There are more catechins in green tea than black tea because of manufacturing process. Green tea contains about 30% catechins, whereas black tea contains only 4% of theaflavins. Both are powerful antioxidants. But green tea has far more in quantity, which explains why it is associated with more health benefits. All types of tea leaves, whether green or black, are from the same tea trees and undergo the same initial preparation processes, but black tea leaves are also allowed to ferment and oxidize. It is thought that these extra preparation steps reduce the amount of antioxidants, making green tea leaves a better source.
Green tea contains six types of catechins: EGCG, EGC, ECG, EC, GC and C. Among the six, there is some evidence that EGCG and ECG are the most potent. However, what makes these catechins important is not their potency, but their abundance. About half of the catechin content of tea is EGCG. Just a small quantity of tea leaves will steep many cups of tea. It is this relative abundance that makes green tea special. No other food or beverage contain this level of antioxidants. EGCG is the focus of many new scientific studies, and has been associated with most of the newly discovered green tea benefits.