Bitter taste protects us from ingesting poisons - that's the best guess of those who study our taste perceptions from a genetic standpoint. Most poisons are heavy alkaloids which taste bitter. Bitter receptors are primarily located at the back of the throat, the "last stand" until food or whatevers in your mouth starts down the hatch and it's the most sensitive of the five basic tastes. We can detect it a very low levels. It's a protective mechanism. Great design.
Some foods with acceptable bitter properties are coffee, tea, some greens, citrus peel, tonic water, angostura bitters, endive, radicchio. We expect bitterness in the flavor profile and so we don't react as we would to the presence of a "foreign" bitterness. Those who are super-sensitive to bitterness experience the taste in beet greens, chards, bok choy, most cabbages and Brussels sprouts.
While there is a big market in no calorie or low calorie or no sugar added food products, the largest application for bitter blockers is likely in the pharmaceutical area. Making medicine taste better and therefore more palatable is what most of the research is striving for.
I loved this tongue twister as a kid.
Betty Botter bought some butter,
"But," she said, "this butter's bitter.
If I bake this bitter butter,
It will make my batter bitter.
But a bit of better butter -
That would make my batter better."
So she bought a bit of butter,
Better than her bitter butter,
And she baked it in her batter,
And the batter was not bitter.
So 'twas better Betty Botter
Bought a bit of better butter.
Happily butter is rarely if ever bitter - at least in my experience. We're getting it all these days from the Reb A. We're having to take the bitter with the sweet.