Nontargeted Analysis Using Ultraperformance Liquid Chromatography–Quadrupole Time-of-Flight Mass Spectrometry Uncovers the Effects of Harvest Season on the Metabolites and Taste Quality of Tea (<i>Camellia sinensis</i> L.)

The chemical composition and taste quality of tea fluctuate seasonally. However, the compounds responsible for the seasonal variation of metabolic pattern and taste quality are far from clear. This study compared the metabolite profiles of green teas of nine varieties that were plucked in spring, summer, and autumn by using ultraperformance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS) on a reversed phase column. A multivariate analysis indicated distinct differences among the metabolite phenotypes of teas harvested in different seasons. Heat-map analysis and metabolic pathway analysis demonstrated that flavan-3-ols, theasinensins, procyanidins, quercetin-O-glycosides, apigenin-C-glycosides, and amino acids exhibited sharp seasonal fluctuations. An equivalent quantification of tea tastes showed that in summer and autumn teas, the bitterness and astringency were significantly elevated, whereas umami declined. Metabolite content comparisons and partial least-squares analysis suggested that several flavonoids and amino acids are mainly responsible for the seasonal variations in taste quality.