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

Abstract

The phenolic profile and antioxidant activities of oolong tea extract wereinvestigated after tea was steeped in 90 or 100 oC water for 3 or 10 min. The extractionyield increased with increasing temperature and extended steeping time. However, highertemperature and longer time (100 oC water for 10 min) led to loss of phenolics. Theaqueous extract of oolong tea (AEOT) at 100 oC for 3 min exhibited the strongestantioxidant activity. The major polyphenolic components of the AEOT were identified as(-)-epigallocatechin (EGC), (-)-epigallocatechin gallate (EGCG) and (-)-epicatechin-3-gallate (ECG). The two major catechins (EGC and EGCG) in the tea infusion contributedsignificantly to the investigated antioxidant activities [i.e., the 2,2-diphenyl-2-picrylhydrazyl hydrate (DPPH) radical scavenging and superoxide radical scavengingactivities] 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.

Keywords

• Oolong tea
• Infusion
• Antioxidant activity
• Phenolics