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 J. 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 Dr. Klee, who helped found the Institute for Plant Innovation a decade ago and has been in 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, Dr. 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.
Dr. 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. He said three genes that control the production of key flavor compounds have already been located.
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 Dr. 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, Dr. 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,” Dr. 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,” Dr. 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 Dr. 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, Dr. 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 Dr. 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,” Dr. Giovannoni said, “and two, a lot of them are really not understood, how some of these produce these compounds hasn’t been known.”
Modern genetic engineering has provided tools to study that, and tomatoes are one of the most common plants that plant geneticists study, much in the same way that animal geneticists focus on mice, and now researchers can knock out particular compounds and see if they played a key role in flavor or not.
There has been one genetically engineered tomato in the supermarket. In the 1980s, plant geneticists at the University of California, Davis, just as frustrated by bland tasting tomatoes, also tried to make a better tomato. That led to a biotechnology company, Calgene, in 1994, developing the Flavr Savr tomato, the first genetically engineered food of any kind in the supermarket, its DNA tweaked to inhibit a protein that turns a tomato mushy over time. While it sold well, Calgene foundered in the logistics of industrial agriculture and was bought by Monsanto, which discontinued selling the seeds.
The Florida team is not repeating the Flavr Savr game plan.
Although Dr. Klee experiments with genetically engineered tomatoes to test and confirm findings, he said that none of the ones eventually destined for supermarkets will be — partly to avoid potential consumer backlash and partly because his university cannot afford the estimated $1.5 million that would be needed to obtain regulatory approval to sell a genetically engineered tomato.
Instead, the tomato would be created through traditional breeding techniques, but using genetic tests to determine which of the plants possess the desired genes.
The quest for year-round produce at the supermarket has also led to tomatoes being grown in less-than-ideal places — like Florida, where the soil is too sandy and there are plenty of pests — when the traditional tomato-growing areas farther north are too chilly.
Dr. 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, Dr. 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 Dr. 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 The Ohio State University who has bred and released several tomato varieties, “because flavor is a lot more complicated than manipulating one or two genes.”
After working with tomatoes for so long, Dr. Klee admits he does not eat many of them, but he does want the public to be able to buy appetizing ones. Part of his quest is to get people to eat less junk food. If he can improve the taste of tomatoes, he said, it could be an important way to coax Americans to eat healthier foods.
Tomatoes aren’t the only focus of the Institute for Plant Innovation. Researchers are working on a more fragrant rose, a project that involves the genetic engineering feat of inserting — yes — a tomato gene in a rose plant. They are also trying to grow tastier strawberries and blueberries. One new blueberry variety could be described as positively crispy, almost apple-like in its texture.
Consumers who tasted these blueberries liked their firmness, and the quality is also a boon to growers, because the fruit lasts longer.
“It’s a blueprint,” Dr. Klee said of his tomato quest, “for a much bigger program of bringing back flavor.”