- The Washington Times - Thursday, June 14, 2007

n allergy or summer cold might make food taste bland, but the sense of taste has little to do with the change.

“Colds affect flavor, which is a combination of taste and smell and mouth feel,” says Paul Breslin, a member of the Monell Chemical Senses Center, a research institute in Philadelphia focused on interdisciplinary research, training and communication about taste and smell. He holds a doctorate in experimental psychology.

“You can still taste things, but you lose the ability to smell. Taste and smell integrate in the brain to come up with a unified sensation we call flavor,” Mr. Breslin says.

Flavor, he says, is not the same as taste because the aroma of a food is combined with taste to give thousands of flavors. Flavor derives, in part, from the temperature, texture and sensations in the mouth that come from a food or beverage, he says.

“When you don’t smell, you lose a major part of flavor,” Mr. Breslin says.

Taste — one of the five senses — is largely dependent on the sense of smell, says Dr. Jean Kim, otolaryngologist at the Johns Hopkins School of Medicine in Baltimore.

“If your sense of smell is diminished, your sense of taste is going to diminish,” Dr. Kim says.

Taste occurs when special sensory cells located in the tongue, throat and cheeks respond to the five basic taste qualities, that of sweet, sour, bitter, salty and savory or umami, says Barry Davis, director of the taste and smell program at the National Institute on Deafness and Other Communication Disorders, a part of the National Institutes of Health (NIH) in Bethesda. He holds a doctorate in neuroscience.

“When you chew food, it releases aromas … that enter the olfactory system and contribute to the flavor of food,” Mr. Davis says.

Taste buds have about 100 taste cells, which have receptors attuned to one of the five taste qualities, Mr. Davis says. Tiny pores at the tip of each taste bud allow chemicals in food and beverages to enter the taste cells, he says.

“In a very real sense, your taste cells are exposed to the outside world,” Mr. Davis says.

Humans have about 10,000 taste buds, as stated in a “Taste Primer” information sheet provided by the Monell Chemical Senses Center.

A common misconception is that these taste buds are located on the tongue only, but they are located throughout the mouth, including the palate, throat and cheeks, Mr. Davis says. Another misconception is that different areas of the tongue can detect certain taste qualities, but each taste cell has receptors attuned to one of the five taste qualities, he says.

“You take these thousands of cells customized and specialized to one of the taste qualities, and you spread them over the mouth,” Mr. Davis says. “The tip of the mouth is not just for sweet, but your whole mouth becomes sensitive to it.”

When taste receptors recognize the taste stimuli, chemical signals are sent from the taste receptor cells to neurons in the brain to distinguish taste quality, Mr. Breslin says.

“Taste is ultimately done in the brain,” he says. “The brain’s interpretation of the signals helps us taste.”

The ability of taste cells to respond to different taste qualities is, in part, genetically determined, Mr. Davis says. In other words, genetics help determine how sensitive taste cells are to taste qualities, he says. The cells for detecting bitter and sweet tastes, for example, are not the same for everyone and range in ability from low to high, he says.

Other variables that contribute to taste include how well food is chewed and the quality of the oral environment, such as good or poor oral hygiene, Mr. Davis says.

“Our brain has specialized in taking on inputs from the nose and mouth and [combining] them into a single perception,” Mr. Breslin says.

When sense of smell is diminished, possibly from a cold or health problem, the sense of taste is not lost and remains able to indicate a food’s sweetness, bitterness or the three other qualities, Mr. Breslin says.

“You say you can’t taste the food,” he says. “You don’t really mean taste. Taste is vernacular or shorthand for all of these sensations that come together to give us flavor.”

The aging process causes the sense of smell to diminish significantly more than the sense of taste, though loss of taste is given the blame, Mr. Breslin says.

“Because of that, your enjoyment of food decreases. You lose the ability to detect the flavors of food, and food becomes bland,” Mr. Davis says.

Thirty percent of Americans between the ages of 70 and 80 and two out of three Americans older than 80 experience problems with their sense of smell, according to information provided on the NIH Web site (www.nia.nih.gov). A decrease in sense of smell can lead to weight loss or weight gain from not eating enough or eating too many fatty foods. Compensating for loss of smell and taste by adding sugar and salt to foods also can cause problems for people with heart disease, diabetes, stroke and other illnesses requiring a specific diet, the Web site says.

The sense of smell can be affected by head trauma, sinus and viral infections, use of certain medications, and some diseases, such as sinus disease and neurodegenerative diseases, Dr. Kim says.

Losing the sense of smell is an important sensory loss because smell, along with taste, is used to identify inedible, spoiled foods and beverages.

“Certain smells can ward us off and tell us of danger. Taste can help us interpret our environment,” Dr. Kim says.

Total loss of taste is a rare disease, and having a taste problem is uncommon, Mr. Davis says.

“People call taste and smell the minor senses,” he says. “A lot more is known about hearing and vision. The amount of research and clinical work and our understanding of the taste system is considerably less than that for the smell system. … People don’t die from a taste problem or from a smell problem.”



Click to Read More

Click to Hide