Researchers have found that the enzyme polyphenol oxidase (PPO) in certain fruits like bananas can reduce the absorption of heart-healthy flavanols, especially when combined with flavanol-rich ingredients like berries. The study suggests choosing ingredients with low PPO activity, such as pineapple or oranges, when making smoothies to optimize flavanol absorption.
It’s not a big mystery. Green tea has the most amount flavanols. Fresh leaves also have more compared to aged leaves. Also, powered forms of tea release them more quickly compared to loose leaf. However, you could just steep regular leaf tea for longer as well. The key thing to remember is to not use boiling water, as that may degrade the flavanols, so select a temperature just-below boiling (80-90C / 175-195F).