BANANA STARCH BREAKDOWN IN THE HUMAN SMALL-INTESTINE STUDIED BY ELECTRON-MICROSCOPY

Objective: To determine the origin of the poor digestibility of banana starch granules in the human small intestine. Design: The subjects re ceived the same experimental meal. Setting: Nutrition Research Unit, L aennec Hospital, CHU, Nantes. Subjects: Six healthy young subjects. In terventions: The digestion of raw green banana flour in the upper part of the gut was studied by the intubation technique. After ingestion o f 30 g banana flour mixed with a complex meal, ileal samples were cont inuously collected during 14 h. In order to determine the structural n ature of this resistant starch, the dried ileal samples were observed with scanning and transmission electron microscopy. Transmission elect ron microscopy was performed after treatment with periodic acid-thiose micarbazide-silver nitrate. Results: Banana starch proved very resista nt to in vivo amylase hydrolysis since 84% of the starch ingested reac hed the terminal ileum. The microscopic observations showed that raw b anana flour contained irregularly shaped dense starch granules with sm ooth surfaces. After their passage through the small intestine, starch granules appeared exocorroded, with porous surfaces, and some exhibit ed several irregular pits, crevices or holes by which the enzymes had penetrated and hydrolysed the inner part. Cell walls closely associate d with starch granules could have hindered enzyme access to starch. Co nclusions: Encapsulation could be partly responsible for the low diges tibility of starch in banana flour, together with the intrinsic resist ance of banana starch granules. Sponsorship: Supported by grants from the French Ministry of Agriculture and the Danone Group. Descriptors: banana, digestion, human, microscopy, small intestine, starch