We broke the tomato, and we’re using science to fix it

We’ve bred tomatoes for high productivity with no regard for their taste.

John Timmer – Feb 19, 2013 7:30 am | 129

Canned tomato labels. Credit: lgsinden

Thanks to decades of breeding, the modern agricultural tomato has a lot of properties that are great for farmers: the plants are incredibly productive, and the resulting tomatoes hold up well to shipping. Just one small problem: they are nearly tasteless. Heirloom tomato strains have become available precisely because people aren’t especially interested in the mass-produced, modern tomato.

In the words of a panel at the meeting of the American Association for the Advancement of science, we “broke” the tomato by allowing the plant breeders to respond to the needs of farmers, instead of the tomato’s end-users: consumers. As a result, their breeding has produced a product that most people don’t actually enjoy eating. And that’s a public health issue, given that tomato-rich diets have been associated with a variety of beneficial effects.

Fortunately, the panel featured a number of people who are trying to fix the tomato using up-to-date biochemistry and genetics.

Yale’s Linda Bartoshuk set up the challenge with a little experiment: everyone in the audience was given a raspberry Jelly Belly. Bartoshuk had people hold their nose, then start chewing on the candy. For me, it tasted generically sweet. When, on her instructions, I released my finger, there was a sudden explosion of flavor, a lot of it evocative of raspberries—and a sudden murmur from the audience suggesting they were experiencing something similar.

What’s going on? A lot of our experience of flavor really does come from smell, but not from breathing in; instead, volatile chemicals disperse out of the back of your mouth, with some of them reaching your nasal passages. Not only can these volatiles convey a distinctive flavor, but they can also interact with flavors sensed by the tongue, enhancing or suppressing sweetness, saltiness, etc.

Harry Klee of the University of Florida has put together a collection of over 200 tomatoes, some heirloom, some the mainstream agricultural strains. Using those, his team has characterized the volatile chemicals present in each, coming up with a list of about 68. They’ve also put about 100 of those tomatoes to the test with a panel of tasters, who rated their appeal and flavor. (One of the things he discovered is that some heirloom strains are “really not very good.”)

The result is that the team has what you might consider a statistical recipe for a good tomato. Generally, what consumers like is perceived sweetness (though other factors also played in, like saltiness and tartness). And in general, the perceived sweetness was roughly in line with the amount of sugar present. But only roughly. Klee pointed out two varieties (Matina and Yellow Jelly Bean) that had similar levels of sugar, but one was perceived as twice as sweet as the other—the one with slightly less sugar.

The difference: the concentration of various volatiles in the tomatoes which are quite often derivatives of carotenoids, chemicals most closely associated with carrots. The derivatives were considered fruity and floral, and were correlated with both perceived sweetness and likability. Fortunately, the pathways that convert the carotenoids into these derivates are fairly well understood, and the authors leveraged some genetics. Tomatoes with knockouts of the genes involved in creating these derivatives were tested with consumers, and these confirmed that the resulting fruit were rated as lower sweetness.

Klee’s team has started identifying alleles that enable production of a variety of volatiles in heirloom strains, and started introducing them into high production commercial strains. According to him, a single cross can give heirloom flavor with double the yield of the original heirloom strain—not enough to get commercial growers to switch, but a step in the right direction. Further breeding and, if necessary, some genetic engineering may return the heirloom genes, along with some taste, to the modern tomato.

Then they’ll just have to get to work on the texture…