Beans are an important source of nutrients such as protein, carbohydrate, insoluble fibre and a spectrum of vitamins and minerals, and are regarded as a food staple, especially in developing countries. Unfortunately beans are also often derided and avoided because eating them can lead to uncomfortable and unpleasant flatulence.
While the researchers from Simon Bolivar University in Caracas, Venezuela, were aware that flatulence is caused by bacteria in the large intestine breaking down food that has not been digested higher up in the gut.
Since the flatulence-producing elements (alpha-galactosides, raffinose, stachyoseand verbascose and soluble fibre in the case of beans) can be reduced through natural lactic acid fermentation, they set out to identify the microbial flora involved to enable this to be done on a large scale.
First, they analysed fermented black bean seeds, and identified the beneficial bacteria as being Lactobacillus casei and Lactobacillus plantarum.
They then performed back-slopping (inoculation of a new batch with a portion of an earlier successful batch) or induced fermentation and were able to reduce the levels of soluble fibre by 63.35 per cent, and raffinose by 88.6 per cent. When the samples were cooked under atmospheric pressure trypsin inhibitors and tannins - antinutritional compounds - were reduced.
What is more, the digestibility of the beans was seen both in vivo and in vitro to be improved, meaning that bean-eaters receive more beneficial nutrients.
"These results demonstrate that the lactic acid bacteria used for the induced fermentation can lead to a functional food with improved nutritional quality," wrote the researchers, led by Marisela Granito, in the Journal of the Science of Food and Agriculture (2490/05-0089), published today.
"L. casei could be used as a functional starter culture in the food industry," said Granito.
Unlocking the key to the flatulence-free bean has been something of a holy grail for some time.
A new variety of the flatulence-free manteca bean, grown in the UK, has recently come to market following decades of research by one Dr Colin Leakey.
Leakey first started looking into flatulence-free beans in the late 1960s when he was working in Uganda. He noticed that mothers were reluctant to feed their children beans because they would develop colic. This meant that they were missing out on a very valuable source of protein.
Dr Leakey found a way to make these beans - thought to be flatulence-free due to the tannins in their seed coat - suitable for the UK climate. They are now being processes and marketed under the name Prim Beans by Cambridge, UK-based Phaseolus.
Some dieticians advise that flatulence can be reduced by soaking beans prior to cooking.
But Rebecca Foster, a nutrition scientist for the British Nutrition Foundation, said she is not sure that flatulence is what puts people off beans.
"The more you eat beans, the more your digestive system gets used to them and flatulence becomes less of a problem," she said.