Untargeted and targeted metabolomics reveals potential marker compounds of an tea during storage

Abstract

An tea (AT) is a dark tea with a unique flavor that affects the quality of storage time. However, changes in the sensory quality and chemical composition of AT during storage are unknown. The present study performed sensory evaluation and metabolomic analysis of AT at seven storage time points. The results indicated that the tea liquor color changed from orange to dark red during storage, and the astringency intensity gradually decreased concomitant with the appearance of a stale taste. Seventy differential metabolites were identified by untargeted liquid chromatography coupled with mass spectrometry (LC–MS) including catechins, flavonols and their glycosides, free amino acids, alkaloids, and phenolic acids and their derivatives. Targeted analysis demonstrated that quercetin, quercetin 3-O-glucuronide, quercetin 3-O-rutinoside, glycine, aspartic acid, alanine, serine, arginine, threonine, tyrosine, theanine, GABA and isoleucine were highly correlated with storage time (r < −0.8 or r > 0.8). Furthermore, linear regression analysis confirmed that these 13 substances were good predictors of AT storage time (correlation coefficient of 0.8767). The present study reveals the changes in the components during storage of AT and provides a theoretical basis for quality improvement of stored dark tea.