Chemistry Studies in Siena 2012: Rotten Tomatoes

Supermarket tomatoes do not taste as good as they used to be. As I was browsing through the news on a Saturday morning, I came across an interesting article describing new research that had identified why tomatoes have lost their flavor over the past years. With this new knowledge, scientists may eventually be able to recreate the flavor that had once been present in the tomato population. The answer lies in the genes.

About 70 years ago, tomato growers began mass producing the variety of tomatoes that we see today: uniformly colored, light green tomatoes that eventually ripen into uniformly colored red tomatoes. Since most of us are around 20 years old, it’s difficult to imagine how much better tomatoes used to taste because we’ve never had it. You can still get tomatoes of the “traditional” variety, but they come from small farms and are usually more expensive or rarer. Tomatoes used to have splotches of different shades of green and red. The advantages they saw in the new, uniform color mutation was that it made the tomato look more visually appealing and easier to identify as ripe during the harvesting season. However, an unintended consequence occurred. Tomatoes unexpectedly lost their flavor.

Fruits and vegetables use photosynthesis to convert energy from the sun into sugars that the plant can use for food. Scientists focused on two genes in tomatoes that are responsible for this: GLK1 and GLK2. The two genes help signal the production of chloroplasts, or the plant structures that undergo photosynthesis. While GLK1 works exclusively in the leaves of the plant, GLK2 is active in both the leaves and the fruit of the tomato plant. Most of the sugar of the fruit, about 70-80%, comes from the leaves of the plant, but the rest of it is produced by the fruit itself – providing that the tomato has the GLK2 gene.

As you might be able to guess, the tomato growers unintentionally bred out the GLK2 gene when they preferentially selected the tomatoes with uniformly light green skins. Modern tomatoes were missing this gene that helped the fruit produce more sugar. To try and see if they could reproduce tomatoes of the old, splotchy and darker-green variety, scientists genetically engineered modern tomatoes with the GLK2 gene. What they found were tomatoes that were not only 40% higher in sugar content, but also had 20% more carotenoids. Lycopene, which is the primary carotenoid found in tomatoes, has known health benefits in the form of anti-cancer, antioxidant properties. So in addition to being tastier, the genetically modified tomatoes are also healthier. Unfortunately, the researchers who conducted this study (Powell et al., 2012) were unable to actually taste test their creation due to regulations, so more (tasty) tests are needed to qualitatively confirm the success of their experiment!