Abstract: A spectrophotometric method for the determination of tea polyphenols in milk tea powder was developed by using Folin-phenol reagent. Crucial operating parameters such as extraction reagent, number of extraction cycles, temperature and derivatization reagent were investigated. Extraction using 70% methanol solution as the extraction reagent in a hot water bath at 70 ℃ performed twice and oxidization of the resulting extract with Folin-phenol reagent proved optimal. The detection wavelength was selected as 765 nm, and gallic acid was used as the calibration standard for the quantitation of tea polyphenols. The recoveries for whole milk powder spiked at concentration levels of 850–4 500 mg/kg were in the range of 98.9%–104.9%. Good stability and accuracy were achieved. When milk tea powder samples with different contents of tea polyphenols were detected in six replicates, relative standard deviations (RSDs) of 0.29%–0.84% were obtained, indicating good precision. This method proved to be accurate, easy to operate and repeatable with simple and easily available instruments, and thus suitable for the analysis of tea polyphenols in milk tea powder.

Key words: milk tea powder, tea polyphenols, spectrophotometry, gallic acid

摘要： 建立固体奶茶饮料中茶多酚含量的福林酚衍生测定方法。分别考察提取试剂、提取次数、提取温度及衍生试剂关键参数，得出样品中茶多酚用体积分数70%甲醇溶液在70 ℃水浴条件下提取2 次，福林酚试剂氧化提取液，最大吸收波长765 nm，用没食子酸作为校正标准定量检测固体奶茶饮料中的茶多酚。以全脂乳粉为基质进行加标回收实验，当加标量为850～4 500 mg/kg时，回收率为98.9%～104.9%，稳定且准确度良好。针对茶多酚含量不同的奶茶粉进行6 次平行实验，相对标准偏差为0.29%～0.84%，精密度良好。该方法具有结果准确、操作简便、重复性好、使用仪器简便易得等优点，可用于固体奶茶饮料中茶多酚的检测。

关键词: 固体奶茶饮料, 茶多酚, 分光光度法, 没食子酸