Discovering the Sweet in Basil

Only recently have scientists worked out what makes sweet basil an aromatic and minty-tasting herb

Sweet basil
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As autumn brings an end to summer herbs, food processors around the country are whirring up batches of one of fall’s most-anticipated culinary indulgences—sweet basil pesto. The ingredient at the heart of the thick, green manna—Ocimum basilicum—has been prized for millennia for being both sacred and royal.

But only recently have scientists worked out the details of the chemical pathway that makes sweet basil an aromatic and almost minty-tasting herb instead of, well, a stick.

A research team led by Joe Noel at the Salk Institute for Biological Studies in La Jolla, Calif., used x-ray crystallography to take a 3-D picture of the plant enzyme eugenol synthase in mid-reaction in the lab. With the structure of the fleeting molecule in hand, the team filled in a missing step in how the plant manufactures its rapturous properties.

According to Noel, most of the enzyme’s cousins carry out mundane house keeping tasks in plant cells. But basil eugenol synthatase, or EGS, acquired a completely new function through evolutionary selection.

"Eugenol synthase takes a basic building block that is usually employed to make wood and turns it into something that is almost the complete opposite—a volatile molecule that easily becomes airborne, is highly aromatic and possesses antimicrobial and pain-dulling properties," said Noel.

Plant biology has been undergoing a sort of renaissance, Noel said, because the natural food movement sparked newfound interest in the health-promoting and medicinal properties of natural plant chemicals.

"We are consuming all these chemicals as part of our diet, some of which are very beneficial, preserve our food and impart some really interesting flavors and fragrances for our taste buds and noses, but some of which are toxic," he said.

Plants rely on a complex set of bioactive volatile chemicals, which diffuse easily through the membranes of cells that produce them to communicate and interact with the outside world. These often aromatic and highly specialized compounds entice pollinators, fend off pathogens, bacteria, and leaf-munching animals.

Understanding the biosynthetic pathways used by plants to make these compounds may help scientists improve the flavor and nutritional quality of plants that are part of our diet. Being able to tinker with natural scents could resurrect the waning scent of roses or create novel fragrances for the perfume industry.

But scent engineering has the potential to do more than please human noses. It could increase crop yields by enticing new pollinators or natural pest controllers such as parasitic wasps to visit commercially grown plants.

The study, which was published in the Oct. 4, issue of the journal PLoS ONE, was supported by the National Science Foundation.

—Leslie Fink, NSF

This report is provided by the National Science Foundation, an independent federal agency that supports fundamental research and education across all fields of science and engineering, in partnership with U.S. News and World Report.