Bioavailability of carbohydrates in legumes: digestible and indigestible fractions.
Despite their important contribution to seed weight, carbohydrates in pulses have received limited attention. However, experimental evidence accumulated during the last two decades indicate that legumes are rich sources of slowly digestible starch promoting moderate postprandial glycernic and insulinemic responses. Although the reasons for this phenomenon are not completely understood, some intrinsic properties of the starch itself and the microstructure of cotyledon cells appear to determine much of the slow release character. This beneficial feature is rather sensitive to thermal and mechanical processing. A minimum of 10% of the starch occurring in common beans and lentils escapes digestion and absorption in the normal small intestine, and is therefore referred to as "resistant starch". This material consists mainly of retrograded amylose fractions generated upon cooling of wet-heated pulses. Physically inaccessible starch fractions resulting from cotyledon microstructural properties may also contribute to incomplete digestibility, accounting for up to 40% of the indigestible starch. These indigestible starch fractions are fermented in the large intestine generating gases and volatile fatty acids, compounds that have important influence on the physiology of the colonic mucosa and peripheral metabolism.