以氧化還原電位評估臺灣精品茶抗氧化特性之研究

Electrochemical Evaluation of Antioxidant Properties of Taiwanese Boutique and Aged Oolong Teas in Terms of Oxidation-Reduction Potential

茶葉的組成中含有大量的多酚類化合物，具有良好的電化學活性，因此有利於應用電化學技術對茶湯的組成進行分析，其中氧化還原電位（oxidation-reduction potential, ORP）是一種簡便的量測工具，採用白金片/氯化銀參考電極之二極式量測裝置，或僅需使用一個特製的複合電極，即可快速讀出該系統的氧化還原電位值。
本研究以赤血鹽/黃血鹽氧化還原法驗證了以能斯特方程式測量氧化還原電位系統的可靠性。接著我們對多種茶湯樣品進行ORP值的測量，這些樣品包括來自同一年度（2022年）的七種台灣特色茶（Taiwan boutique teas）以及五種不同年份的烏龍陳茶（Oolong aged teas）。此外，研究進一步對高山烏龍茶在不同沖泡條件下（包括茶葉量、溫度、沖泡次數和隔夜茶）的茶湯進行了氧化還原電位值的測量，以探討臺灣茶茶湯的氧化還原特性。最後結合七種地方特色茶的ORP量測結果，對樣品進行DPPH檢驗，藉此探討各種特色茶湯的清除自由基能力，並進一步瞭解其與特色茶的ORP值之間的關聯。
研究結果發現，七大特色茶類的ORP值與茶品的發酵度高度關聯，而文山包種茶和碧螺春具有較低的ORP值。不同茶乾添加量對茶湯ORP的量測結果顯示，增加沖泡的茶葉量，可有效降低茶湯的ORP初始值。由1.5g（最低茶葉量）的2.6mV，最後降低至6g（最高茶葉量）的-117mV。若干茶飲愛好者認為第一泡茶最好喝。本研究對不同沖次茶湯的ORP值量測結果顯示：每一沖的ORP值都是負值。各沖次的ORP值比較結果（由低到高）分別為：第二沖、第三沖、第四沖、第一沖。
七種台灣特色茶的DPPH檢測結果證明其數值高低與氧化還原電位值相關，顯示ORP與清除自由基的能力相關，間皆指出ORP值與各種茶類抗氧化能力的強弱可能有關。

Tea contains an abundance of polyphenolic compounds, which endow it with high electrochemical activity. The present study electrochemically investigated the antioxidant properties of Taiwanese boutique teas（seven species of specialty tea and five varieties of aged oolong tea）in terms of the oxidation–reduction potential（ORP）values of as-brewed tea infusions. Experimental values were referenced against a linear relationship ORPµln[Fe（II）]/[Fe（III）] derived from the Nernst equation.
In each variety of tea, the ORP was highly correlated with the degree of tea fermentation, and Wenshan Baozhong tea and Biluochun tea had the lowest ORP values. The number of tea leaves added per pot of brewing tea was correlated with the ORP of the resultant tea infusion. As the weight of tea leaves increased from 1.5 to 6.0 g per infusion, the ORP decreased from 2.6 to−117 mV. Finally, the number of infusions also strongly affected ORP. For all teas, the ORP was highest at the first infusion, lowest at the second infusion, and increased with every subsequent infusion after the second. Traditional Chinese beliefs indicate that tea left standing overnight is undesirable to drink. Results from a DPPH test demonstrate that the aforementioned ability to scavenge free radicals is attributable to the redox potential value, which can reflect the antioxidant capacity of various teas.