College of Bioengineering and Food , Hubei University of Technology , Wuhan 430068 , China.
Beijing Advanced Innovation Center for Food Nutrition and Human Health , Beijing Technology and Business University (BTBU) , Beijing 100048 , China.
J Agric Food Chem. 2019 Apr 3;67(13):3744-3751. doi: 10.1021/acs.jafc.8b06681. Epub 2019 Feb 27.
The mechanism of tea-infusion precipitation is not clear. Epigallocatechin gallate (EGCG) and caffeine (CAF) are the core components of green tea infusion precipitate. The critical precipitation concentration ( C) of EGCG-CAF mixed aqueous solutions was assayed through a turbidity assay performed at 25 °C and verified by a differential-scanning calorimeter (DSC) for reliability. Different concentrations of the green tea polysaccharide conjugate fraction (gTPC-D), with a molecular weight of 2.32 × 10 Da, and of metal ions (K, Mg, Ca, and Al) were respectively introduced into the mixed solution to study their effects on C. On the basis of the changed C, the clarification-precipitation phase diagrams of the mixed aqueous solutions were constructed. By calculating the integral area of the clarification phase, it was determined that the four metal ions and gTPC-D could accelerate precipitate formation with a dose-response relationship; among the metal ions, the effect of Al is the strongest, followed by that of Ca.
茶浸出物沉淀的机制尚不清楚。表没食子儿茶素没食子酸酯（EGCG）和咖啡因（CAF）是绿茶浸出物沉淀的核心成分。在 25°C 下通过浊度测定法测定 EGCG-CAF 混合水溶液的临界沉淀浓度（C），并通过差示扫描量热仪（DSC）进行验证以确保其可靠性。分别向混合溶液中引入不同浓度的分子量为 2.32×10 Da 的绿茶多糖缀合物级分（gTPC-D）和金属离子（K、Mg、Ca 和 Al），研究它们对 C 的影响。根据 C 的变化，构建混合水溶液的澄清-沉淀相图。通过计算澄清相的积分面积，确定四种金属离子和 gTPC-D 均可促进沉淀形成，且呈剂量反应关系；在金属离子中，Al 的作用最强，其次是 Ca。
