U. FLORIDA (US) — Without the enzyme CXE1, tomatoes might not be so tasty, a new study finds.
Chemical reactions triggered by CXE1 improve the fruit’s flavor profile by reducing the presence of acetate esters, volatile chemicals commonly associated with plant defense and plant-to-plant communication.
“We do believe this phenomenon makes the fruit more palatable,” says Harry Klee, molecular biologist in the horticultural sciences department at the University of Florida.
Previous tomato research has shown that consumers don’t like the contributions that acetate esters make to tomato flavor. While they may be pleasant in isolation—for example, butyl acetate has a sweet, banana-like odor—they don’t match consumers’ ideas of good tomato taste, he says.
Klee and his colleagues are involved in a long-term effort to uncover genes and biochemical pathways responsible for producing the volatile chemicals that give fresh tomatoes their characteristic flavor and aroma.
Ultimately, they hope to show that great taste is dependent on just a handful of compounds in the right proportions. Breeders can then use the information to guide their efforts to develop improved varieties.
CXE1 and four similar enzymes appear to play a role in establishing the acetate ester content of tomato fruit. To better understand the enzyme’s role in tomato flavor, the researchers investigated what would happen without it.
They engineered tomato plants that produced very little of the enzyme. Fruit from those plants contained higher-than-normal levels of acetate esters.
The team also analyzed Solanum pennellii and Solanum habrochaites, relatives of the tomato plant that produce green-skinned fruits unpalatable to people and seldom eaten by animals. The fruits contained large amounts of acetate esters, compared with tomato fruit. Further analysis showed that those plants produced little CXE1.
In laboratory tests, CXE1 inhibited the activity of numerous acetate esters, though the enzyme was more active against some than others. Findings are published in the Proceedings of the National Academy of Sciences.
It’s possible that high CXE1 production in tomato plants is a trait that evolved in tandem with red-skinned fruit, providing a survival advantage. Perhaps the red color drew attention from animals and the pleasant taste inspired them to eat the fruit, leading to seed dispersal that established the plant in new areas.
Though this study may shed light on the tomato’s distant past, Klee is much more interested in its future.
“Because acetate esters are negatively correlated with consumer liking, we want to find ways to get rid of them,” he says. “I always tell people there are probably five or 10 chemicals we need to optimize to achieve an ideal flavor balance in tomato, and I think CXE1 is probably part of that group.”
Source: University of Florida