Influence of preparation procedures on the phenolic content, antioxidant and antidiabetic activities of green and black teas

The influence of common tea preparation procedures (temperature, infusion time, consumption time interval and tea bag/loose-leaf) and the type of water used, on the total phenolic content (TPC), the radical scavenging activity and the α-glucosidase inhibitory activity were assessed. Higher TPC and antioxidant activity were obtained when using lower mineralized waters. Tea bags also evidenced higher antioxidant activity than loose-leaf samples. Under the same conditions (90 ºC and five minutes of infusion time) green tea contains almost twice the quantity of polyphenols and the free radical scavenging ability of black tea. In the α-glucosidase assay all infusions were active (97-100 %). Furthermore, HPLC allowed to identify some of the polyphenols present in both teas and to monitor their composition change with time. After twenty-four hours, the antioxidant activity was maintained without significant changes, but a small decrease in enzyme inhibition was observed, although this activity was still very high.本研究评估了常见茶叶冲泡流程（水温、浸泡时间、饮用时间间隔、茶包/散茶形态）与用水类型对总酚含量（TPC）、自由基清除活性及α-葡萄糖苷酶抑制活性的影响。实验结果表明，使用低矿化度水体时，茶样的总酚含量与抗氧化活性更高。相较于散茶样品，茶包的抗氧化活性同样更优。在90℃、浸泡5分钟的相同条件下，绿茶的多酚含量几乎为红茶的两倍，且其自由基清除能力优于红茶。在α-葡萄糖苷酶活性检测中，所有茶浸液均表现出抑制活性，抑制率介于97%~100%之间。此外，本研究通过高效液相色谱（HPLC）鉴定出两种茶叶中含有的部分多酚类物质，并监测了其组分随时间的变化趋势。静置24小时后，茶浸液的抗氧化活性未发生显著变化，但酶抑制活性出现小幅下降，不过该活性仍维持在较高水平。