Quantification of caffeine and catechins and evaluation of bitterness and astringency of Pu-erh ripen tea based on portable near-infrared spectroscopy

Abstract

Rapid and accurate assaying catechins, caffeine, bitterness and astringency prediction are integral to quality assessment and control of Pu-erh ripen tea (PRT). The traditional experimental procedures for content quantification and sensory evaluation are time-consuming and lab-dependent, while near-infrared (NIR) technology has the potential to address this issue. In this work, an efficient and environment-friendly approach was established for caffeine and catechins prediction, and bitterness and astringency evaluation of PRT, using a portable NIR spectrometer coupled with chemometrics. A total of 100 PRT samples were collected for analysis and seven different spectral preprocessing methods and two variable selection algorithms were employed to improve the prediction performance of the partial least squares regression (PLSR) model. The optimized models achieved satisfactory results for the prediction of caffeine and catechins (catechin, catechin gallate, gallocatechin, epicatechin gallate, epigallocatechin, and epigallocatechin gallate), as well as bitterness and astringency, with the correlation coefficient of the prediction set (Rp) above 0.9, and residual prediction deviation (RPD) over 2.5. This research offers an alternative for portable and rapid quantification of caffeine and eight catechins and evaluation of bitterness and astringency of PRT.