乌龙茶粗多酚、EGCG和EGCG3’’Me体外抑制α-葡萄糖苷酶活性

为研究乌龙茶粗多酚、表没食子儿茶素没食子酸酯((-)-epigallocatechin gallate,EGCG)、甲基化EGCG(epigallocatechin3-O-(3-O-methyl)gallate,EGCG3’’Me)对α-葡萄糖苷酶活性的抑制作用,采用酶动力学和紫外吸收光谱方法,探究并比较了三者的抑制活性及类型。结果表明:乌龙茶粗多酚、EGCG和EGCG3’’Me对α-葡萄糖苷酶均有较强的抑制作用,半抑制浓度(half inhibitory concentration,IC50)依次为0.178、0.040、0.064 mg/m L;Lineweaver-Burk双倒数作图显示乌龙茶粗多酚和EGCG的抑制类型为非竞争抑制,而EGCG3’’Me为竞争性抑制;紫外吸收光谱实验表明乌龙茶多酚样品能够使α-葡萄糖苷酶的吸收光谱发生蓝移,推测酶蛋白的构象有所变化。EGCG与EGCG3’’Me对α-葡萄糖苷酶活性的影响和抑制类型的不同可能是由于EGCG的一个羟基被甲氧基取代所引起的。     

The development of a suitable manufacturing process for ‘Benifuuki’ green tea beverage with anti‐allergic effects

Epigallocatechin‐3‐O‐(3‐O‐methyl) gallate (EGCG3″Me) has been reported to inhibit type I allergy better than epigallocatechin gallate (EGCG), a major catechin in tea leaves (Camellia sinensis L). We examined the effects of extraction and sterilization on the catechin content and histamine release from mast cells, as a representative reaction of early phase allergy, in the manufacture of ‘Benifuuki’ green tea beverage. Among various varieties of tea, the cultivar ‘Benifuuki’ contains approximately 2% of EGCG3″Me. Ester‐type catechins and their epimers increased with the increased extraction temperature of the tea. A tea infusion, extracted at 90 °C, strongly inhibited histamine release from mast cells. Furthermore, sterilization affected the catechin content in the manufactured green tea beverage. Sterilization at high temperature promoted the isomerization of catechins and the sterilized green tea beverage had a strong inhibitory effect. When EGCG3″Me, EGCG, epicatechin‐3‐O‐gallate (ECG) and their epimers, GCG3″Me (gallocatechin‐3‐O‐(3‐O‐methyl) gallate), GCG (gallocatechin‐3‐O‐gallate) and CG (catechin‐3‐O‐gallate) were compared, the anti‐allergic effect of GCG3″Me was strongest, and the order of activity was GCG3″Me > EGCG3″Me > GCG > EGCG. We consequently suggest that it was necessary to extract components from tea at the highest temperature possible, and to pasteurize under retort conditions (118.1 °C, 20 min), to manufacture functional green tea beverage with an anti‐allergic action. Copyright © 2005 Society of Chemical Industry     

Flavonoids from a grape seed extract interact with digestive secretions and intestinal cells as assessed in an in vitro digestion/Caco-2 cell culture model

Although the bioactivity of flavonoids is related to their bioavailability, little is known about pre-absorption events in the gastrointestinal tract and their possible interactions with digestive constituents and intestinal cells. Using an in vitro digestion/Caco-2 cell culture model, we investigated the effect of digestive secretions on the stability of (+)-catechin (CAT), (−)-epicatechin (EC) and B2 and B3 dimers from a procyanidin-rich grape seed extract (GSE). The availability of phenolic compounds was not affected by salivary and gastric incubations but decreased during intestinal digestion in the absence of Caco-2 cells due to interactions with pancreatic proteins, unmasked by acetonitrile extraction. Then, in the presence of cells, about 43.9% of CAT, 85.3% of EC and all dimers disappeared at the end of 2 h of intestinal incubation. The stability of all compounds at intestinal pH was demonstrated as well as interactions with proteins, associated with a decrease of some cells enzyme activities, e.g., alkaline phosphatase (−79.8%), sucrase-isomaltase (−60.9%) and aminopeptidase N (−60.7%). Moreover, no compounds were detected in the basal compartment of transwells or in cell monolayers.     

绿茶提取物EGCG对老年痴呆鼠和肥胖鼠的改善作用研究

以老年痴呆症和肥胖症模型小鼠为实验对象,每天用50 mg/kg的绿茶提取物(-)表没食子儿茶素没食子酸酯(EGCG)喂食30 d,分别从实验鼠的外形、生化指标和组织切片等指标进行分析,探讨EGCG对老年痴呆症和肥胖的改善作用。结果表明,EGCG能改善老年痴呆症小鼠大脑认知水平,作用机制可能与脑组织胆碱乙酰转移酶(ChAT)和乙酰胆碱酯酶(AchE)酶活、丙二醛(MDA)含量和β-淀粉样蛋白-42(Aβ42)沉积有关。EGCG具有抑制肥胖功效,其作用机制可能与体内血清脂肪酶和淀粉酶活力有关,影响脂肪和能量代谢。同时,EGCG还具有一定的修复肥胖引起的肝损伤的作用。这一研究成果为绿茶功能食品的开发奠定了理论基础。