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.
So basically, just add a bit of lemon juice to your smoothie?
I’m not confident saying for sure without reading the actual paper - it really depends on how PPO interacts with the flavanols, but at the end of the day denaturing the PPO with heat should make it a non-issue. Keep in mind though that bananas are far from the only smoothie ingredient with PPO!
Or add cooked banana instead? Heat it up before freezing that over ripe banana.