Pineapple can reduce or eliminate the bitterness of ampalaya. I’m not sure about it. It’s just a hearsay. No scientific basis.
Ampalaya is bitter because a certain substance, as stated here, “Ampalaya is Bitter Because of Alkaloid Momordicine“.
I setup a simple experiment without reading related articles from the world wide web. I never bought the two commodities just for the sake of test. I waited patiently for this rare opportunity. The availability of both amplaya and pineapple in house.
How can pineapple reduce or eliminate the bitterness of ampalaya? Maybe the first has some sort of enzymes that react to momordicine, the likes of papain that can soften tough meats.
I grabbed a piece of ampalaya while my wife was preparing a meal for lunch. I sliced it thinly then soaked in pineapple juice. I waited one hour and had a taste. The taste became slightly less bitter. Waited more hours but it never became significantly less bitter.
The verdict. Pineapple cannot remove ampalaya bitterness. The principle is similar to adding sugar and other spices to ampalaya dish. Ampalaya when eaten with pineapple slices, the sweet and sour taste tend to mask the bitterness. It can mask but cannot remove the bitter substance completely.