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Pure brew By Andy Coghlan

Pure brew By Andy Coghlan

By Andy Coghlan
the world's first caffeine-free coffee
plants will be planted this summer in a greenhouse in Hawaii. If all goes to plan, beans from the plants will not need to be decaffeinated chemically in processes which can damage beans and spoil their flavour. "I'm expecting my first sip of decaffeinated coffee from them in around 20 months," says John Stiles, who developed the beans at the University of Hawaii in Manoa. Stiles, who last week attended a meeting of the International Scientific Association of Coffee in Paris, says the altered plants are growing as tissue cultures in the laboratory. "We expect to plant them in the greenhouse in three months' time," he says.

Stiles and his colleagues had earlier identified the master gene that governs caffeine production. The gene makes xanthosine-N7-methyl transferase, the enzyme that kick-starts caffeine production.

To silence the gene, Stiles used a bacterium, Agrobacterium tumefaciens, to shuttle an antisense gene into embryonic tissue. Antisense genes are back-to-front versions of a target gene, and block its function. Stiles attached the antisense gene to genetic switches that would make it active throughout the coffee plant. Sure enough, the plants produced just 3 per cent of the normal amount of caffeine.

Stiles says the gene had to be silenced throughout the plant because in earlier studies, he found the coffee beans didn't produce much of the enzyme. He suspects that early stages of caffeine production take place elsewhere, possibly in the leaves, only later concentrating in the beans.

Some wild species of coffee contain no caffeine. But Stiles is the first to make a virtually caffeine-free variety of a commercial species--Coffea arabica. This accounts for 60 per cent of all coffee consumed.

Coffee is normally decaffeinated by treating the beans either with hot water or with supercritical carbon dioxide. "They can damage the beans, and are not completely specific for caffeine, eliminating some flavour compounds too," says Stiles. He now hopes to develop caffeine-free tea, as the same gene controls caffeine production in tea.

From New Scientist, 21 March 1998