Optimize the nutrition from onions.

The onion, famous for causing eyes to water and digestive systems to rumble, is being primed for a makeover. USDA-ARS plant geneticists are trying to bring out the best in onions--their heart-healthy compounds, antioxidants and soluble fiber--while still retaining what consumers love most about the vegetable: its sweet, mildly sharp taste.

Researchers want to develop an onion that's mild in taste but still full of heart-healthy nutrients. Before they can do this, though, they must pinpoint the genetic differences between sweet onions and carbohydrate-dense ones.

Scientists consider onions to be one of the most important health-promoting functional foods. They contain three different groups of health-enhancing compounds: thiosulfinates, fructans and flavonoids. The thiosulfinates that give onions their pungency are also a great boon to the body's bloodstream. The vegetable world's answer to aspirin, these blood-thinning compounds can break down platelets that might otherwise form troubling plugs at sites of vascular damage. Fructans are a source of soluble fiber shown to reduce the potential for colorectal cancer. And flavonoids, such as quercetin, have antioxidant activity.

But to get optimal amounts of these beneficial compounds, onion lovers need to consume denser, more pungent varieties. The popular sweet and mild onion varieties contain a lot of water, which dilutes their nutrient content. To help package all of the onion's desirable taste and nutrient qualities into one bulb, researchers are trying to determine which genes are linked to various healthful nutrients. In a recent paper published in the journal Theoretical and Applied Genetics, ARS researchers reported on a valuable gene that appears closely involved in fructan accumulation. They've identified its effect and mapped it, placing it on onion chromosome 8. The more fructans there are, the more heart-healthy thiosulfinates there'll also be in the product.

Investigators also discovered a gene that helps elevate sucrose concentrations in onion bulbs. This means it may be possible to boost the onion's natural sweetness while increasing the carbohydrates linked to good health. The major limiting factor is the onion's sluggish reproductive cycle. It takes two years to get a new generation of onions after performing a cross between two plants.

Because onion is a biennial, the scientists hope to produce an inbred in the next four to five years, which would then go to hybrid seed production, which would take another eight to 10 years.

Further information. Michael Havey, USDA-ARS Vegetable Crops Research Unit, Department of Horticulture, University of Wisconsin-Madison, 1575 Linden Dr., Madison, WI 53706; phone: 608-262-1830; fax: 608-262-4743; email: mjhavey@facstaff.wisc.edu.