Analysis of vicilin (7S)‐class globulin in cocoa cotyledons from various genetic origins

Cocoa cotyledons contain vicilin (7S)‐class globulin (VCG), a major storage protein. It is the native source of oligopeptides and free amino acids which have been identified as precursors of cocoa‐specific aroma and are formed through proteolysis during fermentation. High‐resolution electrophoresis of native proteins isolated from ripe, unfermented cocoa cotyledons harvested from different cultivars was used to determine genetic differences of the genotypes. Flavour differences have been reported to exist after standard fermentation in cocoa beans harvested from various genotypes. In this paper, SDS‐PAGE and 2D IEF/SDS‐PAGE polypeptide separation patterns are shown which were separately isolated from cotyledons of various genetic origins. Cotyledons from three cultivars belonging to genetically distant varieties and a hybrid, Criollo, Forastero and Trinitario, did not reveal any analytical identity differences of VCG subunit polypeptide bands. Additionally, proteins of cotyledons harvested from three of those clones which were reported to produce genotype‐specific flavour differences in raw cocoa after standard fermentation, SCA 12, UIT1 and PBC 140, when analysed in the same way, did not indicate differences. Thus the cotyledon storage proteins from various genetically different cocoa trees are, within methodological limits, the same. We conclude that aroma differences in raw cocoa harvested from various genotypes are the result of other genetic, physiological or curing‐related factors, but are not due to genetic differences of aroma precursors derived from storage proteins. © 2002 Society of Chemical Industry     

分子力对大豆蛋白透明凝胶作用机理研究

通过对大豆分离蛋白/大豆7S球蛋白凝胶光学和流变学性质与溶剂、牛血清白蛋白、脂肪酸盐浓度关系的深入研究,探讨了分子力对大豆蛋白透明凝胶的作用机理．结果表明氢键、静电力和疏水作用对大豆蛋白透明凝胶的形成具有重要的影响．这为进一步研究大豆蛋白凝胶的光学性质和研制透明的大豆蛋白产品提供理论依据．     

长白山核桃球蛋白的提取、分离纯化及其功能性质研究

球蛋白是长白山核桃(Juglans mandshurica Maxim)种仁贮藏蛋白主要组分之一,也是深度开发和利用核桃蛋白资源深加工产品的主要成分。在采用改进的Osborne法提取核桃球蛋白并通过离子交换层析纯化球蛋白的基础上,初步研究其结构特性后,将其功能性质与大豆分离蛋白做对比,进行全面分析,为其在食品加工中的应用提供理论依据。结果表明:制备的球蛋白含量为80.71%,阴离子交换层析图谱出现4个峰,经SDS-PAGE分析其相对分子量集中在14.3 ku和27.0 ku,18.0~21.0 ku,30.0 ku和37.0 ku,30.0 ku、37.0 ku以及44.3~59.0 ku区间;必需氨基酸含量基本符合FAO/WHO成人推荐标准;差示扫描量热(DSC)图谱分析表明JMG干粉出现两个吸热峰,变性温度分别为98.08℃和155.33℃,对应焓值为13.06 J/g、764.80 J/g;傅立叶红外光谱(FT-IR)分析其二级结构,显示JMG以α-螺旋为主;除起泡性和持水性明显低于大豆分离蛋白(SPI)外,JMG其它功能性质均与SPI基本相当。     

蚕豆蛋白的提取分离及相对分子质量的测定

分析了蚕豆清蛋白和球蛋白的组成及其亚基的相对分子质量.测得蚕豆清蛋白经过SepharoseCL 6B柱层析可洗脱出2个组分,球蛋白可洗脱出3个组分.SDS PAGE分析表明,蚕豆球蛋白7种亚基的相对分子质量分别为:54000,41400,38000,33600,18300,17500,16700.蚕豆清蛋白5种亚基的相对分子质量分别为:59000,55700,42000,38000,18600.     

鹅血中转铁蛋白质的分离纯化及其性质

以鹅血为原料,利用醋酸纤维膜电泳,分析鹅血中各球蛋白的质量浓度.采用DEAE 52离子交换和SephdexG 100凝胶层析等方法,对转铁蛋白(Transferrin,Tf)进行了分离纯化及其性质的研究.结果表明,鹅血浆中含有较多的β球蛋白,质量浓度为34.89mg/dL,每毫升血浆可纯化得到3.1mg转铁蛋白.鹅血含铁转铁蛋白(holo Tf)的特征吸收峰为470nm,相对分子质量为77000.鹅转铁蛋白对选用的革兰氏阴性菌 大肠杆菌有抑制作用,Fe3+能够改变转铁蛋白的结构,并影响转铁蛋白的抑菌功能.     

微生物转谷氨酰胺酶催化大豆11S球蛋白聚合研究

研究了微生物转谷氨酰胺酶（MtGase）催化大豆11S球蛋白的聚合反应条件。研究显示，TGase对11S的不同亚基反应不一样，它只能催化11S酸性亚基聚合，而碱性亚基几乎不受影响。离子强度I＝0．1时TGase催化活性要高于I＝0．5，这可能是酶海性受离子强度的影响。酶浓度范围为10－40U/g对TGase催化11S酸性亚基影响不大。TGase催化11S聚合的最适pH为7．0－8．0，pH过高或过低都不利于该酶反应。而在低于50℃范围内，温度越高TGase催化11S聚合越快达到平衡，37℃反应4h与50℃反应2h聚合效果差不多，而60℃已使TGase几利完全失活。     

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.     

脱脂米糠中清蛋白和球蛋白的提取工艺及氨基酸组成分析

脱脂米糠是重要的优质全价植物蛋白质营养源,其蛋白质中清蛋白含量最高,球蛋白其次。对米糠中清蛋白和球蛋白提取工艺进行了研究,探讨不同工艺因素对蛋白得率的影响,确定最佳提取工艺,并对产品的氨基酸组成进行测定。研究表明,清蛋白最佳提取工艺为料液比1∶14,提取时间3h,温度45℃,清蛋白得率可达14.64%;球蛋白最佳提取工艺为NaCl浓度为3%,料液比1∶10,提取时间2h,温度50℃,球蛋白得率为4.28%;两种蛋白质中必需氨基酸含量接近FAO/WHO推荐模式,是优质植物蛋白质来源。      

大豆7S球蛋白凝胶光学性质的研究

本文深入地研究了大豆7S球蛋白凝胶光学和流变学性质与蛋白质浓度、加热温度和加热时间的关系。结果表明在形成蛋白质凝胶(蛋白质浓度≥7.5%)的前提下,低的蛋白质浓度有利于大豆7S球蛋白形成透明性凝胶,但凝胶强度较低;温度＞85℃有利于蛋白凝胶透明性和强度的提高;加热60min.较为适宜。扫描电子显微镜(SEM)观察显示大豆7S球蛋白透明凝胶具有有序微观结构;探讨了大豆7S球蛋白形成透明凝胶机理。可为进一步研究大豆蛋白凝胶的光学性质和研制透明的大豆蛋白产品提供理论依据。     

Influence of high pressure on interactions of 11S globulin Vicia faba with ι-carrageenan in bulk solution and at interfaces

The influence of ι-carrageenan (ι-CAR) on the solution, interfacial and emulsifying properties of 11S globulin Vicia faba at low ionic strength and pH 8 has been investigated before and after high-pressure processing at 200 MPa for 20 min. The total calorimetric enthalpy (ΔH) and size exclusion chromatography studies for the pure 11S indicate that there is subunit dissociation and extensive aggregation of the protein during or following treatment. Under the same treatment conditions, 1-anilinonaphthalene-8-sulphonate (ANS) data has shown increased protein surface hydrophobicity. Pressure treatment of 11S gives much lower values of the surface tension, and apparent surface shear rheology experiments show that the molecules in the film adsorbed from the pressurised 11S are much more strongly interacting than those adsorbed from the native 11S. However, emulsions prepared with pressure processed 11S give substantially bigger droplets than those made with the untreated pure protein. Addition of ι-CAR to 11S reduces the denaturation temperature (T_m), the ΔH value, and protein surface hydrophobicity. Size exclusion chromatography at low ionic strength is indicative of complex formation. Tension measurements at the air–water interface are also consistent with the presence of a complex. Emulsions made with the simple 1:0.33 mixture of 11S+ι-CAR give emulsions with smaller droplets and pressure processing of the biopolymer mixture leads to emulsions with even smaller droplets. The presence of ι-CAR at low ionic strength appears to protect the globulin against pressure-induced aggregation.