Harvard Medicine

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A Pinch of Salt

The secret to this magical ingredient remains elusive to scientists.

© pixhook<br/>iStockphoto.com Modern chemists know better than to wave a pipette or gloved finger near their mouths. But in 1879, curiosity trumped safety—and produced a sweet surprise.

Johns Hopkins chemists Constantin Fahlberg and Ira Remsen discovered saccharin in an accidental tasting. The reports vary, but only in the details—in one account, Remsen transferred the compound from laboratory equipment to hand to dinner roll to mouth; according to another account, Fahlberg’s taste traveled from pencil tip to tongue. The serendipitous discovery led to four patents.

But how, exactly, did these chemists detect that sweet taste physiologically? None of the cellular receptors involved in triggering the brain to detect a sweet sensation on the tongue were known until this century. In fact, none of the cellular receptors for sweet taste were identified until researchers—including a team led by Linda Buck, then an HMS professor—discovered them in 2001.

Today, scientists have identified receptor genes for four of the five tastes: bitter, sweet, sour, and umami, or savoriness. The cells that make up our taste buds express these genes to create receptors that detect the molecular tastants and trigger a signal to the brain.

What remains to be understood is the one flavor used to heighten the taste of everything, from cookies to grilled steak to butter: salt. “Candidate salty receptors have been proposed, but it isn’t clear that these are in fact the key mediators of salt taste,” says Stephen Liberles, an HMS assistant professor of cell biology who worked with Buck on the taste receptor studies. Liberles’s interest in the function of such receptors stems from his ongoing investigation into how sensory cues govern our behavior.

Understanding these various taste receptors—the channels leading to our enjoyment of flavorful foods and our rejection of vile ones—could help researchers develop safer tools than their own tongues for taste-testing new compounds.

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