Harry Klee, molecular horticulturalist

Would people eat more fruits and vegetables if they tasted better? This tomato connoisseur believes so. Interview by Paul Gabrielsen

April 02, 2013


Harry Klee is tinkering with the chemical balances within tomatoes to make them tastier. University of Florida/IFAS photo by Tyler Jones

There’s nothing quite like the taste of a fresh, homegrown tomato — as juicy, rich, and sweet as supermarket tomatoes are pale, cold, and bland. Starting shortly after World War II, high demand for year-round produce led tomato breeders to select for appearance and hardiness, not flavor. The result, for fruits and vegetables all over the produce section, is a tasteless product that justifiably earns the scorn of kids everywhere.

Molecular biologist and horticulturalist Harry Klee of the University of Florida (UF, home of the Gators), is determined to redeem the lowly tomato. Better-tasting vegetables inspire better diet choices, he says. By tweaking the fruit’s intricate chemical recipe, Klee hopes to bring back the bygone flavors of yesterday’s tomatoes.

Using chemistry, genetics, and taste tests, a team including Klee and UF psychologist Linda Bartoshuk identified the volatile chemicals that contribute most to better-tasting tomatoes. “Volatile,” in this case, refers to chemicals that evaporate easily, which emanate from our food as we chew and swallow. The results surprised Klee, because the list didn’t match a previous assessment of tomato flavor chemistry based on “sniff tests,” not taste tests. The science of flavor, he’s learned, is full of surprises.

Now he’s tapping the genetic diversity of heirloom tomato breeds to maximize the right volatiles and develop the perfect blend of tomato taste and durability. He’d prefer to genetically engineer an ideal tomato; in fact, he’s already done so in his lab. But commercializing a genetically modified organism can cost up to $15 million in the United States, so he’s sticking with a traditional cross-breeding approach. “It adds years to the time it takes us to get a product, but we have no choice,” he says.

Klee described his quest during a symposium titled “Fixing the Broken Tomato: What We Like and Why We Like It” at the February 2013 meeting of the American Association for the Advancement of Science in Boston. SciCom’s Paul Gabrielsen joined Klee afterward to squeeze out the juicy details.

Why does the world need better-tasting tomatoes?

The number-one problem we face today is obesity. People are not eating healthy diets, and part of that is choice. If we can make foods that taste better, people will make more intelligent decisions about their diets. The stuff you buy in the supermarket does not meet the expectations of the consumer. As a consequence, they don’t buy it. So, instead of eating what’s really good for you, you eat what tastes good.

"I don’t buy into the 'local' philosophy: eating only what’s in season locally. People want to go to the store and buy a tomato when they want a tomato."

Can you describe what the ideal tomato tastes like?

Well, ideally the texture is going to be good — not too hard, not too soft. It’s going to have sweetness and some acid that balances that sweetness. Then you’re going to get that burst of flavor. The volatile chemicals that we work on should really almost explode in your mouth with flavor.

If you mix these volatile chemicals together in a test tube and taste them, will that be a tomato?

No, because flavor is so incredibly complicated. Flavor involves almost all of our senses. If you see a typical supermarket tomato, they’re kind of a pale red, giving the impression that the tomato is not fully ripe. That is going to physically influence how you taste that tomato and what you think of its taste.

It starts with vision, and with texture in your mouth. What does it feel like as I chew on it? How are the chemicals in the fruit released as I chew on it? Then the taste — the receptors on your tongue pick up sugars and the acids, and then the volatiles, when you swallow. So, I can mix a bunch of volatile chemicals, and I can stick them under your nose and say, “Does that smell like a tomato?” You’ll answer yes. But if you put it in your mouth, it would have no resemblance at all to a tomato.

You previously had a list of chemicals thought to influence tomato flavor, but now that list has been overturned. What do you think of that result?

As a horticulturalist I was a little surprised, but as soon as I started talking to psychologists, they said, "Of course!" Who would’ve been stupid enough to think that in the first place? As Linda Bartoshuk says, when you smell a chemical through your nose, versus when you chew on it and it goes through the back of your mouth, your brain knows the difference. Nobody knows how that works. The same chemicals are perceived differently by your brain.

We have five (or four, depending on whom you talk to) classes of taste receptors, and we have about 350 volatile receptors, all of them different. That’s where the complexity comes from.

How did you and Linda begin collaborating on tomatoes?

The head of our college got us together in a room. He said, “You know, I think both of you have things in common, and you should talk.” We were looking at very similar problems from exactly the opposite directions. I said, “You can measure quantitatively how much people like something, and how chemicals might interact to give you an impression of a flavor?” She said, “Of course, that’s what we do.”

And then I would say, “We’ve got all these different tomatoes that are hugely different chemically, and we can give them to people.” She says, “Really? You’ve got this incredible diversity in a product that we can test, and look at people’s preferences?” And I said, “Well, yeah, of course.”

Suddenly we realized that we were on the same campus and could help each other take science to another level. That, to me, is the fun part of science. When you take people with really different expertises and backgrounds and put them together, really cool stuff can happen.

You’ve found that some volatiles enhance sweetness without increasing sugar. What are the implications of your discovery?

It gives us real hope that we can make the tomato taste better for consumers, because we know that sweetness is the major driver of liking. Where we may have a real potential impact is in processed foods. If we can achieve the same sweetness by replacing sugar with these volatile chemicals, we could reduce the caloric intake of the diet tremendously. People want those products. But can we potentially take some of the sugar out and make it taste just as desirable? I’m very optimistic the answer is yes.

How would these volatile sweeteners differ from current artificial sweeteners?

Well, they’re natural products. They already exist, and we’re just providing the code for which ones work. They’re products we ingest every day, and all we’re doing is maybe upping the levels of them. A lot of the artificial sweeteners work in a totally different way, because all of them bind to taste receptors, and a lot of them are associated with bitter off-tastes. They have some significant downsides.

In your experiments to create the perfect tomato, have you bred any that taste worse?

Oh, yeah! You’ve got to get the levels right, even with sugar. There’s an optimum level for how much sugar adults like, and if you go too far people like it less. That level, the optimum, is exactly the sugar content of Coca-Cola. The same goes for volatiles. There is an optimal level; if you put too much in, it’ll give it an off flavor.

For most of the chemicals, we need more but not way more: 50 percent more, or double at most, which is achievable. There are a few of the chemicals where you actually want less. A few chemicals in tomato give it off flavors, like a mediciny taste in high doses. We’ve determined the optimum level for each of those chemicals.

What’s your favorite tomato product?

I’ve eaten so many fresh tomatoes to try and find good ones that I’m actually pretty sick of fresh tomatoes. I eat a large amount of processed tomatoes, pasta sauces, those kinds of things. I bring home a lot of the tomatoes from the field and generally make sauce or paste out of them, but I’m pretty burned out on raw tomatoes.

What’s the answer to the problem of a year-round demand for fresh vegetables?

I don’t buy into the “local” philosophy: eating only what’s in season locally. That’s too restrictive. People want to go to the store and buy a tomato when they want a tomato. The problem with trying to fill that need is the industrial tomato, for lack of a better term. That’s a reality. We have to get that tomato from Mexico or from Florida, and we have to do it fairly cheaply.

Knowing what we know now about the genetics of flavor, we can actually improve the quality of that bulk commercial tomato. It’s never going to taste as good as an heirloom tomato, grown in your backyard, picked when it’s fully ripe, and taken right indoors. That’s not going to happen. But we can make it taste a whole lot better than it does right now.

How did you end up as a tomato scientist?

My undergraduate degree is in psychology. I got interested in drugs and chemistry and how the brain works, so I got a Ph.D. in biochemistry. That eventually merged into plants.

I work on tomatoes because they’re really an interesting model for a geneticist and a molecular biologist. We were working on ethylene, which causes the fruit to ripen, for a number of years before we really got directly into flavor. It was a natural transition.

I was naïve enough, 10 or 12 years ago, to think we could understand flavor. It turns out it’s a really hard problem, a really complex thing. I can count on one hand the number of people in the world who are working on this, because it’s such a hard problem. It’s taken a lot of hard work and integrating a lot of different people’s expertises to fix it. I think we’ve made great progress.

Once you’ve fixed the tomato, what’s your next target?

My collaborators are already working on strawberries and blueberries, using the same techniques and the same methods of figuring out the best composition and working on the genetics. I think what we learn from the tomato is applicable to other crops. I would be happy if we could just [improve] tomatoes to the point where people really are much happier with them.

Do you already have a name picked out for your perfect tomato breed?

No, but it’s probably got to involve Gators.


Paul Gabrielsen, a graduate student in the Science Communication Program at UC Santa Cruz, earned his bachelor's degree in geology from Brigham Young University and his master's degree in hydrology from New Mexico Tech. At UCSC, he has worked as a reporting intern at the Santa Cruz Sentinel, Stanford University News Service, and ScienceNOW, the daily website of Science magazine. This summer, he will intern in science outreach at the NASA Goddard Space Flight Center in Greenbelt, Maryland.

© 2013 Paul Gabrielsen