沙蒿多糖乳化性的构效关系研究

Polysaccharides based emulsifiers are more and widely accepted by consumers due to the safety, nutritional and multi-functional properties of the polysaccharides, while the overall supply is short. ASK polysaccharide has large abundance and are widely distributed in China. This polysaccharide also demonstrated good emulsifying properties in our pre-experiments. However, limited information is available regarding the structure and emulsification properties of ASK polysaccharides. We made a hypothesis that the degree of branching, linkage pattern of protein residue and the presence of hydrophobic groups are main contributes to the good emulsifying properties. The main objectives of this project are (1) modifying ASK polysaccharide molecules using ultrasonication, NaOH and enzyme degradation, deprotein and heating process in order to clarify the hydrophobic group, molecular weight, degree of branching, and linkage pattern of protein, and in further uncover the fine structure of this polysaccharides; (2) Clarifying the emulsifying properties of ASK polysaccharides by testing the rheological properties, surface activity, emulsifying activity and stability of this polysaccharide; (3) Understanding the conformational properties of this polysaccharide using HPSEC coupled with triple detector as well as static & dynamic light scattering techniques; (4) Establishing the relationships of structure conformation and emulsifying properties relationships of ASK polysaccharide in the perspective of molecular level, aiming to provide theoretical foundation and experimental data for this natural occurring polysaccharide.

多糖类乳化剂是深受消费者信赖的天然、营养、多功能的安全添加剂，但供应量有限。沙蒿多糖含量高、分布广，且预实验发现，沙蒿多糖具有乳化特性。目前对沙蒿多糖结构和乳化作用还不清楚。我们推测支链度、蛋白质残基连接方式和连接位置及分布规律是影响沙蒿多糖乳化性的重要结构特征。针对这些科学问题，本项目拟通过（1）超声波降解、NaOH水解、酶水解、脱蛋白和加热处理构建沙蒿多糖分子修饰组分体系，阐明亲油基团、分子量、支链度、蛋白质残基连接方式和连接位置及整体分布规律，剖析沙蒿多糖分子精细结构；（2）测定沙蒿多糖分子修饰体系的流变学、表面活性、乳化活性和稳定性，阐明沙蒿多糖乳化机理；（3）利用凝胶排阻色谱结合光散射技术探讨沙蒿多糖的构象特征；（4）阐明沙蒿多糖乳化特性构效关系。从分子机理角度研究沙蒿多糖结构、构象以及乳化性和乳化稳定性之间构效关系，为天然多糖乳化剂提供理论和实验依据。

沙蒿多糖（ASKP）是一种溶于水可形成粘稠溶液，可有效降低油/水界面张力的多糖，具有开发为多糖乳化剂的潜力。本研究通过多糖酶水解、蛋白酶水解及乙酰化反应等方法，实现沙蒿多糖(ASKP)、高分子量沙蒿多糖（60P）和低分子量沙蒿多糖（60S）分子的结构修饰，从分子特性、流变学特性、乳化活性及乳化稳定性等方面系统地研究了结构修饰对沙蒿多糖乳化性的影响。研究结果表明：（1）多糖酶水解后，ASKP、60P及60S的分子量、分子尺寸均发生降低，ASKP中60P及60S的构象更加松散，呈无规卷曲；ASKP及60P溶液的表观粘度降低，油/水界面张力显著降低。酶解后，60S溶液仍保持极低粘度状态，油/水界面张力降低，但无显著差异。多糖酶水解后，ASKP及60P的乳化性增强，60S的乳化性减弱。（2）脱蛋白处理后，ASKP中60P的分子量及分子尺寸大幅降低，构象更加松散，呈无规卷曲。ASKP溶液的表观粘度降低，油/水界面张力升高，但无显著差异。脱蛋白处理后，ASKP的乳化性减弱。（3）乙酰化反应使ASKP中60P及60S分子均发生降解，分子量及分子尺寸降低。随着乙酰化度的增加，乙酰化ASKP的分子量及分子尺寸逐渐增大并超过ASKP，ASKP的构象变得更加紧密，趋向于球状。随着乙酰化度的增加，乙酰化ASKP溶液的表观粘度逐渐增大并超过ASKP。乙酰化反应使乙酰化ASKP溶液的油/水界面张力显著降低，ASKP的乳化性随乙酰化度的增加逐渐提高。（4）分子量及分子尺寸是ASKP乳化性的重要因素。较低的分子量及较小的分子尺寸利于ASKP及60P乳化性的提升，但会降低60S的乳化性。蛋白质的存在利于60P高分子量结构的维持，对ASKP的乳化性至关重要。乙酰化反应可提升ASKP的乳化性，且乙酰基对ASKP乳化性的影响高于分子量及分子尺寸的影响。分子构象对ASKP乳化性的影响较小。本研究初步探讨了ASKP的结构特性与其乳化性的构效关系，为ASKP乳化剂的开发和应用奠定了理论和实验基础。