Fig. 1
![Fig. 1](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs41702-020-0057-8/MediaObjects/41702_2020_57_Fig1_HTML.png)
Structural formula of eight catechins. Catechins have many chemical structural features, such as hydroxyl groups (–OH), that combine easily with other materials. There are eight catechins: C ((-)-catechin), EC ((-)-epicatechin), ECG ((-)-epicatechingallate), EGC ((-)-epigallocatechin), EGCG ((-)-epigallocatechin gallate), GC ((-)-gallocatechin), CG ((-)-catechingallate), and GCG ((-)-gallocatechingallate). The principle types are C, EC, ECG, EGC, and EGCG