If you break it down far enough, sweet salty bitter and sour describe more than you expect.

Sweet is saccarides and the like.

Salty is ionic compounds.

Sour is acids

Bitter is bases.


I think the amount of Protein is texture. Fats is dryness and amount of flavor.

Your taste buds have a lock and key system similar to enzymes, so different shaped particles trigger different buds. Fats also help the particles get into the buds, enhancing flavor.

Different areas of the tongue do have higher amounts of certain receptors, but because of the moist environment, it is difficult to keep food in one place.