Building a Better, Tastier Tomato

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UC Davis's Roger Chetelat holds a few "square tomatoes."

Decades ago, researchers figured out how to create the picture-perfect tomato that travels well and is available year-round. The trouble is, as any supermarket shopper can tell you, tomatoes that look great sometimes taste terrible.

It’s not hard to see how much some tomatoes have changed. Just take the trucks on California highways during the summer, each pulling a double trailer stacked high with tomatoes. There’s a reason the tomatoes at the bottom of the pile aren’t squished into a tomato-y mess. That's thanks to the square tomato.

“The square tomato is kind of a misnomer,” says Roger Chetelat, director of the Tomato Genetics Resource Center at the University of California-Davis. We’re in a greenhouse on campus where he’s holding a few square tomatoes.

“You can see they’re not square but they are blocky,” he says. The tomatoes are sort of flat on the side and are firm to the touch even though they’re ripe, sort of like a baseball. “I think I’d prefer to have a tomato like that thrown at me than a baseball, but yeah, they’re pretty tough,” Chetelat says.

Fifty years ago, farmers were looking for tougher tomatoes that could withstand new mechanical picking machines. So, plant breeders at UC Davis created a tomato with thick skin and a firm, meaty inside. California’s tomato production boomed.


Unintended Genetic Consequences

But the era of modern plant breeding came with some unintended effects, as UC Davis researcher Ann Powell discovered.

She demonstrates with a genetic taste test, of sorts. “We can try one of these,” she says, cutting up a standard grocery store tomato. “Tastes tomato-y.”

Young tomatoes with green shoulders on the left and no shoulders on the right.

The other one we’re sampling has what Powell calls “green shoulders.” That means, as it grew, the tomato was dark green on top around the stem – something that’s controlled by a specific gene.

“They’re sweeter,” Powell says, tasting it. “Whether it’s all due to that particular gene, I can’t tell you. But, I don’t know, you can taste the difference.”

If green shoulders don’t sound familiar, that’s because most commercial tomatoes don’t have them anymore. Seventy years ago, breeders selected for uniformly light green tomatoes with no shoulders, which stood out better against the plant’s dark leaves.

“They’re a lot easier to see so a farmer could judge his yield. They could see how productive the plants were a lot easier,” says Powell. Their uniform color was also more attractive to consumers.

It turns out, those green shoulders have a key job. “We found that it influences the amount of sugar in the ripe fruit,” she says. The dark green parts have more chloroplasts, which turn sunlight into sugars.

“It made about a 20 percent difference in the amount of sugars. I think of it a little bit like how you eat berries. Most of us, including me, sprinkle a little bit of sugar on top to sort of enhance the flavor,” says Powell.

Ann Powell looks at tomatoes in a UC Davis greenhouse.

Most heirloom tomatoes still have green shoulders, but Powell says now that they know about this gene, plant breeders could put it back in commercial varieties. And since the tomato genome was sequenced earlier this year, there are still other flavor genes to study.

Focusing on Taste and Nutrition

“We’ve modified and changed our food radically,” says Alyson Mitchell, professor in UC Davis’s Food Science and Technology Department.

“We’ve bred these seeds and plants to have all of these other characteristics: uniform shape, size, color, good disease resistance, high yield,” she says. That’s had major benefits: produce is widely available and more affordable.

On the other hand, “we’ve absolutely not paid attention to flavor and nutrition. You know, we’re telling children, eat more fruits and vegetables at a time that fruits and vegetables have never tasted worse,” Mitchell says.

Scientists are just starting to understand the molecular compounds that control taste and nutrition. “What we do know is that not all tomatoes are the same. Different cultivars have different levels of nutrients in them,” she says.

Growing them organically can also change the levels of nutrients. In a ten-year controlled study of tomatoes, organic tomatoes showed higher levels of antioxidants and molecules that make up flavor and color. But researchers still aren’t sure which of these compounds are the most important for our health. Take flavonoids, which have gotten a lot of hype as antioxidants.

“There are about sixteen hundred described flavonoids to date and we don’t even really at this point understand what that complement is, let alone what all of those different compounds do to benefit our health,” Mitchell says.

Even if there is one nutrient that stands out, it’s not always easy to enhance it. Take the case of “super broccoli.” “So they made this broccoli and the idea was to market it as a super broccoli because it had very high levels of this antioxidant, quercetin. Well quercetin is really bitter and they sat a bunch of people down to eat and nobody could eat it, it was so awful,” says Mitchell.

Mitchell says it’s probably the combination of nutrients that gives produce its punch, which they’re working to understand better. Until then, she says, there is one way to make sure you’re getting those benefits: follow your mom’s advice and eat more fruits and vegetables.