【作者】 郭庆；

【导师】 木泰华；

【作者基本信息】 中国农业科学院 ， 食品科学， 2010， 硕士

【摘要】 甘薯加工中产生的大量废水含有多量的甘薯蛋白,经过回收利用可减少资源的浪费和环境的污染,甘薯蛋白又是具有显著保健功能和加工特性的优质植物蛋白,因此,研究其乳化特性及机理具有重要理论意义和实践价值。本研究采用碱溶酸沉的工艺从甘薯块根组织中提取甘薯蛋白,主要研究了不同物化因素(蛋白浓度,油相体积分数,pH,NaCl和CaCl2)对甘薯蛋白乳化特性(乳化活性和乳化稳定性)的影响,分别测定了不同物化条件下甘薯蛋白乳化液的乳化颗粒平均粒径(d4,3)、乳化活性指数(EAI),乳化稳定性指数(ESI)、乳析指数、界面性质(界面吸附蛋白浓度及组成)和流变性质,并初步探索了不同物化因素影响甘薯蛋白乳化特性的机理。增加蛋白浓度能显著地降低乳化液的平均粒径,EAI和表观粘度,却显著地增加ESI和界面蛋白浓度。相比之下,增加油相体积分数能显著地增加乳化液的平均粒径,EAI和表观粘度,但却使乳化液的ESI和界面吸附蛋白的浓度降低(P < 0.05)。SDS-PAGE观察知甘薯蛋白乳化液界面吸附蛋白主要由Sporamin A, Sporamin B和一些由双硫键连接形成的高分子物质组成。在高pH条件下(7,8)乳化液的稳定性较好且EAI较高,随着pH的降低乳化液的稳定性逐渐降低且EAI也逐渐降低,但当pH降到等电点以下,其EAI和ESI又有所升高。由于pH=2时,蛋白分子的表面疏水性较高而造成疏水相互作用的增大引起颗粒间引力增大,故同pH=3相比,pH=2时乳化液的EAI和ESI又都有所降低。低pH环境(2,3,4)显著地改变了甘薯蛋白的结构使乳化液界面吸附蛋白浓度增大,并造成Sporamin A二聚体的形成。加入0.2 M NaCl,甘薯蛋白乳化液的EAI和ESI显著地降低,且初始剪切黏度显著地增大,这主要是因为静电屏蔽作用引起蛋白分子间相互作用力增强。SDS-PAGE显示NaCl对甘薯蛋白乳化液界面吸附蛋白的组成影响较小。添加0.05 mol·L-1氯化钙后甘薯蛋白乳化活性指数由未添加氯化钙的30.3 m2·g-1显著地降低至27.6 m2·g-1,d4,3从4.2μm显著地增大至4.42μm(P<0.05)。然而,随着氯化钙浓度进一步的升高(0.10-0.25 mol·L-1),d4,3显著地增大(P<0.05)而甘薯蛋白乳化活性指数变化并不显著(P>0.05)。此外,添加较高浓度的氯化钙能显著地增加乳化液的乳析指数和初始表观粘度,且界面吸附蛋白的浓度也显著提高(P<0.05)。SDS-PAGE分析发现添加氯化钙后Sporamin A不易被甘薯蛋白乳化界面吸附,且乳化界面和乳化液中均存在>66kDa的S-S键高分子聚合物。研究发现蛋白浓度,油相体积分数,pH,NaCl和CaCl2均能显著地影响甘薯蛋白乳化液的乳化性质。更多还原

【Abstract】 The waste solution produced in sweet potato processing contains large amounts of sweet potato protein. Recycling sweet potato protein from waste solutions can reduce the waste of resources and the pollution to the environment. Furthermore, sweet potato protein has significant bioactive functionality and it is a high-quality plant protein with good processing characteristics. Therefore, there are important theoretical and practical value to study the emulsifying properties and its mechanism of sweet potato protein.Sweet potato protein (SPP) was prepared through isoelectric precipitation. The effect of physicochemical conditions (protein concentrations, oil volume fractions, pH, NaCl and CaCl2) on properties of stabilized emulsions of SPP were investigated by use of emulsifying activity index (EAI), emulsifying stability index (ESI), droplet size, rheological properties and interfacial properties in different physicochemical conditions, and initially explored the mechanism of the effect of different physicochemical factors on emulsifying properties of SPP.Increasing of protein concentration greatly decreased droplet size, EAI and apparent viscosity of SPP emulsions; however, there was a pronounced increase in ESI and interfacial protein concentration (P < 0.05). In contrast, increasing of oil volume fraction greatly increased droplet size, EAI and emulsion apparent viscosity of SPP emulsions, but decreased ESI and interfacial protein concentration significantly (P < 0.05). The main components of adsorbed SPP at the oil–water interface were Sporamin A, Sporamin B and some high-molecular-weight aggregates formed by disulfide linkage.At higher pH (7, 8), the EAI and ESI is high while with the decrease of pH (8-4) the EAI and ESI decreased. However, when pH is below pI, the EAI and ESI increased again. Compared with emulsion at pH 3, the EAI and ESI of SPP emulsions at pH 2 decreased due to the intense hydrophobic interaction. The structure of SPP changes significantly, which leads to the increase of interfacial protein concentration and the formation of dimmer of Sporamin A. Compared with SPP emulsions without NaCl, the EAI and ESI of SPP emulsions with addition of 0.2 M NaCl decreased significantly, and the initial apparent viscosity increased markedly as well, which can be attributed to reducing electrostatic repulsion between droplets through electrostatic screening. SDS-PAGE show that NaCl has little effect on the composition of interfacial adsorbed protein.The EAI of SPP emulsions decreased significantly from 30.3 m2·g-1 to 27.6 m2·g-1 after the addition of 0.05 mol·L-1 calcium chloride, while the d4,3 increased from 4.2μm to 4.42μm (P<0.05). Nevertheless, with the further increase in concentrations of calcium chloride (0.10-0.25 mol·L-1), the EAI had no obvious difference (P>0.05), but the d4,3 had a marked increase (P<0.05). In addition, the CI, interfacial adsorbed protein concentration and initial apparent viscosity were increased markedly by adding higher concentrations of calcium chloride (P<0.05). Furthermore, SDS-PAGE showed that with addition of calcium chloride Sporamin A was not easy to be adsorbed at oil/water interface, and that the high molecular polymers (>66kDa) formed by S-S bonding existed both in oil/water interface and continuous phase of emulsions. The study found that these physicochemical conditions can significantly affect the emulsifying properties of SPP.更多还原