Although many forms of carbohydrates in nature are polymers of glucose and galactose, most of these carbohydrate macromolecules cannot be used as a nutritional energy source by animals because they lack the required digestive enzymes. For example, humans and nonruminating livestock do not have the α-galactosidase enzyme required to cleave the α(1S6) glycosidic bond present in stachyose, a raffinose-series oligosaccharide contained at high levels in beans. This can sometimes cause a problem when beans are consumed because the human and nonruminating livestock digestive tracts contain bacteria that express the α-galactosidase enzyme and are able to metabolize stachyose and other oligosaccharides. If these bacterial fermentation processes occur at a high rate, then the large amount of methane gas and sulfur-containing compounds produced will cause bloat and flatulence.
Everyday BioChem 