内酯(GDL)为凝固剂制备大豆蛋白凝胶,系统研究了不同芽长大豆蛋白凝胶强度的变化。通过SDS-聚丙烯酰胺凝胶电泳(SDS-PAGE)图谱分析了发芽过程中SPI的变化及其对大豆凝胶强度的影响。结果发现:SPI中7S球蛋白的α'、α亚基和11S球蛋白的酸性亚基A3、A发芽时发生明显降解,但11S球蛋白各亚基在发芽初期变化小,利于大豆蛋白质分子之间形成网络结构使凝胶强度增强。随着发芽时间的延长,11S球蛋白也部分发生降解,凝胶强度下降。     

Structural Characterization of Amaranth Protein Gels

ABSTRACT: Gelation capacity of a native amaranth protein isolate was studied. Structural properties of gels prepared at different protein concentration and heating conditions were analyzed. Proteins present in amaranth isolates obtained by water extraction at pH 9.0 and subsequent isoelectric precipitation are able to form gels of yellowish appearance. Gel color intensity increased while luminosity decreased with increasing protein concentrations. High protein concentration allowed the formation of matrices with high water-holding capacity. In addition, increasing the heating temperature resulted in gels of high luminosity and low water-holding capacity. The increase of protein concentration (10% to 20% w/v) as well as the increase of heating temperature (70°C to 95°C) and heating time (10 to 30 min) resulted in the formation of a more ordered matrix with smaller pores, mainly stabilized by disulfide bonds and, at a lower extent, by noncovalent interactions (specially hydrogen bonds and hydrophobic interactions). Both amaranth globulin (11S globulin and P globulin) participated in gel structure via high-molecular-weight aggregates (>100 kD). Gel structure was stabilized via noncovalent bonds by monomer species of 42 kD and those of molecular mass lower than 20 kD localized in the interstitial spaces of gel matrix.     

Forces Involved in Soy Protein Gelation: Effects of Various Reagents on the Formation, Hardness and Solubility of Heat-Induced Gels Made from 7S, 11S, and Soy Isolate

The effects of various reagents on the formation, hardness and solubility of heat-induced gels of soybean 7S, 11S globulins and isolate were studied. Gels were formed in 30 mM Tris HCl buffer (pH 8.0) with or without reagents by heating at 80°C for 30 min. The results indicated that electrostatic interactions and disulfide bonds are involved in the formation of 11S globulin gels; mostly hydrogen bonding in 7S globulin gels and hydrogen bonding and hydrophobic interactions in soy isolate gels. Analyses of the proteins solubilized from the gels indicated that the basic subunits of 11S globulin interact with 7S globulin in soy isolate gels. The contribution of certain acidic subunits to network formation in US soy isolate gels is limited     

Effects of combined high-pressure and heat treatment on the textural properties of soya gels

SPI, 7S, and 11S globulin at 12% (w/v) protein concentration, at neutral pH, did not form gels when heat-treated (90 °C, 15 min) or when high pressure-treated (300–700 MPa), except for the 11S, which formed a gel when heat-treated. The combination of heat and pressure (that is heating the solutions in a water bath and then pressure-treating at room temperature or the reverse sequence), led to differences: when heat-treatment was before high-pressure treatment, only the 11S fraction formed a self-standing gel; however, when the solutions were pressurised before heat treatment, all the proteins formed self-standing gels. The textural and water-holding properties were measured on the gels formed with the three different soy proteins.     

Complex coacervation of chitosan and soy globulins in aqueous solution: a electrophoretic mobility and light scattering study

The effect of pHs and heating on the protein–polysaccharide complexation between the 0.5 wt% soy globulin (7S or 11S) and 0.1 wt% chitosan was studied. Electrophoretic and light scattering techniques were used to examine the electrical charge and aggregation of the individual biopolymers and complexes. At pH 3.0–6.5, 7S (or 11S) globulin in the presence of chitosan had significantly higher ζ‐potentials and lower particles size than 7S (or 11S) globulin alone did (e.g. 600–6000 nm at pH 5.5), indicating the formation of complexes. After heating 7S (or 11S)–chitosan mixtures had higher positive value of ζ‐potential. 7S (or 11S)–chitosan mixtures exhibited a significant increase in positive value of ζ‐potential and stability after heating at lower pH values (pH 3.3 instead of pH 4.5). Compared with other mixtures, at pH 2.5–6.0, the most remarkable decrease in aggregation was obtained for 11S–chitosan mixtures after heating at pH 3.3.     

The Young's Modulus,Fracture Stress,and Fracture Strain of Gellan Hydrogels Filled with Whey Protein Microparticles

Texture modifying abilities of whey protein microparticles are expected to be dependent on pH during heat‐induced aggregation of whey protein in the microparticulation process. Therefore, whey protein microparticles were prepared at either pH 5.5 or 6.8 and their effects on small and large deformation properties of gellan gels containing whey protein microparticles as fillers were investigated. The majority of whey protein microparticles had diameters around 2 μm. Atomic force microscopy images showed that whey protein microparticles prepared at pH 6.8 partially collapsed and flatted by air‐drying, while those prepared at pH 5.5 did not. The Young's modulus of filled gels adjusted to pH 5.5 decreased by the addition of whey protein microparticles, while those of filled gels adjusted to pH 6.8 increased with increasing volume fraction of filler particles. These results suggest that filler particles were weakly bonded to gel matrices at pH 5.5 but strongly at pH 6.8. Whey protein microparticles prepared at pH 5.5 showed more enhanced increases in the Young's modulus than those prepared at pH 6.8 at volume fractions between 0.2 and 0.4, indicating that microparticles prepared at pH 5.5 were mechanically stronger. The fracture stress of filled gels showed trends somewhat similar to those of the Young's modulus, while their fracture strains decreased by the addition of whey protein microparticles in all examined conditions, indicating that the primary effect of these filler particles was to enhance the brittleness of filled gels.     

Composition, solubility and gel properties of salt soluble proteins from two bovine muscle types

The composition, pH solubility profile and thermal gelation behavior of two bovine muscles, vastus intermedius (VI, predominately red fibers) and semimembranosus (SM, predominantly white fibers) were compared. VI had a higher fat content and pH and lower protein content than SM. Between pH 5.2 and 5.8, the salt soluble proteins (SSP) from SM were more soluble than those from VI at the same pH, whereas solubilities above pH 6.0 were similar. Properties of SSP gels were measured at pH 5.5 and 6.1, the ultimate pH for SM and VI, respectively. Water lost from the VI gels due to syneresis was about 3 times greater than that lost from SM gels. VI gels prepared at pH 5.5 were firmer (p<0.05) than at pH 6.1, whereas deformability of SM gels at pH 6.1 were greater (p<0.05) than at pH 5.5. No differences (p>0.05) were observed between the firmness or deformability of VI or SM gels when compared at the same pH. Results suggest that ultimate muscle pH and fiber type do influence the properties of bovine SSP gels, although the effect is not as great as that previously reported for poultry muscle proteins.     

豌豆蛋白的功能特性研究

本论文对豌豆球蛋白(7S、11S)和豌豆分离蛋白(PPI)的物化和功能特性进行了分析和比较。结果表明,豌豆球蛋白具有良好的功能特性,其溶解度(PS)、乳化能力、乳化稳定性均显著高于PPI。荧光光谱和表面疏水性(H0)分析表明,PPI是部分变性的蛋白,其制备过程中的酸碱处理导致蛋白分子伸展、H0增加。DSC表明,11S热稳定性比7S要高,豌豆分离蛋白和豌豆7S出现不同程度的蛋白变性。     

L-组氨酸修饰乳清蛋白结构及其热诱导凝胶特性

采用L-组氨酸（L-His）作为蛋白凝胶功能性的增强剂,将其加入乳清分离蛋白溶液中制备热诱导凝胶,研究L-His对乳清蛋白结构及其凝胶特性的影响。结果表明：在乳清蛋白等电点（pI 5.2）时蛋白形成尺度约1 700 nm、具有极小比表面积且几乎不带电的蛋白聚集体,远离蛋白等电点时则所形成的聚集体大小约为400 nm;L-His抑制蛋白聚集体的形成而减小粒径、显著提高聚集体比表面积,促进蛋白分子结构展开并提高其带电量。在经历热诱导后,乳清蛋白在其等电点时形成持水性差的白色凝胶,而在其他pH值时则形成持水性高的黄色凝胶且越远离等电点,胶体黄度值越大;L-His的加入对凝胶颜色变化无显著影响,但能够显著提高凝胶的持水性（P＜0.05）;有效提高凝胶的质地特性,特别是在pH 7.59和pH 9.74时显著提高乳清蛋白凝胶的弹性及咀嚼性（P＜0.05）。这些质构变化可能主要归结于L-His改变了凝胶内的氢键、二硫键和疏水作用力的重排。总之,L-His修饰乳清蛋白结构而改变其凝胶性能且同时受到pH值的影响。