Oligosaccharides of Food Legumes: Alpha-Galactosidase Activity and the Flatus Problem

The raffinose family of oligosaccharides--including stachyose and verbascose--occurs in seeds of food legumes at levels that cause flatulence in man and animals. These carbohydrates escape digestion because there is no α-galactosidase activity in mammalian intestinal mucosa and because they are not absorbed into the blood. Consequently, bacteria in the lower intestinal tract metabolize them to form large amounts of carbon dioxide and hydrogen and to lower the pH. The amount and pattern of expelled gases reflect differences in type, location, and abundance of intestinal microorganisms possessing α-galactosidase activity in a favorable nutrient environment. Water and aqueous alcohol extraction, as well as enzymatic hydrolysis, can be used to process food legumes into products having low flatus activity. According to in vitro and in vivo studies, antibiotics and naturally occurring substances can inhibit bacterial activity in the intestinal tract; however, it is unlikely such additives would be approved for human consumption. Breeding soybeans low in oligosaccharide content holds little promise.