Cotton is grown for its fibres, by more than 20 million farmers. With the exception of the US and Australia, it is primarily cultivated as a cash crop in developing countries, particularly parts of Asia and Africa where malnutrition and starvation are rife.
Cottonseed is a protein rich by-product of the textile industry, around 1.65kg of which is left over for every 1kg of cotton fibre. But because it is also high in gossypol, a toxin that causes heart and liver damage and male sterility in monogastric animals, until now this abundant protein source has remained untapped for human nutrition.
If the seed were safe for consumption, the 44m metric tonnes produced each year, of which 9.4m MT is protein, would meet the protein requirements of half a billion people (50g per day), researchers from Texas A&M University will report in next week's Proceedings of the National Academy of Scientists (Nov 28 2006, vol 103, no 48, 18054-18059).
The researchers, led by Keerti Rathore, used RNA interference to disrupt gossypol biosynthesis in cottonseed tissue, by interfering with the expression of the d-cadinene synthase gene during seed development.
This, they report, led to a reduction in gossypol in the seeds to around 200 parts per million (ppm), while the levels in the foliage and floral parts of the plant were not affected.
The FDA considers it to be under 450 parts per million (ppm), whereas the WHO and FAO set the bar higher, at 600 ppm.
Gossypol-free cotton has been something of a holy grail for plant geneticists for decades, since researchers in the 1950s developed "glandless cotton", lacking the glands that generate gossypol, using conventional breeding techniques. However this proved to be commercially unviable, since the absence of gossypol in the foliage meant the plants were stripped of their defences to insect pests.
"Thus, the promise of cottonseed in contributing to the food requirements of the burgeoning world population remained unfulfilled," wrote the researchers.
Rathore told NutraIngredients.com that no commercial deal has been made with respect to the discovery, and the decision to commercialise lies with the university.
At present, as much as 50 per cent of cottonseed from the US is used by the food industry, but only after it has been processed to remove the gossypol from the oil. The oil is then used in food products and for cooking - and indeed, is appreciated for its flavour - while the remaining protein-rich meal is used as livestock feed.
Ruminants' second stomachs contain bacteria that break down the gossypol, so it is not toxic for them. "However cows are the most inefficient animals in converting feed to meat and milk," said Rathone. "If there is no gossypol, cottonseed could be directly used for feed".
The research may ultimately make cottonseed can be a new source of protein for people in developing countries. Crucially, it could be grown locally, so there would be no need for complex distribution networks.
Moreover the same approach may also be viable to make other plants safer for human consumption - such as Lathyrus sativus beans that are commonly eaten by poor people in Asia and Africa despite the presence of a neuroxin that can lead to a form of spastic paraparesis.
Cassava and fava beans could also be made safer, with the removal of cyanogenic and fava glycosides, respectively.
"An approach based on the removal of naturally occurring toxic compounds from the edible portion of the plant not only improves food safety but also provides an additional and potentially extraordinary means to meet the nutritional requirements of the growing world population without having to increase either crop yields or acreage planted," the researchers wrote.