Total Polyphenols in Green Tea Samples by FT-NIR Spectroscopy

摘要

The feasibility of measuring total polyphenols content in instant green tea powder and green tea granules was investigated by Fourier Transform Near-Infrared (FT-NIR) Spectroscopy. The spectra were measured in diffused reflectance mode by keeping 8-10g samples in a small sample bottle. A partial least square regression model was developed with vector normalization as the pre-processing method in the NIR region (4000-12000 cm~(-1) or 800-2500 nm). The developed model was validated using a cross validation technique. FT-NIR Spectroscopy with chemometrics, using PLS - vector normalization as the pre-processing method - could predict the total polyphenols content in tea samples in terms of gallic acid accurately up to an R2 value of 0.978 and a standard error of cross validation (RMSECV) value of 1.45 with 4 factors in the prediction model. The developed model was applied to predict total polyphenols in green tea samples within 30-60 min. The developed procedure was further validated with fresh samples which were not used for calibration and compared with spectroscopic method of ployphenol determination. The overall results demonstrate that NIR Spectroscopy with multivariate calibration could be successfully applied as a rapid method not only to identify tea varieties but also to determine total polyphenols content in green tea samples.