Franklin County Master Gardener Ray Eckhart shares the latest research from scientists studying tomato flavors, with a goal of getting heirloom tomato flavor into high yielding, disease resistant varieties for commercial production. Information is from an article "Tapping Tomatoes for Taste" published in the October 2013 issue of Agricultural Research magazine.
Tomatoes are a $2 billion-a-year crop in the United States, and we demand a lot from them.
No matter where we live, we want fresh, delicious tomatoes to be available year-round. Large-scale producers ship tomatoes long distances, and that makes firmness and long-term storage top priorities for tomato breeders.
Consumers, however, value garden-fresh taste. A common complaint is that tomatoes in supermarkets lack the flavor of locally grown varieties. To improve flavor, breeders need to know more about the varieties that hold the greatest potential for enhancing taste.
Joanne Labate, an Agricultural Research Service molecular biologist, and Larry Robertson, curator of the ARS Plant Genetic Resources Unit vegetable collections in Geneva, N.Y., joined with Dilip Panthee of North Carolina State University to explore tomato's genetic diversity in a comprehensive study designed to help breeders develop tastier tomatoes.
The team raised many varieties of tomatoes and analyzed them for the compounds that help determine flavor. They also had volunteers evaluate their field-grown varieties for flavor and other sensory characteristics. The study was published in Plant Genetic Resources: Characterization and Utilization (2013).
"Commercial tomato varieties have a narrow genetic base. To find ways to improve their flavor, we need to broaden that base and begin looking among our entire stock of tomatoes for new sources of beneficial genes," Labate says.
What we refer to as "flavor" in a tomato is actually the interaction and ratio of sugars, organic acids, and volatile compounds derived from amino acids, lipids, and carotenoid precursors.
Fructose and glucose are the major forms of sugar. Citric acid is the dominant acid in ripe tomatoes, though malic acid is also present. The researchers wanted to determine the variability of these four compounds from one variety to the next and see how that variability contributes to flavor.
They grew 173 varieties on test plots in North Carolina. The varieties were selected from some 6,000 varieties that represent a cross section of the world's tomato diversity.
Some were commercial varieties, some heirlooms and others were lines used by breeders. All were part of a collection that had never been evaluated for fruit-quality traits.
Tomatoes were classified into one of three categories: plum or roma; cherry or grape; or the traditional large, round types.
Ten volunteer taste testers were trained in sensory analysis and asked to rate each variety on a scale of 1 to 5 in four sensory areas: odor, taste, flavor, and texture. The researchers also measured each variety's firmness and measured juice for levels of sugar, citric acid, and vitamin C.
A key ratio
Although thousands of compounds go into determining flavor and other characteristics, two play a key role in determining overall flavor: sugar and acid. While the amount of acid varied only slightly in the tomatoes tested (from 0.2 to 0.64 percent), there was a wide variety in sugar content (3.4 to 9.0 percent). Ror ripe tomatoes, the greater the ratio of sugar to acid, the sweeter the tomato. The sweeter the tomato, the more flavor it contains.
The findings are good news for breeders because they show a broad range of possibilities for adjusting sugar levels and developing more flavorful tomatoes.
Although all tomatoes tested were grown in the North Carolina fields, traits such as flavor are likely to show up consistently in a number of different environments, the researchers say.