結合茶品單寧及胺基酸含量檢測之螢光流動注射分析系統

Abstract

本研究開發一套整合單寧與胺基酸含量檢測之螢光流動注射分析系統，檢測原理分別為單寧對3-aminophthalate螢光團之螢光消光特性與鄰苯二甲醛 (o-phthalaldehyde, OPA)和胺基之螢光生成反應。由於兩者均有相同之激發波長(340 nm) 和接收波長 (425 nm)，故可在同一台偵測儀器、同一套系統流路之檢測環境下依序檢測茶品中之單寧及胺基酸含量，開發一套簡便之線上茶品檢測系統。文中探討樣品注射體積、反應流路長度、OPA濃度、2-mercaptoethanol濃度及溶劑pH值等系統參數之最適化情形，並確認單寧酸溶液對OPA試劑之干擾情形與四種主要胺基酸之相對螢光發光響應。本系統對單寧酸和茶胺酸之檢量範圍分別為 50-250 μg mL-1以及0.1-1 μg mL-1，CV 值小於5 % (n = 3)，檢測速度為每小時20個樣品。本系統應用於台茶12號所製作之包種茶，探討製造過程中包括茶葉採摘條件、萎凋時間、冷泡茶方法等變因對茶湯內單寧與胺基酸含量之影響。本研究尚針對四種不同市場價格之台灣烏龍茶進行含量檢測，並與其市場價格進行初步分析探討。

A fluorometric flow-injection analytical system for determining both tannin and total amino acid content is proposed. The sensing principles are based on the quenching effect of tannin on the fluorescence of 3-aminophthalate and the fluorogenic reaction of amino acids with o-phthalaldehyde (OPA), respectively. Both reactions were integrated into a fluorometric flow-injection system with the same excitation and emission wavelength (340/425 nm). A three-way valve was introduced to switch between the reagents for sequential determination of tannin and amino acids. Parameters of operation condition were optimized, and interference of tannic acid on the fluorescence intensity of OPA-amino acids reaction was investigated. The linear dynamic range for tannic acid and theanine were 50-250 μg mL-1 and 0.1-1 μg mL-1 (CV < 5%, n = 3), and the sample throughout was 20 samples h-1. Effects of plucking position of tea plants, withering time and steeping method on tannin and amino acids in consumer tea brew of Pouchong tea in Taiwan were analyzed by the proposed system. Analytical results of commercial oolong tea products in Taiwan were compared to their market prices.