There’s a certain magic in Thai food. The fire hits hard, then fades. The taste buds beg for more. This enchanting cycle of fleeting and repeating self-torture and sweet relief continues, until—the bowl of Tom Yum soup nearly drained, the last grains of rice all but devoured—you take your final peppery, lemongrassy bite.
The ancients who crafted these exotic herbal concoctions were culinary alchemists, pairing their seasonings to agonize—and to entice. Little did they know that, centuries later, scientists would be working to tease apart the secrets of their spicy mastery.
Chemicals called tastants cause the burning sensation and subsequent cooling relief so common in Asian cooking. Capsaicin, a chemical in peppers, triggers sensations of heat and pain by stimulating taste receptors on the tongue. Citral, a chemical in lemongrass, squelches that heat.
As fans of hot, spicy food may know, a sip of water amplifies the peppery burn by welding the capsaicin to the taste receptors. Milk dampens the burn as its fatty lipids flush away the compound.
“Citral makes it not so hot, but in a different way,” says Stephanie Stotz, a research fellow in cardiology at Children’s Hospital Boston. Stotz has found that citral blocks G protein-coupled receptors—transient receptor potential ion channels in taste buds—only after they have been activated and depolarized by, say, a tastant such as capsaicin. Stotz has shown that citral obstructs these open taste detectors in model cells.
But the way citral works has a temporal component: It allows a quick surge of taste response—the burn—then soothes it for an extended time—the cooling relief.
The molecular mechanisms governing the cooling effect of citral-like compounds remain a mystery. Yet unraveling these mechanisms could help lead to new pain medicines, says Stotz. “We’re eating these compounds for a reason,” she adds. “They’re helping us dampen pain and heighten pleasure.”