"Tomato flavor is the result of a combination of sugars, acids and volatile compounds. Volatiles are the aroma compounds that give tomato its unique flavor. Without these aroma compounds, the tomato would not taste like a tomato. There are many volatiles that contribute to tomato flavor, and each must be in the right concentration to yield good tomato flavor. This is why it has been difficult to breed for flavor in tomato", explains Denise Tieman, research assistant professor with the University of Florida, who has spent years researching the impact of volatiles on tomato flavor.
Esther van der Knaap of the University of Georgia, who has worked with Harry Klee and Denise Tieman to research tomato flavor, adds: "The taste of tomato is incredibly complex. It consists of three components. The physical, when you bite into it, how it feels. Soft, firm, or in between. Then it's these sugars and the acids, which are very easy to evaluate. But the major component, which often people forget, is the volatiles. And volatiles are complex, but some volatile pathways are very robust. A certain volatile may be fairly independent of environment."
She adds, "If you know which volatiles are liked by people and which volatiles are not, now we can actually identify individual pathways and we know which volatiles we should temper down on and which ones we could enhance."
A way to find out consumer preferences when it comes to tomato flavor, is by organizing taste panels. That's what Harry Klee and Denise Tieman have been doing as part of their research. Denise explains how such taste panels work in practice: "We asked 60-100 people to taste the tomatoes, typically 6 varieties in one panel. The panelists were presented with 2 slices of each variety. They rated the tomatoes on overall liking, texture liking, sweet, sour, bitter, salty and umami intensity."
It was found that people who have tasted a home grown heirloom variety have very different taste expectations than someone who has only tasted a commercial tomato. The flavor complexity of heirloom tomatoes is what is desired by the first group, while the second group does not eat many tomatoes or just looks for sweet tasting tomatoes.
Back in time
On the heirloom side of the taste spectrum, the scientists from Georgia and Florida are going more into using ancestral tomatoes from South America, to identify useful alleles.
"One of our hypotheses was, of why we should look back in this semi-domesticated germplasm, maybe 5,000 years ago people were selecting for different qualities", Esther explains. "There is a region in Peru, San Martín, where the levels of alkaloids in the tomatoes are higher, and alkaloids are actually not always good. If you eat too much of them, then they're poisonous, but at low levels they actually give a bitter taste, and it may have been liked, or it may have been used for medicinal purposes. It's possible that they selected against the sweet or a certain volatile, because that was also not preferred at that time. This is why we think going back into more ancestral germplasm may help to get quality traits that were not used or left behind, and because volatiles as a whole and taste as a whole is complex, but if you can dissect it into different pathways, it's not that complicated to follow a pathway and go back in a germplasm."
That research should ultimately result in the development of better-tasting tomatoes. "We are now developing new varieties that have the attributes for good flavor, as well as the commercial traits necessary for large scale production", Denise says. "Breeders are using this technology to introduce the flavor genes into their elite germplasm."
Flavor is impacted by environmental conditions. These cannot be controlled, but starting with a good tasting variety will help. "That is, a variety with good flavor will develop the best flavor possible in poor conditions, and will taste great under the best environmental conditions. I hope the tools we have developed will accelerate breeding for improved flavor in tomato", Denise concludes.