Scientists explain why tomatoes could be sweeter

Tomatoes at the Rutgers Agricultural Research and Extension Center, in Bridgeton, N.J. Those that have uniform color are found to not taste as sweet.
Tomatoes at the Rutgers Agricultural Research and Extension Center, in Bridgeton, N.J. Those that have uniform color are found to not taste as sweet. (LUIS FERNANDO RODRIGUEZ / Staff Photographer)
Posted: June 30, 2012

With tomato season nearly upon us, many a consumer soon will be scanning the shelves for specimens with that uniform hue of eye-catching red - a characteristic that shoppers have come to expect from modern agriculture.

But in the quest for good looks, they likely are giving up something in the taste and nutrition department, according to new research published Friday in the journal Science.

Tomatoes that have been bred to ripen with a uniform color contain up to 20 percent less sugar than their counterparts with green or yellow patches on the "shoulder" of the fruit, the researchers found after a genetic analysis. These uniform varieties suffer a similar reduction in the antioxidant lycopene and of beta carotene, a precursor of vitamin A.

This unfortunate trade-off is not the primary culprit in the blah taste of many supermarket tomatoes, said the authors, who hail from the University of California-Davis, Cornell University, and Spain. More important is the fact that tomatoes are commonly picked before ripening, while still green.

Still, scientists in the storied tomato research halls of Rutgers University, who were not involved in the new research, already were anticipating that the findings could guide their breeding work.

"This may become a part of what we do," said Rutgers professor of plant biology and pathology Thomas Orton.

Orton's predecessors developed the world-famous Rutgers tomato in 1934, back before New Jersey ceded its tomato dominance to California and Florida.

Yet it is still called the Garden State, after all, so Orton and his colleagues are still at the game, trying for that tricky balance between taste and the ability to withstand machine-harvesting and other demands of industrial-scale farming.

On Thursday, Orton showed off rows of tomatoes that were a uniform shade of light green, at the Rutgers Agricultural Research and Extension Center in Bridgeton, N.J. By the time they ripen, in a week or so, they will be solid, unblemished red - the very trait that, according to the new research, is tied to lower levels of sugar.

The reason good color is linked with less sugar and nutrients is that these light-green fruits contain fewer and lower-quality chloroplasts - the biological machinery responsible for photosynthesis and, ultimately, sugar production, said Cornell's James Giovannoni, one of the new paper's authors.

Photosynthesis is primarily carried out by chloroplasts in the leaves of the plant. But the research showed that photosynthesis in the fruit is significant, said lead author Ann L.T. Powell, a U.C.-Davis biochemist.

In tomatoes that lack the genetic variant for uniform color, the unripe fruit tends to be light green on the bottom and dark green on top, signifying a richer concentration of chloroplasts. When ripe, the nonuniform tomato typically retains green or yellowish markings on the crown.

One solution to the taste-for-appearance trade-off: breed tomatoes that start out entirely dark green, then retain a uniform color when they turn red, Powell said. The research team already created such a tomato in the lab.

Jack Rabin, another Rutgers tomato expert, cautions that much more than sugar is at stake in the flavor picture. Aroma is important, as is acidity. Many Easterners, he said, like a balance between high sugar and high acidity, whereas West Coasters tend to be focused purely on sugar.

Rabin is associate director of farm programs for the Rutgers New Jersey Agricultural Experiment Station, but he sometimes feels like a psychologist.

He's the one who fields calls from anguished consumers looking to relive lost youth, those days when Dad pulled over in the station wagon to buy them a luscious globe of red fruit from a roadside stand, Rabin said.

"It's dripping down your chin," he said. "You just have these warm memories of which the tomato is a part. They want that tomato back!"

Rabin loves the juicy red fruit as much as anyone, but he ended his discourse with a dose of be-careful-what-you-wish-for. Decades ago, before modern breeding, tomatoes were much more likely to be plagued by horticultural defects and rot, he said.

"The tomato lovers waxing poetic about heirloom tomatoes and the good ol' days," Rabin said, "are usually not the actual farmers who had to grow them, or the deli owners who had to throw one-third of them out."


Contact staff writer Tom Avril at 215-854-2430 or tavril@phillynews.com .

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