Determination of Catechins and Caffeine Content in Tea (Camellia sinensis L.) Leaves at Different Positions by Fourier-Transform Infrared Spectroscopy

In new shoots, the contents and distribution of catechins and caffeine, two important bioactive chemicals in tea ( L.), strongly reflect the physiology and nutrition of tea. In this study, four primary catechin monomers and caffeine in tea leaves at different positions on three cultivars were determined by Fourier-transform infrared (FTIR) transmission spectroscopy coupled to chemometrics. A combination of interval partial least squares (iPLS), competitive adaptive reweighted sampling (CARS), and successive projections algorithm (SPA) was used to extract characteristic wavenumbers that reflected the molecular characteristics of the constituents. Furthermore, Gaussian process regression (GPR) determination models were developed for all constituents with good predictability and robustness based on the extracted wavenumbers. The coefficients of determination for the prediction sets were all approximately 0.93, which indicated the high feasibility of FTIR spectroscopy for determination of catechins and caffeine in tea leaves. This analytical method could provide quick and efficient detection of catechin monomers and caffeine in fresh tea leaves, which have great impacts on the cultivation of tea trees and the selection of raw materials for tea processing. Keywords: Caffeine, Catechin, FTIR spectroscopy, Gaussian process regression, Quantification, Tea.