Emulsification Properties of Succinylated Canola Protein Isolate

Emulsification properties of unmodified and succinylated canola (rapeseed) protein isolate (54 and 84% modification of free amino groups) were examined over a wide range of pH values (pH 3.5–11.0) and sodium chloride concentrations (0.0–0.70M). Both emulsification activity and emulsion stability were increased by succinylation, but extensive succinylation was not required to significantly improve these properties. Multiple regression analyses indicated that emulsification activity was related to protein solubility, hydrophobicity, zeta potential and flow behavior of aqueous dispersions of the proteins. Emulsion stability was affected by protein solubility, zeta potential, apparent viscosity of protein dispersions and difference in density between the aqueous and oil phase.     

Rheology and Microstructure of Succinylated Canola Protein Isolate

Steady shear rheological properties of aqueous dispersions of unmodified and succinylated canola (rapeseed) protein (54 and 84% modification of free amino groups) were examined over a wide range of pH (3.5–11.0) and NaCl concentration (0.0–0.70M). All dispersions were pseudoplastic and followed power-law or power-law plastic flow behavior. Apparent viscosity at shear rates of 10 and 1000 s-1 was affected by extent of succinylation, pH, NaCl concentration, and interactions among these factors. At both shear rates, protein solubility and hydrophobicity were reliable predictors of apparent viscosity. Dispersion microstructure, as revealed by light microscopy, appeared to play an important role in flow behavior.     

Soy Protein Isolate Solubility and Surface Hydrophobicity as affected by Antioxidants

Addition of tert-butylhydroquinone or a mixture of butylated hydroxyanisole and tert-butylhydroquinone (200 ppm on a lipid basis) during SPI processing gave increased protein solibility over that of the control (55%. 56% and 34%. respectively). These increased solubilities correspond to 32% and 18% decrease in oxidation of free sulfhydryls and 20% and 12% reduction in protein oxidation, as determined by protein carbonyl content. Increased protein solubilities, due to added antioxidants, were accompanied by higher total protein surface hydrophobicity, as determined by the sodium dodecyl sulfate (SDS) binding method, and soluble protein hydrophobicity, as determined by the fluorescence probe 8-anilino-1-naphthalene sulfonate (ANS).     

Relationships of Hydrophobicity and Net Charge to the Solubility of Milk and Soy Proteins

Protein hydrophobicity of 42 native and partially denatured milk and soy protein samples was determined fluorometrically by using three probes, 1-anilino-8-naphthalenesulfonate (ANS), cis-parinarate (CPA) and 1,6-diphenyl hexatriene (DPH), and chromatographically by using Phenyl Sepharose CL-4B (PSC). PSC and ANS hydro- phobicities correlated well to the protein insolubility determined at zero zeta potential, whereas no significant correlation was observed between CPA. hydrophobicity and protein insolubility. When backwards stepwise regression analysis was applied to 189 data of protein insolubility, a significant correlation (P < 0.001) was obtained between PSC hydrophobicity, zeta potential and protein insolubility. It is suggested that the aromatic hydrophobicity, in conjunction with zeta potential, may play a more important role in protein solublity than the aliphatic hydrophobicity.     

胡麻籽分离蛋白的溶解性与起泡性研究

为促进胡麻籽分离蛋白在食品工业中的应用,研究了pH值、盐浓度、蛋白质浓度等因素对其水溶性、起泡性和泡沫稳定性的影响。pH值对胡麻籽分离蛋白溶解度的影响呈典型的V形曲线。NaCl浓度为0.4mol/L前后胡麻籽分离蛋白表现出明显的盐溶与盐析效应。在0.1%～0.8%范围内,提高蛋白质浓度能增强起泡性与泡沫稳定性。在等电点附近,胡麻籽分离蛋白的起泡性最差但却具有最强的泡沫稳定性。NaCl对胡麻籽分离蛋白的起泡性的影响与其对溶解性的影响有相同的趋势。蔗糖能提高胡麻籽分离蛋白的泡沫稳定性,但当浓度高于5%时,对起泡性有负面影响。     

Solubility and Foaming Properties of Phytate-Reduced Soy Protein Isolate

A pilot scale ion exchange process was developed to produce a 75 - 77% phytate-reduced soy protein isolate. The solubility and foaming properties of this isolate were compared to those of control and commercial soy protein isolates as a function of protein concentration (5 and 10%, w/v), pH (3, 6 and 9) and preheat temperature (25, 60 and 80°C). Phytate-reduced soy protein extract exhibited minimum solubility at pH 4.8 - 5.0, compared to 4.2 - 4.5 for control soy extract. Phytate-reduced soy protein isolate was most soluble and functional at pH values below its isoelectric point (pH 3), whereas control and commercial soy isolates were generally most soluble and functional at pH values above their isoelectric point (pH 6 and 9).     

大豆分离蛋白结构特性与表面疏水性的关系

对不同品种大豆分离蛋白溶解性、表面疏水性、巯基含量进行测定,同时采用拉曼光谱法对蛋白质二级结构及氨基酸侧链进行分析,探讨大豆分离蛋白结构特性与表面疏水性关系。结果表明:不同品种大豆分离蛋白表面疏水性由大到小顺序依次为:东农46(743.87)皖豆24(730.14)黑农46(717.54)五星4(625.22)中黄13(613.38)冀NF58(600.61),并与溶解性呈负相关,与巯基含量呈正相关。不同品种大豆分离蛋白具有不同的二级结构,当α-螺旋含量降低、无规卷曲含量升高时,蛋白分子结构变的松散,使包埋在分子内部的疏水性残基更多的暴露出来,导致表面疏水性增加。     

pH 值对大豆分离蛋白构象及表面疏水性的影响

采用Lowery法、ANS荧光探针法、圆二色光谱、荧光光谱方法分别对不同pH值大豆分离蛋白溶解度、表面疏水性、蛋白质二级、三级结构进行分析。结果表明：随着pH值的升高,大豆分离蛋白的二级结构发生由β-折叠结构向α-螺旋结构的转变,其Trp残基所处微环境极性增强。大豆分离蛋白表面疏水性与溶解度呈负相关关系,同时大豆分离蛋白表面疏水性也与α-螺旋结构含量呈负相关关系。     

双低油菜籽分离蛋白提取方法对其功能性的影响

油菜籽蛋白是一种氨基酸组成合理的完全蛋白,其营养价值与酪蛋白不相上下,属于一类潜在的可食用优质蛋白。本文选冷榨油菜籽粕为原料,采用碱溶酸沉和电场絮凝的方法提取其中的油菜籽分离蛋白,并比较其结构和功能性。结果显示:电场方法提取的油菜籽蛋白ERP的表面疏水性为5.776±0.222,大于碱溶酸沉法的样品CRP(4.803±0.060),其乳化性(49.95%)、乳化稳定性(90.85%)及持油性(166.18%)均更优。ERP和CRP分子的二硫键含量分别为47.51 μmol/g和36.67 μmol/g。在电流的作用下,电场提取样品的α-螺旋及β-转角所占比例较高。结论:提取方法会影响油菜籽分离蛋白的氨基酸比例、结构及功能性。     

Spray-Dried Soy Protein Isolate Solubility, Gelling Characteristics, and Extractable Protein as Affected by Antioxidants

With the addition of antioxidants, spray-dried soy protein isolates (SPI) exhibited increased solubilities by 8% over the control in 0.1M NaCl. Increased solubilities corresponded to a 15% and 8% reduction in protein oxidation as determined by protein carbonyl contents. The greatest differences in solubility between a spray-dried SPI with antioxidant (66% protein solubility) and the control (54% protein solubility), as well as the minimum protein solubility, occurred in 0.2M NaCl. Following the initial solubilization step in SPI processing, amount of extracted proteins was increased by 4.5% over the control with addition of antioxidants. Gel fracturability, hardness and adhesiveness for heat set gels of 12% SPI processed with added antioxidants were increased by 26.3%, 23.5% and 24.6%, respectively.     

大豆分离蛋白溶解性能与水解度相关的研究

为了提高大豆分离蛋白的溶解性,利用Alcalase碱性蛋白酶,通过正交试验对大豆分离蛋白进行限制性水解,研究水解度对大豆分离蛋白溶解性的影响.结果表明:大豆水解蛋白在低水解度范围内(1.26%～7.93%),溶解性随水解度的增加呈指数增加.在最佳工艺条件下,温度60℃,pH 8.0,底物浓度9%,酶添加量4500 U/g,水解时间3 h,水解度可达为7.93%,溶解度达92.17%.并且大豆水解蛋白的溶解性受pH和离子强度等因素的影响,且影响程度随水解度的增加而减小.     

羟基自由基氧化对乳清蛋白疏水性的影响

本实验研究在羟基自由基氧化体系中,不同的H2O2 浓度(1～20mmol/L)、FeCl3 浓度(0.1～2mmol/L)以及不同的pH 值、温度、盐浓度等环境条件对乳清蛋白疏水性的影响,每种氧化条件的氧化时间分别为1、3、5h。结果表明,氧化和环境因素对乳清蛋白的疏水性影响很大,在H2O2 体系中当H2O2 浓度为5mmol/L 时疏水值达到最大,为9559.2,是对照组的4.88 倍,明显高于FeCl3 体系中的变化;疏水性在偏离等电点pH7.0 时较大,在适宜的温度和盐浓度下能够增加乳清蛋白的疏水性。说明氧化过程中,乳清蛋白的疏水性受H2O2 浓度的改变影响最大,并且也受其他环境条件的影响。     

高场强超声波对大豆分离蛋白溶解性的改善作用

本研究探讨了高场强超声处理对3%(W/V)和5%(W/V)两种质量体积分数的商业大豆分离蛋白(SPI)溶解性的影响,进而分析其对SPI表面疏水性、粒径和电泳的影响,解析结构变化对溶解性的影响机制。结果表明,200～800 W高场强超声波处理均可显著(p0.05)提升两种质量浓度商业大豆分离蛋白的溶解性,随超声功率的增大,SPI溶解性呈现先增加后降低的趋势,其中400W的超声处理3%(W/V)SPI可获得最大的溶解度(47.86%),比对照样品提高了87.4%。除800 W超声处理外,超声处理后3%(W/V)SPI的溶解性均大于5%(W/V)SPI的溶解性。表面疏水性、粒径结果表明,低功率超声处理可使SPI聚集体部分解聚,蛋白表面疏水性下降,粒径降低,溶解性增加;而高功率超声处理可使SPI重新形成不溶性聚集体,致使溶解性下降。电泳结果表明,超声处理没有破坏蛋白亚基结构。结果表明3%(W/V)SPI经400W的超声处理可获得最优的溶解性改善效果。本研究可为商业大豆分离蛋白溶解性提高提供方法指导。     

中性蛋白酶酶解酰化大豆分离蛋白功能特性的研究

利用中性蛋白酶对琥珀酰化大豆分离蛋白进行酶解改性,考察pH值、酶解温度和加酶量对其功能特性的影响,通过单因素和中心组合试验确定最优酶解改性条件:pH值为6.82、酶解温度为48℃、加酶量为6627U/mL。酶解改性后琥珀酰化大豆分离蛋白的功能特性均有较大提高,与改性前的大豆分离蛋白相比溶解度、乳化性、乳化稳定性、起泡性和起泡稳定性分别提高了32.28、3.89、4.41、2.5、1.22倍。     

大豆分离蛋白热性质及其空间构象对表面疏水性的影响

采用差示量热扫描(DSC)法和荧光光谱法对不同品种大豆分离蛋白的热性质和空间构象进行分析,探讨大豆蛋白的热性质和空间构象对其表面疏水性的影响。结果表明,不同品种的大豆分离蛋白的7S球蛋白与11S球蛋白的Td值、△H值与表面疏水性存在显著负相关,即7S球蛋白与11S球蛋白的Td值、△H值越小,表面疏水性越大。原因是△H值越低,分子相对伸展使疏水性残基暴露较多,导致蛋白质具有相对较大的表面疏水性。荧光光谱表明6种大豆分离蛋白具有典型的色氨酸发射光谱,荧光峰峰位之间存在显著性差异,并且不同品种的大豆分离蛋白随着荧光峰峰位数值和峰强越大,色氨酸残基的微环境极性越强,表面疏水性越高。这与大豆品种密切相关,埋藏在内部的疏水基团的暴露是导致表面疏水性增大的主要原因。     

脱酚及pH偏移处理对菜籽蛋白体外模拟消化的影响

研究了脱酚及pH偏移处理对菜籽蛋白(CPI)及乳液模拟体外消化的影响。采用蛋白凝胶电泳、显微镜观察、粒度分析等方法进行表征。结果表明,在体外消化的过程中,蛋白水解度(DH)整体呈上升趋势,经脱酚、pH偏移及二者协同处理后的DH分别增大了17.1%、2.6%和22.9%。仅脱酚处理使消化产物可溶性蛋白浓度提高了22.3%。SDS-PAGE的结果显示,cruciferin(12S)比napin(2S)更易于水解,并且脱酚导致蛋白在12 kDa以下的条带消失。pH偏移处理显著提高了CPI的自由基清除能力,并改善了由酚的脱除引起的自由基清除能力的降低。对于改性后的蛋白乳液,脱酚导致胃消化阶段更显著的乳液液滴聚集现象,同时降低了肠消化阶段的油滴大小。总的来说,脱酚处理提高了蛋白及乳液的消化率,pH偏移提高了蛋白的自由基清除能力。     

Xanthan Gum Effects on Solubility and Emulsification Properties of Soy Protein Isolate

The effect of xanthan gum (XG) on solubility and emulsifying properties of soy protein isolate (SPI) was evaluated. The solubility of SPI was increased by addition of XG (p < 0.05). The emulsifying activity of SPI-XG was 4 times higher than that of SPI or XG alone (p < 0.05) and similar to that of bovine serum albumin (BSA) (P > 0.05). The emulsifying stability of SPI-XG dispersions was respectively 3 and 2 times higher than that of SPI and BSA (p < 0.05). The solubility and emulsifying properties of SPI-XG dispersions were stable over a wide range of pH (3.0 to 9.0), ionic strength (0.1 to 1.0M NaCl), and heat (85°C, 1 hr).     

双酶复合改性增强大豆分离蛋白溶解性研究

传统方法对大豆分离蛋白(SPI)进行改性,一般只可改善一个或几个功能性,而SPI溶解性和分子量不能兼得。利用中性蛋白酶和谷氨酰胺转胺酶(TG)对大豆分离蛋白进行复合改性,通过单因素和正交实验研究,中性蛋白酶酶解最佳工艺条件:温度60℃,时间0.5小时,pH7.0,酶用量4000u/g,SPI溶解性可达97.9%;再经TG改性,所得聚合物虽有很大分子量,但还可改善SPI溶解性,并且乳化性、发泡性均有提高。     

低温冷冻条件对大豆分离蛋白分散液表面疏水性及二硫键的影响

通过大豆分离蛋白（soybean protein isolate,SPI）冷冻前后结构的变化,研究了低温冷冻条件（SPI添加量、冷冻温度、冷冻时间）对SPI结构（巯基、二硫键及表面疏水性）的影响。实验发现在冷冻条件下随着SPI添加量的降低,游离巯基和二硫键逐渐减少、暴露巯基与表面疏水性先增加后减小;随着冷冻温度降低和冷冻时间延长,SPI的游离巯基、二硫键含量及表面疏水性逐渐减少。经过冷冻处理的SPI会有一定程度的变性,在不太低的冷冻温度下游离巯基含量明显大于未冷冻SPI,且在冷冻过程中SPI大部分的分子内二硫键转化为分子间二硫键。     

Influence of Denaturation, Hydrophobicity and Sulfhydryl Content on Solubility and Water Absorbing Capacity of Soy Protein Isolates

Solubility and water absorbing capacity of commercial soy protein isolates were correlated with structural parameters. The physico-chemical properties studied were degree of protein denaturation, surface hydrophobicity and sulfhydryl groups. The results indicated that solubility and water absorption were affected differently as the parameters were varied. These functional properties depended on more than one structural parameter. Solubility in 0.2M NaCl solution provided information about the degree of denaturation of soybean protein isolates. Isolates with highly denatured proteins, high surface hydrophobicity, low solubility in 0.2M NaCl solution and low SH exhibited the highest water absorbing capacity.