| Tea (Camellia sinesis) is one of the most widely consumed beverages in the world. The health promoting effects of tea are generally considered to be associated with its high polyphenolic compounds content. Thus, determination of total polyphenol content (TPC) and evaluation of total antioxidant capacity (TAC) of tea are necessary for better understanding the health benefits in tea.;17 teas were analyzed and compared in our study. Total polyphenol content of tea was measured by the standard Folin-Ciocalteu's method and a new enzymatic method involving the use of horseradish peroxidase and 4-aminoantipyrine, a chromagenic agent. The kinetics and mechanism of five structurally related compounds in enzymatic method were extensively studied by HPLC and LC/MS techniques. In addition, a RP-HPLC method was developed to quantify the contribution percentage of each polyphenolic compound presented in tea. Total antioxidant activity in tea was assessed by oxygen radical absorbance capacity (ORAL), alpha, alpha-diphenyl-beta-picrylhydrazyl (DPPH) radical scavenging and ferric reducing antioxidant power (FRAP) assays. In particular, a rapid, sensitive and convenient SPME-GC-FID method was established to evaluate the capability of selected teas against LDL oxidation. Highest content of polyphenol and strongest antioxidant activity was detected in green tea, followed by oolong tea and then black tea. The pairwise comparisons of the above methods revealed the relationship between total polyphenol content and total antioxidant activity of teas. LC/MS analysis not only help better understanding of the relationship between chemical structure and enzymatic reaction kinetics, but also predicted the potential enzymatic reaction mechanisms of five selected phenolic compounds. Our systematic study on tea will potentially provide innovative applications to the tea-beverage industry. |
