How could I easily quantify the amount of EGCG in a sample of green tea? I am currently conducting an experiment to study the effects of pH on the rate of thermal decomposition of Epigallocatechin Gallate (EGCG) in green tea.

One of the key steps in my procedure is quantifying this EGCG content in the green tea. What are some of the methods which I could use to determine and quantify this EGCG content?
To analyze specifically this component, you will have to use HPLC. 
In case you can use a more generic approach, you can analyze the total phenolic content with the Folin-Ciocalteu method. 

The Folin-Ciocalteu method is based on a reaction with polyphenols that gives a blue color. 
This color can then be measured in a UV-Vis spectrophotometer and the concentration can be established. 

This method has been used to quantify polyphenols in many plants, as for example here.