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WHY YOU LIKE BROCCOLI:
Your genes told you to // Your mother ate it while pregnant // Grandma’s broccoli au gratin was irresistible // A combination that might someday allow others to like it too

A Matter of Taste

By Cathryn Delude // Photographs by Levi Brown // Spring 2012
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Levi Brown

How people perceive and respond to the taste of food is largely a matter of evolution. We’re born loving sugar because it signals the presence of carbohydrates that fuel the body. We want salt because it maintains our cells’ electrolyte balance. Savory alerts us to amino acids, the building blocks of proteins. Bitter warns against ingesting toxic, noxious chemicals in plants, and sour saves us from spoiled, fermented food. Yet not all tasters get the same message. John Hayes drinks unsweetened black coffee but shuns grapefruit. His wife loves grapefruit but abhors black coffee. Their daughter likes both and sometimes prefers grapefruit to cheesecake.

Hayes is director of the Sensory Evaluation Center at Pennsylvania State University, and based on his research, he thinks he can relate those varying preferences to underlying biological differences in how tongues detect bitter compounds. Such innate variations, mostly determined by a person’s genetics, affect how responsive taste buds are to particular food molecules, as well as how many taste buds there are, and so how strong a signal they send to the brain. Varying perceptions of the five basic tastes—bitter, sweet, salty, sour and savory (or umami, a Japanese word for “delicious”)—affect food likes and dislikes, which influence our food choices.

Inborn attractions and aversions served humans well when the most important thing was getting enough food and not being poisoned by it. Yet our needs have evolved, and it would be ideal now if taste encouraged healthy food choices—rather than pushing people away from broccoli, for instance, which some find repulsively bitter, or drawing us to fattening sweets and carbohydrates. Indeed, bitter compounds also contain beneficial vitamins, antioxidants and flavonoids.

Scientists have only recently begun to understand how the tongue, much less the brain, responds to taste and how genetic variations affect its response. Now, as they trace connections among taste, flavor and food choices, they’re finding that people’s innate predispositions don’t always predict which foods they will actually like or dislike, and that environmental factors, including a mother’s choices passed along in amniotic fluid, also play a role. As researchers parse the interplay of all of these factors and their impact on health, some are looking ahead to a time when it may be possible to entice people toward foods they are hardwired to avoid and away from others they enjoy to an unhealthy extreme.

A large part of the gustatory system, which governs what and how we taste, is visible on any human tongue. There are small, mushroom-shaped structures called papillae that contain globular clusters of taste buds. Each taste bud in turn has 50 to 150 taste cells, each of which is studded with proteins known as chemoreceptors that detect only one of the five tastes. Chemoreceptors bind to a specific type of food chemical, variously known as a tastant, taste stimulus or ligand. For example, natural sucrose and similarly shaped molecules in artificial sweeteners are tastants that connect to sweet receptors, and when they make their wonted links, they trigger a reaction that sends a signal of sweetness to the brain. That message travels along a cranial nerve from the tongue to the medulla, in the brain stem, which connects to other brain regions involved in appetite, emotion and cognition.

Scientists knew much less about the physiology of taste 80 years ago, when DuPont chemist Arthur L. Fox made an accidental discovery. Fox was transferring a newly synthesized compound, phenylthiocarbamide, or PTC, to a container, and some of the powder wafted into the air. A colleague tasted something horribly bitter, but Fox detected nothing. Curious, he gave samples to other people, most of whom also thought it ghastly. But about a quarter of them, like Fox, found it tasteless. Fox and geneticist A.F. Blakeslee then took PTC to a scientific meeting and observed a 2.3-to-1 ratio of tasters to nontasters—close enough to the 3-to-1 inheritance pattern of dominant to recessive characteristics, as with Gregor Mendel’s peas, to indicate that nontasting was a recessive trait.

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Could It Taste as Sweet?

New compounds that realign perceptions of sweetness and bitterness are nearing the marketplace.

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hed-dossier

1. “Common Sense About Taste: From Mammals to Insects,” by David A. Yarmolinsky, Charles S. Zuker and Nicholas J. P. Ryba, Cell, Oct. 16, 2009. The authors take us on a tour of the tongue and through a series of animal experiments to demonstrate the “logic” of how tastes are coded and transmitted to the brain.

2. “Nutritional Implications of Genetic Taste Variation: The Role of PROP Sensitivity and Other Taste Phenotypes,” by Beverly J. Tepper, Annual Review of Nutrition Volume 28, 2008. This review provides a historical overview of the discovery of genetic variations in bitter taste perception and evaluates the conflicting evidence for a relationship of genetic variations in taste receptors to food choice, diet and health.

3. “Molecular Mechanism of the Sweet Taste Enhancers,” by Feng Zhang et al., Proceedings of the National Academy of Sciences, March 9, 2010. This study of a sweet enhancer demonstrates how researchers can use molecular biology and drug development to produce new compounds that can reduce the amount of sugar added to food and block the bitter taste of medicines, artificial sweeteners and vegetables.

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