A sugarfree beet that tastes just as sweet.

Dutch researchers have grown genetically engineered sugar beets that transform their sucrose into fructan molecules, which serve as a low-calorie sweetener. The beets could become an inexpensive way to manufacture fructans commercially.

Fructans are polymer chains of the sugar fructose, but human enzymes can't easily digest them, so they contribute few dietary calories. Today, manufacturers either synthesize fructans biochemically or isolate them from plants such as chicory and Jerusalem artichokes. Fructans haven't found a large market, however, because the manufacturing methods are expensive and the plants yield little product.

Sugar beets, on the other hand, churn out lots of sucrose. Hoping to take advantage of the beets' efficient biochemical machinery, researchers from the Netherlands Organization for Agricultural Research in Wageningen transplanted the Jerusalem artichoke gene for making fructans into the sugar beet. The gene codes for an enzyme that converts molecules of sucrose, each consisting of one glucose and one fructose unit, into fructan polymer chains. The team reports its achievement in the September Nature Biotechnology.

The genetically altered beets transform 90 percent of their sucrose into short fructans, each being two to four fructose units in length, the ideal size for sweeteners. "Through addition of extra fructan genes, sugar beets can also be induced to synthesize other fructans, like long-chain, branched fructans," says study coauthor Andries J. Koops. "All these fructans may have different applications or market potentials."

Larger fructans "have an interesting mouth feel, so you can use them in emulsions instead of fat," says Martina McGloughlin, director of the biotechnology program at the University of California, Davis. They could find uses in low-calorie ice cream and spreads, she suggests (SN: 9/5/98, p. 157).

The Dutch team also is pursuing the "plant as factory" concept for other food products and chemicals, Koops says.

It remains to be seen whether fructan beet production can be scaled up to commercial levels, McGloughlin cautions, but getting efficient synthesis is "a big step forward."