I assure you, the mugs were absolutely clean 😀.

To the bananas: yes ,there is some justified concern about bananas' polyphenol oxidase (PPO, a ripening enzyme) affects the bioavailability of the polyphenols and specifically of the anthocyanins present in the other fruits.

There are, however, three arguments to mitigate this objection:

first, I also add a dose of ascorbic acid (Vit C) which neutralizes the PPO (I may have forgotten to mention this fact, and will adjust the post accordingly).

Second, PPO's effects do not unfold immediately. If you consume your smoothie within 10 minutes of blending, the effect is negligible (even without the Vit C).

Third, most of the anthocyanins are NOT absorbed as such into the blood stream (typically less than 2% only). Rather is it the metabolic products of anthocyanin digestion through which anthocyanins affect health. It is therefore entirely conceivable that the "digestion" of anthocyanins by PPO outside the body (in your smoothie) does have no or only a negligible effect on their overall health benefits.