Black tea mouthfeel characterisation by NMR analysis and chemometrics

Abstract

The molecular understanding of black tea mouthfeel has been hindered by the difficulties of complete separation and identification of its constituents. The aim of the current work is to better understand the contribution of the whole non-volatile matrix of black tea to its in-mouth sensation, with a focus on astringency. Eight single origin black teas from different parts of the world were studied. 1H NMR data were acquired directly from the tea infusion. Descriptive analysis of the aroma and in-mouth characteristics of the tea infusions was carried out by a trained sensory panel. Significant differences were found among the teas for astringency. The NMR spectra were used as predictors of the intensities of the astringency attribute using PLS models. Prediction errors calculated through cross validation were smaller for the models constructed with a single interval of the spectrum, rather than the total spectrum. In turn, models that included combinations of spectral intervals resulted in shorter prediction errors. The zones of the NMR spectra of highest contribution to the predicted astringency were those that contained signals from gallated species, caffeine and aliphatic methyls from low-level constituents.