| 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
|
