Flavor: Taste and Smell

The senses of taste and smell are closely linked with food-intake behavior, particularly because they are responsible for the perception and enjoyment of foods and beverages. In addition to the pleasure attained from food, the chemosensory systems of mammals provide life-preserving signals to the organism about the chemicals present within the immediate environment. Thus, these systems are vital in determining reproductive success of an organism. Taste, also known as gustation, is a commonly misused term, because when referring to the taste of a chocolate, a piece of cake, or a beverage, most people actually mean overall flavor. Only a small portion (around 5 percent) of overall flavor of foods is actually due to the perception of basic tastes (sweet, bitter, salty, sour, and umami). Flavor is defined as the complex effect of basic taste sensations, olfactory (smell) sensations, and trigeminal sensations (carbonation or the hotness of chili pepper), and textural aspects of food (creaminess, oiliness, smoothness, etc.). Flavor is achieved primarily through the olfactory system (about 95 percent), with only 5 percent attributed to basic taste perception, or the gustatory system. A clear example of this fact is that we often lose the ability to experience the flavor of foods when we have a cold or a stuffy nose. Due to an excess of mucous secretions, olfactory receptors are blocked, thus decreasing the functionality of the olfactory system.

Taste, or gustation, is a sense that involves the detection of the five basic tastes: sweet, salty, sour, bitter, and umami. The umami taste is a savory or meaty taste of L-glutamate, the most common amino acid in proteins, which has recently been added as one of the basic tastes. Umami is a familiar taste in Japanese cuisine, and the discovery of this fifth distinct basic taste was made almost a century ago by a chemist at Imperial University. Some researchers have recently debated that fat, or more specifically, polyunsaturated long chain fatty acids (PUFAs), are also detected by receptors on taste cells. Fat was always thought to be tasteless, and only detectable through the textural components (e.g., creaminess, oiliness) it adds to foods. The discovery of a taste component to dietary fat would add a new complexity to the perception of this nutrient. However, until further research confirms the existence of a “fat taste” mechanism in humans, we remain with the ability to taste five basic types chemicals.

The anatomical features of the taste system consist of taste buds, taste papillae, taste pores, and taste cells. Taste buds are groups of anywhere from 30 to 100 epithelial cells (taste cells) that are often embedded within structural units known as the taste papillae. Papillae consist of three primary types: fungiform, foliate, and circumvallate. The fungiform papillae consist of anywhere from one to three taste buds, and are the large, mushroom-shaped papillae on the anterior surface of the tongue that you can see with the naked eye. The chorda tympani branch of the facial nerve innervates these papillae. Foliate papillae appear as three to four small vertical lines on the side of the tongue. Circumvallate papillae are arranged in a V shape at the back of the tongue. Both foliate and circumvallate papillae are innervated by the glossopharyngeal nerve. At the apex of taste buds, a small pore exists (the taste pore) that extends into the oral cavity, and allows access taste stimuli to gain access to the individual taste cells. These individual taste cells often contain either ion channels or specialized receptors that can respond to the five basic tastes.

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