Thanks, Tom, for your contribution and your thoughts on the banana ingredient. I'm aware of the issue, but it needs a little more context. Yes, banana polyphenol oxidase (PPO) has an inhibitory effect on the bioavailability of phenolic contents of fruits mixed with banana. On the other hand, the gastric digestion of banana itself more than doubles the bananas' antioxidant capacity compared to the antioxidant content in the ripe fruit itself. Since we are after the antioxidant capacity of our smoothie intake, the jury is still out about the true net effect. But you might be on the safe side of the issue by consuming your smoothie separately from the bananas. I try to limit the PPO's effect on the flavonols by (a) adding citric acid, an inhibitor of PPO acitiviy, and (b) consuming the drink right after the blending process. The PPO activity within the first 10 minutes of preparation is much less. In essence, though, the effects of PPO on concomitant flavonoids is probably a real issue in ready-to-consume commercial preparations. You might be better off choosing concoctions that do not contain banana or beet leave extracts, the latter having comparably high PPO activity, too.