A new strategy for grading of Lu'an guapian green tea by combination of differentiated metabolites and hypoglycaemia effect.

Predictable tea grading bears not only scientific merit, but also commercial value. Lu'an guapian green tea (LGGT) is one of the most famous green teas in China. Based on morphology and sensory flavour, LGGT was traditionally graded as first premium (FP), second premium (SP), first grade (FG), second grade (SG), third grade (TG) and summer grade (SuG). The chemical profiles and distinct metabolites distinguishing different grades of LGGT are yet to be defined, neither the grade related health benefits be evaluated. In present study, non-targeted metabolomics combined with chemometrics analysis showed that FP and SP, FG and SG exhibited high similarity, respectively. TG and SuG both exhibited great difference from the other grades. Therefore, LGGT could be regrouped into four grades. Furthermore, eight metabolites were identified and displayed grade related bio-markers of LGGT, which are gallic acid, catechin, gallocatechin, salicylic acid, theasinensin B, theasinensin C, kaempferol 3-(6''-rhanmnosylsoporoside) and l-linalool 3-[xylosyl-(1->6)-glucoside]. Quantitative analysis further confirmed that gallic acid, catechin, gallocatechin and salicylic acid were distinct grade-related metabolites. In vitro and in vivo data showed that methanol-extracts of higher grades LGGT exhibited more potent α-amylase and α-glucosidase inhibitory activity and hypoglyceamia effect than that of lower grades.