The Scientific Search for the Essence of a Tasty Tomato

Image: torbakhopper/Flickr

Scientists are several steps closer to restoring flavor to the supermarket tomato, a once-magnificent fruit turned by commercial pressures into a juicy orb of gustatory cardboard.

After 13 consumer tasting panels evaluated samples of 158 heirloom tomato varieties, researchers statistically correlated their responses with molecular analyses of tomato composition. From this emerged a profile of some two dozen chemical compounds that made the fruits taste good.

Such a profile has long eluded researchers, for whom the tomato represents a challenge of surprising complexity.

“With something like a banana, you can identify one volatile compound that you smell and say, ‘Aha! It’s a banana!’ With a tomato, it’s not that simple,” said plant molecular biologist Harry Klee of the University of Florida. “You can detect 400 volatile compounds in a tomato. People have speculated that maybe 20 are really important, and they need to be orchestrated properly. It’s a little more complicated than we like.”

Klee and colleagues’ latest study, “The Chemical Interactions Underlying Tomato Flavor Preferences,” was published May 24 in Current Biology and represents the latest stage in a decade-long effort to identify the genetic and molecular underpinnings of tomato taste.

The project, which has involved psychologists, statisticians, molecular biologists and various food scientists, is described in Barry Estabrook’s 2011 Tomatoland, which also chronicles the fruit’s historical journey from South America to Spain and back to the New World, where it’s recently been transformed into a studio prop of itself: big, red and mostly tasteless.

Fueling that devolution was a consumer desire for year-round fresh fruit and the tradeoff of high yields, disease tolerance, aesthetic value and shelf life for flavor, which until recently was a low priority for commercial breeders. Klee hopes to change that.

“Growers are not paid for producing a better-tasting tomato. Growers are paid for producing a large quantity of red objects,” Klee said. “I always get asked, ‘Are we raising a generation of people who don’t know how a tomato should taste?’ And I think the answer is largely yes.”

After presenting heirloom tomatoes — non-commercial plants, with names like Oaxacan Pink and Crimson Sprinter, Giant Oxheart and Skorspelka Red — and supermarket varieties to tasters, Klee’s group cross-referenced their evaluations with chemical analyses of each tomato. Statistical distillation produced a list of compounds numerically correlated with positive taste.

Analyses of tomato varieties (y-axis) according to 70 chemical attributes (x-axis). Image: Tieman et al./Current Biology

The researchers then used genetic engineering to design tomatoes in which individual compounds were removed or enhanced, allowing precise tests of how each chemical affected flavor. Similar tests were conducted with heirloom varieties known to be near-identical except for the presence or absence of key compounds.

From all this emerged an even clearer picture of tomato chemistry. A class of chemicals called C6 volatiles, which are abundant in tomatoes and thought crucial to their flavor, proved irrelevant to consumer taste. Another 27 compounds were flagged as important, including a little-appreciated trio — arcanely known as geranial, 2-methylbutanal and 3-methyl-1-butanol — that shaped sensations of sweetness.

For the moment, these chemical traits can’t be linked to genetics. The tomato genome is understood only at a coarse level of detail, and plants that appear genetically similar can produce fruits with wildly different chemical characteristics. Future research should establish genetic links, said Klee, and allow agricultural companies to breed supermarket-suitable tomatoes that combine commercial viability with greater taste.

“We’re working with the big seed companies to get them to understand the genetics and flavor and breed it back in,” said Klee. “Putting the flavor back into something that still retains all that yield, shape and disease resistance is a big task.”

In the meantime, Klee is freely sharing the seeds of his group’s own in-house varieties with home-garden growers. “We’ve taken some of the heirlooms and crossed them with some of the more modern, highly disease-resistant varieties,” he said. “We’re testing them in the field now. Tomorrow is our first harvest. They taste great.”

Image: Torbakhopper/Flickr

Citation: “The Chemical Interactions Underlying Tomato Flavor Preferences.” By Denise Tieman, Peter Bliss, Lauren M. McIntyre, Adilia Blandon-Ubeda, Dawn Bies, Asli Z. Odabasi, Gustavo R. Rodrıguez, Esther van der Knaap, Mark G. Taylor, Charles Goulet, Melissa H. Mageroy, Derek J. Snyder, Thomas Colquhoun, Howard Moskowitz, David G. Clark, Charles Sims, Linda Bartoshuk, and Harry J. Klee. Current Biology, Vol. 22 No. 11, 25 May 2012.