Flatulence caused by soya and its control through processing

Abstract

Elimination of flatulence is a challenging practical problem associated with the comsumption of soybeans as well as other food legumes and other selected foodstuffs. The problem is compounded by the variability in susceptibility among individuals. Research has established that the oligosaccharides—verbascose, stachyose, and raffinose—are the major cause of soybean flatulence. They escape digestion and are fermented by intestinal microflora to form excessive amounts of carbon dioxide and hydrogen. Hot water treatment, aqueous alcohol extraction, and isoelectric protein precipitation processes have been adapted to produce flatus-free products commercially. At the household level, soaking combined with germination appears to be a practical means of producing soybean sprouts having low flatus activity. Food legumes, which include some oil-seeds, peas, and beans, as well as selected vegetables, contain enough of the oligosaccharides—verbascose, stachyose, raffinose—to be a major cause of flatulence in humans and animals. In the absence of alpha-galactosidases in the mammalian intestinal mucosa, these oligosaccharides escape digestion and are not absorbed. As a consequence, the active microflora in the ileum, colon, and fecal matter of the large intestine ferment them to form excessive levels of rectal gas, primarily carbon dioxide and hydrogen. In some instances, undigested starch and other carbohydrates contribute to the flatulent effect of diets. With 70% of the world’s population being lactase-deficient (hypolactasia), susceptibility to flatulence would be more widespread with diets containing both food legumes and milk products.

Use of food additives, antibiotics, and phenolic compounds to inhibit flatulence is not a practical approach. However, soya processing technology used to manufacture protein concentrates and isolates can be adapted to produce flatus-free products from other food legumes. Hot water treatment, aqueous alcohol extraction, or isoelectric protein precipitation insolubilizes most of the protein and removes the oligosaccharides. Tempeh and tofu are two other soya products that exhibit little or no flatus activity. Soaking, fermentation, enzymatic hydrolysis, and germination can also be used to eliminate oligosaccharides. Tests with humans and rats indicate that a combination of such processes can be used to reduce flatus activity. The beneficial effects of germination on flatulence, often conflicting and contradictory, have been attributed to failure to control conditions that ensure removal of most of the oligossaccharides. Whether the high-molecular-weight soybean polysaccharides (dietary fiber), which normally do not cause flatulence, can be modified during germination to become substrates for flatus production by the intestinal microflora is not known. Such an effect could compensate for the loss of stachyose and raffinose.