THE FUTURE OF FOOD The Science of Yummy

Flavor Basics, Basic Flavors

When you deal with flavor scientists, you have to watch your language. In flavor science, "taste" is only what happens on the tongue-the perception of sweet, sour, salty, bitter and the curious savoriness named umami by the Japanese. But the "flavor" you experience when eating a strawberry, for instance, involves far more than your tongue alone.

Smell is arguably the most vital tool in detecting flavor. The complete list of molecules in a strawberry numbers around 250 compounds, including esters, terpenes and lactones. It takes just four compounds to get your nose to recognize the basic flavor-something like a cheap strawberry candy-but taken alone, they smell nothing of strawberries. One, furaneol, smells like cotton candy. Another, gamma-decalactone, is a creamy peach fragrance. Methyl cinnamate smells like guava, and ethyl butyrate evokes pineapple. A fifth note, cis-3-hexenol, which by itself smells exactly like cut grass, gives strawberry the bright green fragrance of something fresh and alive. There are still 245 other compounds at work in that single berry. (The only two components that your tongue encounters are the sweetness of sugar and the tartness of fruit acids.)

Until the early 1990s, it was generally accepted that there were anywhere from a handful to a few dozens types of odor receptors inside the human nose, each a paired match with a class of molecules. But as the technology of DNA sequencing became widely available, it became possible to discern the underpinnings of scent receptors, gene by gene.

Using DNA analysis on rats and mice, Linda Buck of the Fred Hutchinson Cancer Research Center in Seattle and Richard Axel of Columbia University identified about 1,000 genes-an entire gene family-that code for individual odor receptors in mammals. Of those genes, only 250 to 400 are active in humans, and the overall and active number vary from person to person, giving everyone a slightly different tool with which to experience the world of odor.

To elicit a particular smell-say, that of the aforementioned strawberry-each odor compound activates several receptors (found on the olfactory neurons) in the nose. Further, each olfactory neuron features only one type of receptor, sensitive to only a certain class of molecules. Since all flavors are combinations of aroma molecules, each flavor will create a particular pattern of activated odor neurons in your nose. Your brain recognizes the pattern of activated neurons and tells you that you're smelling a strawberry, and not some other kind of fruit. But because each person's nose has a slightly different constellation of odor receptors, people may perceive a certain scent slightly differently. In 2004 Buck and Axel won the Nobel Prize for Physiology and Medicine for their efforts.