They have used a group of volunteers for research. After almost a day without eating, they tested sugar, salt and quinine solutions at different concentrations. In concentrations of sugars and salts lower than usual a sweet and salty flavor was detected. However, the bitter taste of quinine was not detected in concentrations lower than saturated.
However, despite being saturated, lower concentrations of quinine are observed, that is, the bitter taste is much easier to detect than salty and sweet.
What the researchers have not yet clarified is what steps the appetite influences: the taste buds of the tongue when taking the stimulus or the brain when interpreting the signal.