Determination of marker compounds to assess the quality of green tea

Green tea, as a commonly consumed beverage worldwide, has a long history of use as a dietary supplement for various conditions. Green tea products have been shown to possess various biological activities, ranging from cardiovascular protection to anticancer effects. The bioactivity of green tea is largely attributed to catechin polyphenols, which make up around on third of the dry leaf weight of green tea. However, the quality of green tea is variable, which may be attributed to the variation in contents of the catechins and other polyphenols, thus the content of these polyphenols may be a suitable determinant of the quality of green tea. The aims of this project are to develop analytical methods to determine the concentration of antioxidant compounds in various green tea products, as well as their antioxidant activities. The findings may be useful for the assessment of green tea product quality and used for quality control of green tea products. Eleven (11) commercial green tea products were sourced from the local market, including dried tea leaves, tea powders and TGA listed tablets and sachet. The green tea products were extracted and subjected to HPLC analysis of selected chemical markers, using a Shimadzu HPLC with a photo-diode array detector, and LC-MS analysis, using a Waters Xevo TQ with electrospray ionisation source and Waters Aquity UPLC. An in vitro DPPH radical scavenging assay was used to determine the antioxidant activity of green tea samples. The total phenolic content (TPC) was determined using the Folin Ciocalteu (FC) method. In addition, an online antioxidant screening assay was developed using HPLC and post column derivatization