通过膳食植物多酚可以起到保健和治疗多种疾病的目的。茶叶中主要的儿茶素表没食子儿茶素没食子酸酯(EGCG)具有多种功效，如抗氧化、抗炎症、抗肿瘤、降血脂等。然而，EGCG在中碱性环境中不稳定，易发生聚合和降解，其体内生物利用率较低，严重限制了其在各个领域的应用。众多研究表明采用纳米材料包封EGCG可以提高其在碱性环境下的稳定性，增强其在胃肠道的吸收。壳聚糖是一种天然可降解的高分子材料，具有良好的生物相容性，并且安全无毒，已经广泛应用于纳米材料的制备。 在以前的研究中，我们通过自组装的方法制备了包封EGCG的壳聚糖（CS）-酪蛋白磷酸肽（CPP）纳米复合物。体外释放动力学表明该纳米复合物具有良好的缓释作用，并且Caco-2细胞模型实验表明CS-CPP纳米复合物可明显增强EGCG的肠渗透性和吸收，从而增强了其生物利用率。然而包封EGCG的纳米复合物的生物学性能还没有被研究。本研究通过SAXS技术探究壳聚糖和CPP之间的相互作用，制备CS-EGCG-CPP纳米复合物，考察其在碱性环境下对EGCG稳定性的保护作用，并系统评价其在体外的抗氧化和抗炎症作用。主要研究结果如下： 1. CS-EGCG-CPP纳米复合物的制备、表征及其在碱性环境下的稳定性 小角X射线散射（SAXS）是一种有效的表征多肽和多糖之间相互作用的方法。胃肠道的pH值变化（2.0-6.2）可引起壳聚糖和CPP之间的的相互作用，形成CS-CPP复合物。CS-CPP复合物内部的Df值的大于3，表明形成了致密颗粒，并且Df值一般随CS/CPP质量比的提高而增大。研究CS浓度、CS/CPP质量比和EGCG浓度三个因素对制备的CS-EGCG-CPP纳米复合物的粒径和包封率的影响。纳米复合物的粒径随CS和EGCG浓度的增大而增大，随CS/CPP增大而减小。包封率随CS/CPP增大和EGCG浓度的增加而降低，但随着CS浓度的增加，呈现出先增大后降低的趋势。透射电镜显示制备的包封EGCG的CS-CPP纳米复合物呈规则的球形，分散均匀，平均粒径208 nm，纳米复合物表面的zeta电位为+25.6 mV。CS-EGCG-CPP纳米复合物能够显著（p< 0.01）增强EGCG在碱性环境下（pH 7.4）的稳定性。 2. CS-EGCG-CPP纳米复合物抗氧化活性的研究 化学抗氧化实验表明CS-EGCG-CPP纳米复合物具有与EGCG相似的总还原力、铁离子还原力（FRAP）、清除ABTS自由基和清除超氧阴离子自由基能力。并且显示出高于EGCG的金属离子螯合活性。在细胞水平，CS-EGCG-CPP纳米复合物表现出比EGCG更强的对H2O2诱导RAW264.7细胞氧化损伤的保护作用。 3. CS-EGCG-CPP纳米复合物抗炎症活性的研究 利用LPS诱导RAW264.7和Caco-2细胞建立体外炎症模型。在RAW264.7细胞模型中，CS-EGCG-CPP纳米复合物能显著抑制TNF-α、IL-6、IL-1β和NO的释放。在Caco-2细胞模型中，CS-EGCG-CPP纳米复合物能显著抑制TNF-α和IL-8的分泌。并且在两种模型中，CS-EGCG-CPP纳米复合物都表现出比含有相同EGCG浓度的游离EGCG更强的抑制炎症介质分泌的能力。通过蛋白免疫印迹测定发现CS-EGCG-CPP纳米复合物具有比游离EGCG更好的抑制LPS诱导的RAW264.7细胞中iNOS表达的能力。在两种细胞模型中，CS-EGCG-CPP纳米复合物和游离的EGCG都能调控NF-κB信号通路，抑制IκB的降解和磷酸化以及p65的表达。相比游离的EGCG，CS-EGCG-CPP纳米复合物的抗炎症活性得到显著提高。

Dietary polyphenols plays an important role in health care and treatment of various diseases. Epigallocatechin gallate (EGCG), the main catechin in tea, possesses many therapeutic effects such as antioxidant, anti-inflammatory, anti-tumor, hypolipidemic and so on. However, EGCG is prone to polymerization and degradation in moderately alkaline environments, resulting in instability and low bioavailability, which seriously limit the application of EGCG. Numerous studies have shown that encapsulation of EGCG with nanomaterials can enhance its stability under alkaline conditions and enhance its absorption in the gastrointestinal tract. As a food grade polymer material, chitosan has favorable biodegradability and biocompatibility. Toxicology experiments have demonstrated that chitosan has non-toxic effects to the body. These perfect properties make it the most widely used nano- carrier material for nutrients. In our previous study, EGCG is encapsulated successfully within chitosan (CS) - caseinophosphopeptides (CPP) nanocomplexes by a self-assembly method. The nanocomplexes exhibited a good sustained release effect and the CS-CPP nanocomplexes improved the intestinal permeability and absorption of EGCG. Therefore, the bioavailability of EGCG was enhanced through encapsulation by CS-CPP nanocomplexes. However, the biological activity of CS-EGCG-CPP nanocomplexes have not been studied yet. In this study, small angle X-ray scattering (SAXS) was applied to investigate the interaction between CPP and CS. And stability of CS-EGCG-CPP nanocomplexes was investigated in the alkaline environment. In addition, we have studied the anti-oxidant and anti-inflammatory activity of CS-EGCG-CPP nanocomplexes. 1. Preparation, characterization and stability of CS-EGCG-CPP nanocomplexes SAXS is effective in the characterization of the nanocomplexation of the digestied peptides and polysaccharide under the varying pH environments from stomach to small intestine. The change of pH value from 2.0 in stomach to 6.2 in small intestine induced the interaction between CPP and CS, forming the nanocomplexes. The structure parameters changed with the mass ratio between CS and CPP. Fractal dimensions (Df) value of domains inside CPP-CS nanocomplexes is more than 3, indicating the formation of denser particle/aggregate. Df value generally increased with the elevation of CS/CPP mass ratios. The particle size of CS-EGCG-CPP nanocomplexes increases with the elevation of CS concentration and EGCG concentration, however decreases with the elevation of CS/CPP mass ratio. The encapsulation efficiency of EGCG in the nanocomplexes decreases with the increase of CS/CPP mass ratio and EGCG concentration. As CS concentration increases, the encapsulation efficiency of EGCG demonstrates a trend of firstly increasing and then decreasing. The CS-EGCG-CPP nanocomplexes are spherical shape and dispersed uniformly. The average particle size of the nanocomplexes is around 208 nm and the zeta potential of the surface charge (Zeta potential) of the CS-EGCG-CPP nanocomplexes is around +25.6 mV. In addition, CS-EGCG-CPP nanocomplexes can significantly (p<0.01) enhance the stability of EGCG in alkaline environment. 2. Study on the anti-oxidant activity of CS-EGCG-CPP nanocomplexes In the chemical anti-oxidant evaluation system, CS-EGCG-CPP nanocomplexes exhibited similar ability with free EGCG in reduction power, the ferric reducing anti-oxidant power (FRAP), scavenging ABTS radicals and scavenging superoxide anion radicals. Especially, they exhibit much stronger capability than free EGCG in chelating metal ions. At the cellular level, CS-EGCG-CPP nanocomplexes showed the stronger protection against oxidative damage induced by H2O2 in RAW264.7 cells than EGCG. 3. Study on the anti-inflammatory activity of CS-EGCG-CPP nanocomplexes RAW264.7 and Caco-2 cells were induced by LPS to establish the in vitro inflammatory models. The CS-EGCG-CPP nanocomplexes significantly inhibit LPS-induced production of nitric oxide (NO), TNF-α, IL-1β and IL-6 in the RAW264.7 cells. As for the Caco-2 cells model, CS-EGCG-CPP nanocomplexes also significantly inhibit the secretion of TNF-α and IL-8. And the CS-EGCG-CPP nanocomplexes showed stronger inhibition effect on inflammatory cytokines than the free EGCG. We studied the anti-inflammatory mechanism of the CS-EGCG-CPP nanocomplexes through the western blot experiment. The CS-EGCG-CPP nanocomplexes show stronger inhibition effect on the excessive expression of iNOS protein level caused by LPS in RAW264.7 cells than free EGCG. Furthermore, they are showed stronger capacity to reduce expression of phosphorylation and degradation of IκB and translocation of NF-κB p65 than free EGCG, which are mediated by NF-κB signaling pathway. Compared with the free EGCG, the anti-inflammatory activity of CS-EGCG-CPP nanocomplexes was significantly improved.