Effect of different storage years on the quality of unzymic and zymic Pu-er tea by FTIR combined with feature extraction

In this paper, Fourier Transform Infrared Spectroscopy(FTIR) combined with feature extraction was used to study unzymic and zymic Pu-er tea for different storage years, including 6 kinds of zymic tea and 2 kinds of unzymic tea. The result indicated that the absorption peaks of unzymic and zymic Pu-er tea had the tendency to decrease while the storage times prolonged. Compared to the tea for 1 year, the change of unzymic Pu-er is stronger than that of zymic Pu-er. Using the characteristic extraction process, projection offset of various kinds of tea on the projection score can be obtained. The projection offset of unzymic and zymic Pu-er were 10.0-14.2 and 1.7-4.3. The result showed that the former is far more than the latter. It is due to different proportion of chemical constituents exists in unzymic and zymic Pu-er tea, such as alkaloids and phenolic compounds. This study presents the certain scientific bases for investigating the effect of different storage years on the quality of unzymic and zymic Pu-er and storing efficiently.