XG-g-NVP共聚物对果汁中多酚物质吸附/解吸行为研究

Polyphenols of fruit juice are both the functional material with a variety of physiological activity and the main components that caused browning and post turbidity of fruit juice. Xanthan gum grafted N-vinyl pyrrole (XG-g-NVP) is a kind of copolymer with good adsorption activity for polyphenols. To ensure the quality of fruit juice and make full use of fruit juice polyphenols, it is necessary to carry out research on adsorption/desorption behaviors of XG-g-NVP copolymer for polyphenols in fruit juice. Through analyzing the relationship between independent variable, sunch as graft ratio, temperature, pH value, polyphenol concentration, flow rate of fruit juice, and the dependent variable of polyphenols adsorption, we discuss the dominant factors that affect adsorption/desorption behaviors of XG-g-NVP for polyphenols in static and dynamic conditions; we apply separately some classic kinetic equation,such as Elovich equation, and thermodynamic equation,such as Langmuir, Freundlich and Linear equations to fitting the experimental result in research on the dynamics and thermodynamics of adsorption/desorption of XG-g-NVP copolymer for polyphenols and analyse and calculate the △H、△G和△S in adsorption/desorption process;Through a variety of instrument analysis method,such as EPR, XRD and SEM, we analyse the characteristic and nature of the surface of XG-g-NVP before and after adsorption of polyphenols and reveals the characteristics and mechanism of adsorption/desorption behavior of XG-g-NVP copolymer for polyphenols in order to provide theoretic support in removing polyphenols of juice and recycle them by applying XG-g-NVP copolymer.

果汁中的多酚既是具有多种生理活性的功能性物质，又是造成果汁褐变和后混浊的主要成分。黄原胶接枝吡咯烷酮（XG-g-NVP）是一种对多酚具有良好吸附的共聚物。为保障果汁质量安全和充分利用果汁中的多酚，有必要开展XG-g-NVP共聚物对果汁中多酚物质吸附/解吸行为的研究。本项目以接枝率、温度、pH值、多酚浓度、果汁流速等为自变量，多酚吸附量为因变量，探讨静态和动态条件下影响XG-g-NVP吸附/解吸多酚的主导因素；开展多酚吸附/解吸的动力学研究，采用Elovich等方程进行拟合；开展多酚吸附/解吸的热力学研究，采用Langmuir、Freundlich和Linear等方程进行拟合，分析计算吸附/解吸的△H、△G和△S，并采用EPR等多种仪器对XG-g-NVP吸附/解吸多酚前后的表征进行分析，揭示多酚吸附/解吸行为的特性和机理，以便于XG-g-NVP在果汁中多酚的去除和回收应用方面提供理论支撑。

本项目首先采用辐照法制备了不同接枝率的XG-g-NVP接枝共聚物，并采用红外、XRD及电镜扫描等方法对XG-g-NVP接枝共聚物进行表征；然后用上述XG-g-NVP接枝共聚物进行不同接枝率，温度、pH值、吸附时间等条件下对果汁中多酚静态吸附量/解吸量、吸附率/解吸率影响的测试；根据接枝率对静态吸附量/解吸量、吸附率/解吸率的影响，筛选出最佳接枝率；最后进行了静态吸附热力学特性测定以及静态吸附动力学特性测定。研究结果表明，XG-g-NVP的溶胀性能随接枝率的增大呈先增加后减小的趋势，25℃时接枝率为557%的共聚物最大溶胀度为80.01g/g。XG-g-NVP对茶多酚的吸附力是多酚的羟基与NVP的内酰胺结构中的羰基所形成的氢键，吸附发生在共聚物的结晶区，吸附使共聚物的结晶度下降。当接枝率为516%和557%时，茶多酚和原花青素的吸附量分别达到最大值1.059 g•g-1和1.515 g•g-1，吸附在60 min内可达到平衡，酸性条件有利于共聚物对多酚的吸附。吸附可自发进行，吸附行为符合Lagergren二级动力学方程和Freundlich 吸附等温式。当解吸时间和乙醇浓度分别为40 min和65%时，共聚物对茶多酚和原花青素具有较好的解吸效果。研究表明XG-g-NVP共聚物可作为茶多酚和原花青素的高效吸附材料。同时，研究表明，添加少量的接枝共聚物即可对葡萄果汁起到澄清的作用，并且不会明显影响果汁的芳香气味与口感。因此，XG-g-NVP接枝共聚物作为多酚类物质的高效吸附剂和果汁的澄清剂方面具有较好的应用前景。