Compositions and Antioxidant Activities of Oolong Tea Extracts Made by Two Processing Methods

An aromatic oolong tea was used as the raw material to extract polysaccharides (TPs) and other constituents (TPs-A, TPs-B and TPs-C) using two processing methods. The chemical compositions, reducing power, and DPPH scavenging capacities of the extracts were determined. The results showed that the method applying 65% ethanol for pre-soaking followed by a water extraction (E-W) produced more TPs and less soluble protein than the process employing a water extraction before precipitation by 65% ethanol (W-E). E-W promoted the extractions of polyphenols, catechins, flavonoids and caffeine; while, W-E was less efficient in separating or concentrating the components. On the antioxidant activity, TPs obtained by both methods were significantly lower on the reducing power and DPPH scavenging capacity than those of TPs-A, TPs-B and TPs-C. The correlation analysis suggested that the antioxidant activity of TPs was significantly related to the contents of polyphenols, catechins, and particularly ester catechins in the extract.There was also a synergism among TPs, total flavonoid and caffeine. It appeared that as antioxidants, TPs exhibited significantly lower activity than the phenolic compounds in the tea.