Sweet potato

Rcjohnsen rcjohnsen at aol.com
Mon Oct 9 22:23:57 EST 2000

Monday 9 October 2000

biotechnology : Sweet potato
See  http://helix.nature.com/nsu/001012/001012-3.html


GM researchers in France have built a potato that produces massive amounts of
fructose -- the sweetest of all natural carbohydrates -- when mashed and
heated. The sugary spuds could one day be harvested to produce the sweeteners
used in everything from diabetic chocolate to soft drinks.
Genes coding enzymes that convert starch to sugars can be spliced into the
potato plant, Rajbir Sangwan of the Université de Picardie Jules Verne in
Amiens, France, and his colleagues now report. All potatoes produce and store
starch; the enzymes in the new GM variety only convert it to fructose when the
potato is heated. So normal potato metabolism and development is not affected. 
Fructose and glucose look very similar but chemically they behave differently
-- fructose is often used as a diabetic sweetener, for instance, because it
does not seem to significantly increase the demand on insulin. Some diet
products also use it because less of it (so fewer calories) is needed to
sweeten food compared with table sugar.
Millions of tons of high-fructose syrup are produced each year in large-scale
chemical plants. Starch extracted from maize is combined with water to produce
glucose, which is then converted to fructose. In recent years, enzymes produced
by bacteria have speeded up the process.
But Sangwan's team goes one better -- bundling the entire conversion, enzymes
and all, inside a spud. They go from chemical plant to potato plant. And
scaling up the process is no problem, Sangwan points out. Just grow more
His team modify the potato by inserting genes coding the enzymes 'alpha
amylase' and 'glucose isomerase'. The first breaks down starch to glucose, the
second changes glucose to fructose. 
"The possibility of modifying the carbohydrate composition should be
particularly valuable to the food industry," Sangwan says. Potatoes heated to
different temperatures have different glucose/fructose concentrations because
of varying glucose isomerase activity, the team reports in the journal
Biotechnology and Bioengineering1. Under the right conditions, the GM potato
produces up to 20 times as much fructose as a normal spud. 
But even if fructose potatoes escape the ire of the anti-GM lobby, they will
enter a highly competitive marketplace, warns food technologist Clark Ford of
Iowa State University, Ames. "It sounds great," he says. "But fructose
production is pretty cheap and efficient already." The relative simplicity of
each conversion step means that they can be carried out on massive scales.
Still, Sangwan believes that the only obstacles blocking potential
commercialization are ethical and philosophical. Anti-GM feeling is less severe
in Canada and the United States, so he suggests that those countries may be the
first to try out the technology. And given the American public's famed love of
sugary foods, who's to say that 'French fries' won't soon take on a new and
sweeter meaning?

1.	Beaujean, A. et al. Engineering direct fructose production in processed
potato tubers by expressing a bifunctional alpha-amylase/glucose isomerase gene
complex. Biotechnology and Bioengineering 70, 9-16 (2000).

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	Nature © Macmillan Publishers Ltd 2000 Reg. No. 785998 England.

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