In 1992, a pair of scientists had a brainwave: How about inserting genes into rice that would boost its vitamin A content? Tens of millions of poor people who depend on rice as a staple could receive the vital nutrient, potentially averting hundreds of thousands of cases of blindness each year.

The idea for what came to be called "golden rice" - named for its bright yellow hue - was proclaimed as a defining moment for genetically modified food.

Backers said the initiative ushered in an era when GM crops would start to help the poor and malnourished, rather than benefit only farmers and biotech firms.

"It's a humanitarian project," said Ingo Potrykus, professor emeritus at the Swiss Federal Institute of Technology, one of the co-inventors of golden rice.

Yet the rice is still a long way from appearing in people's bowls. The date estimated for commercialization is 2016, provided the novel product gets the go-ahead from government regulatory authorities.

With $30 million invested so far, the odyssey speaks tellingly of the technical, regulatory and commercial hurdles that have beset the dream of biofortified food.

First, it took scientists years to find and insert the two genes that modified the metabolic pathway in rice to boost levels of beta-carotene, the precursor to vitamin A.

After that came the bio-safety phase, to see if the rice was safe for health and the environment, and to discover whether beta-carotene levels in lab plants could be replicated in field trials in different soils and climates.

There were also bio-efficacy experiments to be conducted, to see whether the rice did, indeed, overcome vitamin deficiency, and whether volunteers found the taste acceptable.

All these tests are still unfolding in the Philippines, Indonesia and Bangladesh, said Bruce Tolentino, deputy director-general of the Philippines-based International Rice Research Institute.

"We have been working on this for a long time and we would like to have this process completed as soon as possible," he said.

But "it depends on the regulatory authorities. That is not under our control".

Antonio Alfonso at the Philippine Rice Research Institute, which partners with IRRI in the not-for-profit development of golden rice, said "it will be two or three more years before we can apply for commercialization".

The rice's yield may also have to be tweaked to boost its appeal to farmers, whose buy-in is essential, he said.

'Fool's gold'

Environmental groups are defiant about GM-fortified foods. Some have dubbed golden rice "fool's gold".

Greenpeace, the most vocal and influential of the critics, says the risks of GM contamination to other plants and impacts on health may not emerge for years.

There are also suspicions that developing countries are being used as a technological test bed - and contentions that malnutrition will not be ended by a magic bullet fired from a gene lab.

"This whole vitamin A issue is a red herring," said Janet Cotter, a scientist with Greenpeace at the University of Exeter in southwestern England.