【作者】 赵冠里；

【导师】 赵谋明；

【作者基本信息】 华南理工大学 ， 食品科学， 2011， 博士

【摘要】 花生蛋白是我国重要的植物蛋白资源,但目前并未被有效利用。本论文旨在探寻适于花生蛋白资源利用的途径。研究了花生球蛋白与伴球蛋白组分的物化和功能特性,探讨了花生分离蛋白在制备过程中的变性程度,酶解或多糖接枝改性技术对花生分离蛋白功能特性的影响,并进一步研究了其相关改性机理。主要研究结果如下:对花生球蛋白（arachin）与伴球蛋白（conarachin）的物化和功能特性进行了分析和比较,从蛋白结构与功能性关系角度揭示了两者功能性差异的机制。结果表明,花生球蛋白在等电点附近（pH4.5-6.0）比花生伴球蛋白具有更高的溶解性（PS）,而在偏离等电点时其溶解性低于伴球蛋白,花生伴球蛋白的乳化活性指数（EAI）、起泡能力（FC）和凝胶能力显著高于花生球蛋白（P<0.05）;花生球蛋白的变性温度Td（104.84℃）及焓变值ΔH(13.78 Jg^-1)显著高于花生伴球蛋白的变性温度（89.47℃）与焓变值(8.11 Jg^-1)（P<0.05）;花生球蛋白分子表面的巯基（SH）较少,大部分巯基包裹于球蛋白分子内部,而花生伴球蛋白中大部分巯基暴露于分子的表面。圆二色谱（CD）、荧光光谱和表面疏水性（H₀）分析表明,花生伴球蛋白比花生球蛋白具有更疏松的三级结构和更高的界面活性。花生蛋白经碱溶酸沉提取后其溶解性（PS）、乳化活性指数（EAI）、起泡能力（FC）和凝胶能力均有不同程度的下降。碱溶酸沉提取使花生球蛋白中分子量为97.4 kDa的亚基条带消失,而伴球蛋白亚基条带无明显变化;相对于天然花生蛋白（NPP）,花生分离蛋白（PPI）中球蛋白与伴球蛋白组分的变性温度（Td）与变性焓（ΔH）显著降低（P<0.05）;碱溶酸沉提取过程使花生蛋白中暴露巯基、总巯基和二硫键含量降低。圆二色光谱（CD）、荧光光谱和表面疏水性（H₀）分析表明,花生分离蛋白发生部分变性,其制备过程中的酸碱处理导致蛋白分子伸展、H₀增加及三级结构的改变。蛋白变性是导致分离蛋白功能特性降低的主要原因。花生球蛋白的酸性亚基（42 kDa和39kDa）对Alcalse酶解相对更加敏感,其次为花生伴球蛋白亚基（66 kDa）和花生球蛋白的碱性亚基（22 kDa）。酶水解降低了花生球蛋白与伴球蛋白组分的焓变值（ΔH）,增加了球蛋白组分的热稳定性并且导致花生分离蛋白酶解产物中二硫键含量迅速升高。荧光光谱分析可知Alcalse蛋白酶酶解使花生分离蛋白的空间构象更加疏松,易于水分子的直接进入和水化,因而显著改善了花生分离蛋白的溶解性、起泡能力和热诱导凝胶形成的能力,但破坏了花生分离蛋白形成乳状液的能力。在干热条件下,花生分离蛋白中的伴球蛋白组分易与葡聚糖发生交联反应生成大分子的接枝产物,而花生球蛋白较难与葡聚糖发生反应,这限制了花生分离蛋白与葡聚糖整体的糖接枝反应程度;与葡聚糖的混合或者接枝反应显著地改善了花生分离蛋白的热稳定性（P<0.05）,但使其空间构象变得更加紧凑,导致蛋白质内部包裹的赖氨酸残基很难与多糖发生接枝反应;与葡聚糖的接枝反应使花生分离蛋白的溶解性显著提高,尤其改善了其在酸性条件（pH 4.5–6.0）下的溶解性（P<0.05）;与葡聚糖的混合过程会显著改善花生分离蛋白的乳化和起泡特性（P<0.05）,而糖接枝反应能够在此基础上进一步改善其相关的功能特性,当干热反应至第7d,其乳化活性指数与起泡能力达到最优值,分别为120 m²/g和87%。花生球蛋白与葡聚糖能够在干热条件下进行美拉德反应生成多糖接枝产物。花生球蛋白酸性亚基比碱性亚基更易与葡聚糖发生接枝反应。对花生球蛋白的预加热处理不能提高其与葡聚糖的反应速度。花生球蛋白与热处理花生球蛋白在与多糖接枝反应过程中,其三级结构皆变得更加紧凑,限制了蛋白与多糖的接枝反应速度与反应程度。未经热预处理的花生球蛋白与多糖的接枝产物具有很高的溶解性和乳化活性,在干热反应第14d其溶解性和乳化活性指数达到实验条件下的最高值,分别为95%和149 m²/g。更多还原

【Abstract】 Peanut protein is one of the most important and underutilized protein resources in China. The aim of this study was to explore utilization means for proteins from peanut protrein. Physiochemical and functional properties of arachin and conarachin fractions was studied and compared, the related mechanism was elucidated. Enzymatic hydrolysis and conjugation with dextran were used to modify peanut protein isolate for improving its functional properties. The possible relationship between structure and functional properties of peanut protein isolate was also discussed. Main results are as follows:Arachin had higher thermal stability, more ordered structure and lower cooperativity of the thermal transition than conarachin. Most of free SH of arachin was buried in the interior while most of them of conarachin was located at the surface. TheΔH of arachin was remarkable higher than conarachin. The surface hydrophobicity of conarachin was higher than arachin. Compared with conarachin, arachin had the more compacted tertiary conformation. Conarachin had the higher solubility than arachin except at near pI. Conarachin had better emulision ability index, foam capacity and gel properties than arachin.Peanut protein isolate (PPI) was extracted by alkali dissolution and acid precipitation from defatted peanut flour. The effects of extraction conditions on the denaturation and functional properties of PPI were investigated. In comparison with native peanut protein (NPP) which was extracted by ammonium sulfate, the PPI extracted by alkali dissolution and acid precipitation had a higher extent of denaturation. Arachin was affected more easily by the extraction process than conarachin and led to a noticeable decrease of thermal stability of PPI. PPI contained much lower sulfhydryl and disulfide bond contents than NPP. The analyses of intrinsic fluorescence spectra indicated a more compacted tertiary conformation of NPP than PPI. Extraction process influenced the functional properties of PPI, such as protein solubility, emulsifying activity index and foaming capacity. The relatively poor functional properties of PPI might be associated with protein denaturation/unfolding and subsequent protein aggregation.Effects of limited enzymatic hydrolysis by Alcalase on the conformational and functional properties of peanut (Arachis hypogaea L.) protein isolate (PPI) were investigated. Acid subunits of arachin were most susceptible to Alcalase hydrolysis, followed by conarachin and the basic subunits of arachin. Enzymatic hydrolysis increased the thermal stability of arachin and led to a sharp increase of the number of disulphide bonds with a decrease of sulfhydryl group in PPI hydrolysates in comparison with PPI. The analysis of intrinsic fluorescence spectra indicated more loosed tertiary conformation of PPI hydrolysates than PPI. The limited emzymatic hydrolysis improved the functional properties of PPI, such as protein solubility and gel-forming ability, but impaired the emulsifying activity index.Reaction mixtures containing peanut protein isolate (PPI) and dextran (1:1 weight ratio) were dry-heated at 60℃and 79% relative humidity for 7 days. SDS-PAGE analysis indicated PPI had become complexed with dextran to form conjugates of higher molecular weight. Arachin, accounting for over 50% of peanut proteins, was hard to glycosylate with dextran, which might limit the extent of glycosylation of PPI. The thermal stability of PPI has been remarkably improved by mixture/conjugation with dextran. Proteins in mixtures/conjugates might have a more compacted tertiary conformation than PPI. The protein solubility of conjugates at pH 4.5–6.0 was remarkably increased compared with the PPI/mixture. Mixture with dextran could significantly improve the emulsifying and foaming properties of PPI (p < 0.05). Conjugation with dextran could further enhance emulsifying and foaming properties of PPI on the base of mixture.Arachin can become complexed with dextran to form conjugates of higher molecular weight. Acid subunits of arachin were earier to glycosylate with dextran than basic subunits. The heat-pretreatment of arachin could not increase the speed of Maillard reaction with dextran. Proteins in mixtures/conjugates might have a more compacted tertiary conformation than arachin, which might limit the extent of glycosylation. The conjugation with dextran could improve the solubility and emulsifying properties of arachin, while it was hard to improve the functional properties of arachin. pretreated by heat.更多还原