GAINESVILLE, Fla. — Science is trying to build a better supermarket tomato.
At a laboratory here at the University of Florida’s Institute for Plant Innovation, researchers chop tomatoes from nearby greenhouses and plop them into glass tubes to extract flavor compounds — the essence of tomato, so to speak. These flavor compounds are identified and quantified by machine. People taste and rate the hybrid tomatoes grown in the university’s fields.
“I’m 98 percent confident we can make a tomato that tastes substantially better,” said Harry Klee, a professor of horticultural sciences. He hopes that the fruits of his labor will be available to commercial growers within four or five years and in supermarkets a couple of years after that. He thinks he can make seeds for better tomatoes available to home gardeners even sooner, within a year or two.
The insipid-tomato problem is well known both to salad lovers and scientists. For example, a gene mutation that tomato breeders love because it turns the fruit a luscious red also happens to make it blander. Refrigeration, transportation and other factors also take their toll. Over the decades, the average tomato has become not only less tasty but less nutritious.
Enter Klee, who helped found the Institute for Plant Innovation a decade ago and has been on a quest for a more flavorful and nutritious mass-market tomato ever since.
It is easy to find a better tasting and more nutritious tomato. Go to a farmer’s market or grow one in the backyard. It is also easy to breed a plant that produces something tastier than a supermarket tomato — cross a sweet heirloom with the supermarket variety. In the greenhouse, Klee pulls one such hybrid tomato off a vine, and it does taste sweeter. But a hybrid also loses some of the qualities highly valued by commercial growers — it is not as fecund, not as resistant to disease, not as easily grown, not as pretty.
As growers are paid by the pound, a better-tasting but less productive tomato holds little economic appeal, and thus was the supermarket tomato doomed to blandness.
‘Five key genes’
Klee’s goal is to tweak the tomato DNA — through traditional breeding, not genetic engineering — to add desired flavors while not compromising the traits needed for it to thrive commercially. “I figure that with approximately five key genes we could very significantly improve flavor,” he said. Three genes that control the production of key flavor compounds have already been located, he said. The next step is to identify versions of the genes that lead the tomato plant to produce more of them.
The chemistry of tomato flavor has three primary components: sugars, acids and what are known as volatile chemicals — the flavor compounds that waft into the air carrying the fruit’s aroma. There are more than 400 volatiles in a tomato, and Klee and his collaborators set out to first determine which ones are the most important in making a tasty tomato.
This involved grinding up a lot of tomatoes, looking at what was in them, and asking a lot of people to taste them (unpulverized), gathering comments like “a bland firm watermelon,” “soft and sloppy,” and “Sweet! Finally a sample with some sweetness.”
From there, Klee and his collaborators, who include Linda Bartoshuk, director of human research at the university’s Center for Smell and Taste, used statistics to correlate people’s preferences with the presence, or absence, of particular flavor compounds, to devise a chemical recipe for the ideal tomato.
The supermarket tomato — even when grown with care and picked ripe — did not excel. “The best it will do is middle-of-the-pack,” Klee said.
Cherry Roma tomatoes were at the top of the charts, followed by heirloom varieties like Matina, Alisa Craig and Bloody Butcher. Other heirlooms like Marmande and Oaxacan Pink ranked at the bottom, below the supermarket tomatoes, though perhaps these particular types just do not grow well in Florida.
The taste analysis produced several surprises. Some compounds, abundant in many tomato varieties and thus thought to be major contributors to flavor, turned out to be irrelevant, while others, in scant quantities, had major influences. With the new knowledge, “you can’t help but get a better tomato,” Bartoshuk said.
The most important attribute was sweetness. The sweeter the tomato, the higher the rating. The biggest surprise, though, was that it was not just sugar that made a tomato sweet. Some of the flavor compounds enhanced the perception of sweetness.
That is the key to Klee’s plans. Tomato breeders have already tried to maximize sugar, but the plants are bred to produce a lot of big tomatoes all at once, and then do not have energy and sunlight through photosynthesis to make enough sugar to go around.
The sweetness-enhancing compounds, however, are present in much smaller quantities, so getting a plant to produce more of those is a much more achievable goal, Klee said. (The compounds also offer promise for sweetening other foods without adding the calories of sugar.)
“His work is really groundbreaking,” said James Giovannoni, a professor of plant biology at Cornell who studies the ripening of fruit and was one of the leaders in the sequencing of the tomato genome published last year.
He said Klee has been deciphering the molecular machineries in tomatoes that produce the flavor compounds, and that is not an easy task. “One, there is a lot of them,” Giovannoni said, “and two, a lot of them are really not understood, how some of these produce these compounds hasn’t been known.”
Klee does not expect the improved tomato to taste as good as the best heirlooms. Supermarket tomatoes would still be grown in large quantities, picked green and shipped long distances before being gassed with ethylene to ripen. In addition, the tomatoes are often mishandled en route. Refrigeration, Klee notes, destroys the flavor compounds in even the best tomato. “I might be able to get 75 percent” of the best tomato in one that can be grown in greater quantities, he said.
Some traditional breeders are skeptical that Klee can do what he thinks he can as quickly as he predicts. “I don’t think the taste of tomatoes is going to be fixed by molecular biologists,” said David Francis, a professor at Ohio State University who has bred and released several tomato varieties, “because flavor is a lot more complicated than manipulating one or two genes.”
Over the decades, your average supermarket tomato — bred for looks and the ability to travel well — has become less tasty and less nutritious. Scientists hope to change all that, though, creating a tomato that tastes better while remaining viable to commercial producers.