Polyphenolic Profile and Antioxidant Activities of Oolong Tea Infusion under Various Steeping Conditions

The phenolic profile and antioxidant activities of oolong tea extract were investigated after tea was steeped in 90 or 100 C water for 3 or 10 min. The extraction yield increased with increasing temperature and extended steeping time. However, higher temperature and longer time (100 C water for 10 min) led to loss of phenolics. The aqueous extract of oolong tea (AEOT) at 100 C for 3 min exhibited the strongest antioxidant activity. The major polyphenolic components of the AEOT were identified as (-)-epigallocatechin (EGC), (-)-epigallocatechin gallate (EGCG) and (-)-epicatechin-3gallate (ECG). The two major catechins (EGC and EGCG) in the tea infusion contributed significantly to the investigated antioxidant activities [i.e., the 2,2-diphenyl-2picrylhydrazyl hydrate (DPPH) radical scavenging and superoxide radical scavenging activities] with high correlation values in r = 0.9486 and 0.9327 for the EGC and r = 0.9592 and 0.8718 for the EGCG, respectively.