A jug of wine, a loaf of bread and now, vanilla.
Yeast has long been pressed into service for making food and drink, and now scientists have recruited the fungus for a loftier flavor: vanillin, vanilla’s dominant compound. Scientists report in an upcoming Applied and Environmental Microbiology that they have engineered strains of beer and baker’s yeast to produce vanillin from glucose, a greener and cheaper route than previous methods.
“This is absolutely beautiful work,” says John Rosazza, a medicinal and natural products chemist at the University of Iowa in Iowa City. There is a huge market for vanillin, Rosazza says.
Vanillin is the dominant compound of the hundreds that are found in vanilla — an extract from the seed-bearing pods, called beans, of two orchids, Vanilla planifolia and Vanilla tahitensis. But real vanilla beans are precious, rare and costly. Today, less than a percent of the vanillin sold each year is derived from the orchids. The majority of vanillin is synthesized in chemistry labs, and typically made from lignin, a constituent of wood left over from the paper-making industry, or guaiacol, which is derived from wood creosote.
Scientists have also used microorganisms in a multistep process to make vanillin from two plant compounds, ferulic acid and eugenol. But these precursors are expensive and the process involves environmentally unfriendly chemicals, says Jørgen Hansen of Evolva Biotech’s Copenhagen office. Also, vanillin itself is toxic to many microorganisms, complicating matters.
Now Hansen, Birger Lindberg Møller of the University of Copenhagen in Denmark and colleagues created a chemistry lab of their own within two different species of yeast: Schizosaccharomyces pombe, also known as fission or beer yeast, and baker’s or brewer’s yeast, Saccharomyces cerevisiae. Instead of using the typical expensive starting material, the team turned to glucose, a cheap and available sugar. To make the yeast convert the glucose to vanillin, the researchers added genes that encode for specific enzymes that spur the reactions. These genes included one from the dung mold Podospora pauciseta, two bacterial genes and a human gene.
The team also knocked out the gene that directs the conversion of vanillin to an undesirable form. The researchers report that they were pleased with the yields: the beer yeast made 65 milligrams per liter, the baker’s yeast 45 mg/l.
To further increase the yeast yield of vanillin, the researchers then added an additional gene that encodes for a plant enzyme that converts the straight vanillin into a form with a sugar attached, vanillin beta-D-glucoside. This form isn’t toxic at all, says Møller, allowing the yeast to hold much more the compound. And because the added sugar is easily broken down in the mouth or on the skin, both the straight and sugar-laden vanillin could be used in foods and perfumes.
Vanillin may also find its way into pain-relieving drugs, Møller says. Vanillin is one of the molecules in the biochemical pathway that leads to capsaicin, the compound that gives chili peppers their heat and is under investigation as a pain reliever.
“Somehow all people like vanilla,” he says. “Why? Is it the immediate taste? Does it hide some pain we’re not aware is there?”
While synthetic vanillin doesn’t offer the rich flavors of true vanilla, the artificial form has its place, says Daphna Havkin-Frenkel, director of research and development at Bakto Flavors in Rutgers, N.J.
If you seek real vanilla, though, read your labels carefully, she says. Calling synthetic vanilla real vanilla “is almost a political problem,” she says. “People are very passionate about vanilla.”