Most retail tomatoes are bland at best, and a single gene mutation helps to explain why.
The mutation occurred when breeders bred tomatoes to ripen uniformly, a quality that makes harvesting more cost-effective and efficient. Despite their attractive appearance, mutant tomato fruits are less effective at photosynthesizing, according to a recent research. As a result, they make less sugar and other compounds, which means they often taste far worse than tomatoes that may look blotchy but are full of explode-in-your-mouth sweetness.
For customers who want their Caprese salads rich and complex, the findings indicate that heritage varieties available at co-ops and farmer’s markets may be your best choice for the time being. Ultimately, the discoveries might assist breeders in reintroducing more pleasing taste characteristics into common grocery store tomatoes.
“When you have fruit or berries and you sprinkle sugar on top to accentuate the flavors, you can see how every little bit helps,” said Ann Powell, a biochemist at the University of California, Davis. Because of our sensitivity to sweetness, a gene for sugar synthesis is critical. “Now that breeders know which gene it is, they may select for variants while plants are young.”
For some 70 years, tomato breeders have worked to create fruits that are uniformly light green before they ripen. The benefit of this equal coloration is that fruits ripen all at once, rather than at the top end first. Farmers can now detect when it’s time to harvest considerably more easily.
Powell went on a search for proteins within the fruit called transcription factors, which control the genes that code for diverse features. He was motivated more by the subject of why tomatoes bother being green in the first place than by the question of why tomatoes so frequently taste horrible.
Her investigation led her to GLK, a kind of protein found in tomatoes. When intact, she and colleagues reported Thursday in the journal Science, the protein makes pre-ripened fruits appear dark green at the shoulder, where flesh meets stem. Fruits with the mutation, on the other hand, are bright green all throughout before becoming red.
For a long time, scientists have known that two GLK proteins in tomato and other plant leaves drive the creation of chloroplasts, which are responsible for photosynthesis, converting sunlight into sugars, and part of those sugars pass into the fruit to give sweetness.
It now seems that the fruits of tomato plants also contain a GLK protein, which increases sugar synthesis just enough to create a noticeable change in taste. The dark green shoulder indicates that increased photosynthesis is taking place. Chemical tests revealed that tomatoes with normal GLK proteins had more lycopene, an antioxidant responsible for the red color of tomatoes.
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As tomatoes become red, it’s hard to discern which ones contain the mutation, making it exceedingly unlikely that a grocery customer could identify tomatoes with naturally higher sugar levels.
In fact, the chances of unmutated tomatoes showing up in any major grocery store are extremely slim. Powell and colleagues examined 25 commercial tomato cultivars from across the globe and discovered the same mutation in all of them.
“The mutation they describe in their paper is in literally 100 percent of modern breeds sold in grocery stores today,” said Harry Klee, a molecular geneticist at the University of Florida, Gainesville, who studies the chemistry and genetics of flavor in fruits and vegetables. “It’s a pretty nice example of some of the issues with current tomato breeding.”
Klee stated that the GLK mutation isn’t the sole reason why supermarket tomatoes are typically bland. But it’s an important reason, and it demonstrates how focusing on aesthetics can end up sacrificing other important qualities in an entire generation of produce.
“When you focus on one thing and neglect the other — the other being flavor — you can have some really bad unintended consequences,” Klee said. “The customer will have to accept that their tomatoes may not be flawless. A patch of green may appear around the top of the fruit. Yet, if I see that a fruit is not completely red and evenly matured, I believe it will taste better.”