Department of Chemistry and Biochemistry, California State University East Bay, Hayward, CA 94542, USA.
Molecules. 2021 Jun 8;26(12):3485. doi: 10.3390/molecules26123485.
The health benefits of green tea are associated with its high catechin content. In scientific studies, green tea is often prepared with deionized water. However, casual consumers will simply use their local tap water, which differs in alkalinity and mineral content depending on the region. To assess the effect of water hardness on catechin and caffeine content, green tea infusions were prepared with synthetic freshwater in five different hardness levels, a sodium bicarbonate solution, a mineral salt solution, and deionized water. HPLC analysis was performed with a superficially porous pentafluorophenyl column. As water hardness increased, total catechin yield decreased. This was mostly due to the autoxidation of epigallocatechin (EGC) and epigallocatechin gallate (EGCG). Epicatechin (EC), epicatechin gallate (ECG), and caffeine showed greater chemical stability. Autoxidation was promoted by alkaline conditions and resulted in the browning of the green tea infusions. High levels of alkaline sodium bicarbonate found in hard water can render some tap waters unsuitable for green tea preparation.
绿茶的健康益处与其高儿茶素含量有关。在科学研究中，绿茶通常用去离子水来制备。然而，普通消费者只会使用当地的自来水，而自来水的碱度和矿物质含量因地区而异。为了评估水硬度对儿茶素和咖啡因含量的影响，用五种不同硬度的合成淡水、碳酸氢钠溶液、矿盐溶液和去离子水制备了绿茶浸提液。采用表面多孔五氟苯基柱进行高效液相色谱分析。随着水硬度的增加，总儿茶素收率降低。这主要是由于表没食子儿茶素（EGC）和表没食子儿茶素没食子酸酯（EGCG）的自动氧化。表儿茶素（EC）、表儿茶素没食子酸酯（ECG）和咖啡因表现出更高的化学稳定性。碱性条件促进了自动氧化，导致绿茶浸提液的褐变。硬水中发现的高碱性碳酸氢钠水平可能会使一些自来水不适合用于绿茶的制备。
