Distribution of free, esterified, and insoluble bound forms of phenolics in tea seeds and their antioxidant activity.

In this study, phenolic compounds in their phenolic extract (PE), free phenolic (FP), esterified phenolic (EFP), and insoluble bound phenolic (ISBP) forms were extracted from tea seeds and quantified using HPLC to obtain information on the phenolics that are present in tea seeds along with their antioxidant activities. The total phenolic content of the ISBP fraction was higher than that of the FP and EFP fractions. The phenolic acids in tea seeds exist either in esterified or glycosided forms. Moreover, hydroxycinnamic acid derivatives have been identified as important phenolic acid components in tea seeds. The ISBP fraction was an effective antioxidant based on the results obtained from the in vitro assays performed, which include the DPPH and 2,2-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)-derived nitrogen-centered radical scavenging activities, Fe3+-2,4,6-tripyridyl-s-triazine reducing ability, as well as Cu2+ and Fe2+ ion chelating effects.