Fruit of researchers’ labor: Flavor
Tomatoes from the store have shelf life, but lack that unique taste. Now we may be closer to having both.
There’s a revolution coming to your supermarket, and it’s going to start in the tomato aisle.
After more than a decade of study, researchers at the University of Florida have identified the chemical compounds responsible for giving a great tomato its distinctive sweet, earthy, slightly grassy taste. They have also determined the genes that code for these chemicals and where they can be found in the tomato genome.
Their results, published Thursday in Science, could help breeders create tomatoes that are hardy enough to survive the often long and arduous journey from field to store without sacrificing flavor.
Experts say we could be on the brink of a tomato game-changer.
“Now that all of us in the community know the genes that are relevant for emphasizing flavor, there is no reason we shouldn’t be able to make great tomatoes,” said Ann Powell, a recently retired tomato researcher at UC Davis who was not involved in the work.
Nobody set out to create a tasteless tomato, of course. Instead, scientists say, modern commercial tomatoes were consistently bred for other traits, including shelf life, firmness and disease resistance.
“That’s all very important, but as they bred for these things, modern tomatoes lost their flavor,” said Denise Tieman, a research assistant professor at the University of Florida and the first author on the paper.
Harry Klee, a professor in the horticulture department at the University of Florida who led the work, added that the taste probably deteriorated so slowly that most growers didn’t notice the change.
“It was certainly not intentional,” he said. “It was just a slow, imperceptible degradation of flavor.”
Determined to right this wrong through science, Klee has been studying the chemical origins of tomato flavor for 25 years. His lab’s earlier work showed that although sugars and acids make up the bedrock of the classic tomato taste, it is trace amounts of naturally occurring chemicals called aroma compounds that make a truly delicious tomato sing.
“The real excitement of food is what you smell,” Tieman said. “When you chew, these aroma compounds get into your olfactory systems, and that’s what really makes things taste good.”
In the new study, Tieman, Klee and their collaborators analyzed 398 types of tomatoes — including modern, heirloom and wild species — to determine both the biochemistry and the genetics of great tomato flavor.
It was a tremendous amount of work.
All the tomatoes in the study were grown by the research team in greenhouses and in the field. About 100 of the varietals were given to 70 to 100 taste testers who rated them on intensity of flavor, sweetness and other attributes.
Next the group analyzed the chemicals in each tomato to determine what mix of sugar, acids and aroma compounds seemed to get the highest marks from the taste testers. They identified about 60 chemicals that appear to play a significant role in tomato flavor.
In the meantime, the team’s collaborators in China sequenced the complete genomes of the nearly 400 tomato varieties included in the research. The results allowed them to determine the genes that code for the flavor-enhancing aroma compounds necessary for good tomato flavor.
Powell, the retired tomato expert from UC Davis, said the new work is exciting because it gives breeders a genetic road map for putting flavor back in the fruit.
“Tomatoes are used in cuisines around the world, and different cultures have different preferences for flavors they like,” she said. “In Japan they like them super sweet, and in parts of Europe they like them with that green taste. Thanks to this work, the tomato can be made much more versatile.”
Klee’s group has already started to breed a few tomatoes that they hope will appeal to growers who value shelf life, disease resistance, high yield and hardiness as well as to consumers who value taste above all.
Lab members are making their new cultivars the old-fashioned way, by collecting pollen from one flower and manually putting it on a flower from a different plant.
Klee notes that genetics are not the only factor that affects how good (or bad) a tomato tastes. For example, tomatoes picked when they are green will usually have less flavor than those picked when they are fully ripe. Also, his lab’s previous work has shown that tomatoes stop creating those allimportant aroma compounds when they are chilled.
Finally, the environment a tomato is grown in can also affect how it tastes. Just as a pinot noir grape grown in Santa Barbara will taste different from one grown in Sonoma, location also plays a role in developing a tomato flavor, he said.
“That’s what makes breeding for flavor so difficult and why we want to reduce it to a set of genetic markers,” Klee said.
“We want to give tomato breeders tools for reliably selecting for the best genetics, regardless of where or how they are growing them.”
It is also possible that a similar technique could be used to return flavor to other commercial fruits that seem to have lost their way.
Supermarket strawberries, for example, seem ripe for a flavor upgrade.
“The strawberry breeder can’t use the same genes we are using, but what they can do is apply the same approaches,” Klee said, adding that some of his former students have been hired by a big commercial strawberry breeder to do just that.
The revolution has begun.