Identification Of Pu-erh Old Tree Raw Tea By Infrared Spectroscopy

The price of Pu-erh tea increases with the storage time,and it is difficult to distinguish between new tea and older tea by appearance.In this dissertation,Fourier transform infrared spectroscopy?FTIR?,second derivative infrared spectroscopy?SD-IR?,two-dimensional correlation infrared spectroscopy?2D-IR?)combined with statistical analysis were employed to study Pu-erh old tree raw tea.The results are as follows.The original spectra of Pu-erh raw tea are basically similar,there are some differences in the intensity ratios of several absorption peaks.The absorption intensity ratios of A₁₄₅₁/A₂₉₂₄,A₁₃₆₈/A₁₆₉₇,A₁₁₄₇/A₁₀₃₅,A₈₂₅/A₆₁₀10 and A₇₆₃/A₁₆₄₈648 from Pu-erh area,A₂₈₅₄/A₁₂₃₈,A₁₃₆₉/A₁₆₉₇,A₇₆₃/A₁₆₄₉649 and A₈₂₃/A₆₁₀10 from Xishuangbanna tea area,A₁₄₅₁/A₂₉₂₄,A₂₈₅₄/A₁₂₃₈238 and A₁₁₄₇/A₁₀₃₇037 from Lincang tea area show a decrease trend with the increase of storage year.The ratio of A₂₈₅₄/A₁₂₃₉239 from Pu-erh tea area,A₁₄₅₁/A₂₉₂₄924 and A₁₁₄₇/A₁₀₃₇037 from Banna tea area,as well as A₁₃₆₉/A₁₆₉₇,A₇₆₃/A₁₆₄₉649 and A₈₂₃/A₆₁₀10 from Lincang tea area show an increasing trend with increase storage years.The second derivative infrared spectra of Pu-erh tea was compared with that of standard catechins in the range of 1800-600 cm^-1.It was shown that there were catechins in Pu-erh tea and the absorption intensity and position of each sample were different,and the catechins decreased with the increase of storage years.Two-dimensional infrared correlation spectra of the tea samples in the range of880-1300 cm^-11 and 1300-1700 cm^-11 exhibit obvious differences in the number,position and intensity for auto peaks and cross peaks.The automatic peak number of the tea samples decreased with the increase of storage years.Moreover,The first derivative spectra of 190 samples of 19 kinds of Pu-erh raw tea in the three tea regions were used for principal component and hierarchical cluster analysis.The results show that it can be correctly classified regardless of origin or year.The dissertation work show that Fourier transform infrared spectroscopy,second derivative infrared spectroscopy,two-dimensional correlation infrared spectroscopy combined with principal component analysis and hierarchical clustering analysis method can identify Pu-erh old tree raw tea simply,quickly and non-destructively,and is expected to be developed as a spectral method to identify the origin and storage years of Pu-erh tea.