Interrelation analysis between phenolic compounds and in vitro antioxidant activities in Pu-erh tea

Pu-erh tea is a Chinese dark tea produced by sun-dried green tea-leaves. In this study, 17 phenolic compounds and 3 purine alkaloids in 36 Pu-erh teas were determined by high-performance liquid chromatography. Additionally, the in vitro antioxidant activities were evaluated by 5 various assays, respectively. PCA, HCA and OPLS-DA (R2X = 0.639, R2Y = 0.945 and Q2 = 0.940, respectively) could divide into fermented Pu-erh tea (FPT) and non-fermented Pu-erh tea (NFPT) groups absolutely. Compared with NFPT, solid-state fermentation caused the extremely significant (p < 0.001) decreases of 8 catechins, 3 other flavonoids (i.e. taxifolin, rutin and luteolin), gallic acid (GA), hydrolyzed tannin and theophylline, and enhanced ellagic acid, kaempferol and quercetin contents significantly (p < 0.05, <0.01 or <0.001) in FPT. Bivariate correlation analysis confirmed that 8 catechins, 3 flavonoids, theophylline and GA promoted the antioxidant activities of Pu-erh teas, while queretin showed extremely significantly (p < 0.001) negative correlation to the results of DPPH, ABTS and HSA assays. Furthermore, multivariate linear regression equations efficiently evaluated the results of FRAP, DPPH, ABTS and HSA assays in Pu-erh tea with a R2 value over 0.95. This study elaborating the interrelation between phenolic compounds and in vitro antioxidant activities advanced the knowledge about Pu-erh tea.