Taste Stimuli: Chemical and Food

In the lexicon of the consumer, taste refers to the entire sensory experience of a food or beverage. Thus, it includes visual sensation. Is the cola beverage brown like it should be? Are the grapes the right size and without deformities? It also includes auditory sensation. Does the apple crunch when biting into it? Does the carbonated beverage fizz when pouring? And it includes tactile sensation. Is the banana firm or is it soft? Is the milk shake thick and rich, or is it thin and watery? Olfactory sensation is a major contributor to food and beverage perception and is more confused with taste than any of the foregoing. But really, taste is a gustatory sensation. It emanates from specialized sensory cells of the taste buds located on the tongue and some other parts of the oral cavity. All of the other four senses contribute significantly to the overall perception of foods and beverages but are not taste. Only gustatory sensation is taste.

Gustation is constituted of the four well-known primary tastes: sweet, bitter, sour, and salty, and one lesser-known taste known as savory, but often referred to as umami, the Japanese word for delicious. The stimuli initiating these tastes are all chemical compounds occurring naturally in foods and beverages. For the case of sweet taste, due to health issues associated with diabetes and obesity, noncaloric sweeteners are now in use, as well as the common caloric sweeteners.

Many protocols have been employed in the sensory testing of chemical compounds. In order for a compound to have taste, it must be soluble in water and saliva. If a solid chemical is tasted, its taste will be dependent on its rate of dissolution in saliva, a variable that is difficult to control (i.e., dependent on solid particle size, crystal form, level of agitation of the solid/saliva mixture, etc.), and therefore sensory testing is not generally carried out with solid samples. At the same time, however, in real life, consumers often experience solid stimuli in the course of normal eating. Nonetheless, in almost all cases, sensory studies on gustatory stimuli are carried out on prepared solutions with known concentrations. In other cases, where this is not possible, stimuli concentrations are determined by chromatographic or spectroscopic methods. This entry describes sweet-tasting, bitter-tasting, umami-tasting, sour-tasting, and salty-tasting stimuli, as well as stimuli exhibiting mixtures of primary taste qualities.