Altered senses: advances in sensory science show that genetics and culture dictate taste preferences more than previously believed. As a result, scientists may show that sensory testing will be mind-read predictions instead of a tale told by the tongue

Prepared Foods, August, 2004 by Marcia Wade

Although we commonly use the terms "flavor" and "taste" interchangeably, they mean two very different things. Taste refers to sensations that arise from taste buds in the mouth, which are the standard sweet, salty, sour, bitter and umani.

"Different people have different ways of defining flavor. Our flavor chemists define it as olfactory [or volatile compounds]," says Zata Vickers, a professor in the department of food science and nutrition at the University of Minnesota (St. Paul, Minn.). "Most sensory people define flavor as being a combination of taste plus odor or aroma and the trigeminal sensation."

Flavors or food aromas are chemical combinations perceived behind the nasal passage by retronasal olfaction through the mouth or nose. Chicken, chocolate and butterscotch all are smells. There are no taste receptors on the tongue for those aromas, says Linda Bartoshuk, a professor in otolaryngology (diseases of the ear, nose and throat) at Yale's (New Haven, Conn.) department of surgery. During chewing and swallowing, the air in the mouth is forced up into the retronasal area, where olfactory receptors signal the brain to identify the smell.

No Taste without Smell

"I see the most important development in flavor research as the linkage between smell and taste, and the discovery that smells can enhance taste intensity" states Barry Green, a professor in otolaryngology in the department of surgery at Yale and a fellow at the John B. Pierce Laboratory (New Haven, Conn.). Traditionally, smell and taste were thought of as separate senses that interacted very little. "I think it is going to become more evident that we can modulate taste by the smell route," infers Green.

Historically, scientists believed odors coming in through the nose or the mouth registered in the same way. Research by clinical psychologist Dana Small (Northwestern University, Chicago) has determined that odors are processed in different pans of the brain, depending on their entry point. "The brain is cued as to which way the odor came in," explains Bartoshuk. For example, "If you are sniffing something from the outside world, it's not going to change--no matter what you've got in your mouth."

Retronasal olfaction enhancement for taste only occurs for appropriate, congruent combinations. For example, sweet and pear juice would be fine. However, sweet will not enhance green grass because most people do not eat grass. This stems from the knowledge that humans are not born recognizing odors. Odors are learned by association. "You are not born liking chocolate. You have to learn that," notes Bartoshuk.

"The most profound part of sensory learning occurs prior to four to six months of age," informs Gary Beauchamp, director of the Monell Chemical Senses Center (Philadelphia). "Babies are exposed to what the mother consumes via flavors in her milk, which influences what they will like later." Beauchamp suggests that one of the major factors that differentiates the ethnic groups in terms of their food preferences is due to these early experiences associated with very important emotional and nutritive states that the mother and infant enjoy together.

However, over the last 50 years, the culture has shifted a proportion of our population away from breast feeding to bottle feeding. "What the baby is getting is an extremely bland and absolutely constant set of flavors in [formula]. From a sensory point of view they are missing something," says Beauchamp.

Vickers counts this as important for the food industry because our perceptions of liking foods are not based solely on chemical factors, but also on psychological and environmental influences. For many different reasons, people do not perceive smells the same and, as a result, they do not inhabit the same flavor worlds. Some people are anosmic (exhibiting the inability to detect odors) or have specific anosmias to certain odors. Bartoshuk also suggests that people who have had a lot of ear infections have taste damage, which means the world of taste and aroma is quite different for them.

Flavor in the Genes

On the other hand, "People inherently like sweet and hate bitter, although experience can serve to modulate and overcome some of this," says Beauchamp.

Differences in the central nervous system serve to differentiate taste preferences even more. "The biggest event that has happened in the taste field in the last five years has been the discovery of some of the receptors for bitter, sweet and umami," informs Beauchamp.

Bartoshuk finds a percentage of the population has the ability to taste the bitter compound PROP very strongly. She labels this ability as "supertasting," meaning those individuals have an abundance of a particular receptor in the tongue that is sensitive to PROP and other bitter substances. People who cannot taste PROP or non-tasters, she hypothesizes, are missing a gene for that receptor. Tasters or people who taste PROP--but not strongly--are homozygous for the gene.

According to Bartoshuk, Asians, in general, have fewer non-tasters. "They experience taste (on average) more intensely than do Caucasians. This is probably true for Hispanic and African Americans as well."