Digestion of raw banana starch in the small intestine of healthy humans: structural features of resistant starch.

The digestion of freeze-dried green banana flour in the upper gut was studied by an intubation technique in six healthy subjects over a 14 h period. Of alpha-glucans ingested, 83.7% reached the terminal ileum but were almost totally fermented in the colon. Structural study of the resistant fraction showed that a small part of the alpha-glucans which escaped digestion in the small intestine was composed of oligosaccharides from starch hydrolysis, whereas the rest was insoluble starch in granule form with physical characteristics similar to those of raw banana starch. Passage through the small intestine altered granule structure by increasing susceptibility to further alpha-amylase hydrolysis. Compared with resistant starch values in vivo, those obtained with the in vitro methods tested were inadequate to estimate the whole fraction of starch reaching the terminal ileum.