Glucose absorption from starch hydrolysates in the human jejunum

The intestinal absorption and mucosal hydrolysis of a partial and a complete alpha-amylase hydrolysate of corn starch, simulating the normal intermediary and end products of luminal starch digestion, was studied using an in vivo steady state jejunal perfusion technique in normal human subjects. Alpha-amylase was excluded from the test segment by proximal balloon occlusion. Products of hydrolysis during intestinal perfusion were identified using gel permeation chromatography. Three isocaloric, isotonic sugar saline solutions containing 140 mM glucose, 70 mM maltose and the partial amylase hydrolysate of starch (51.5 +/- 1.4% of glucose content comprising glucose polymers of more than 10 glucose units) were perfused in the first study. Net glucose absorption during perfusion of the partial hydrolysate and free glucose was similar, but significantly faster from maltose (p less than 0.05). Hydrolysis of the polymer fraction containing more than 10 glucose units was significantly slower (29.5 +/- 2.0% of infused load) than the lower molecular weight fraction (56.4 +/- 3.8%, p less than 0.001). As net glucose absorption from the partial hydrolysate was similar to that from glucose, despite the slow hydrolysis of the higher molecular weight fraction, it seemed likely that oligosaccharides in the more rapidly hydrolysed lower molecular weight fractions were exerting a kinetic advantage on glucose absorption. This was confirmed in a second study, where glucose absorption from a complete amylase hydrolysate consisting predominantly of maltose, maltotriose and alpha-limit dextrins, occurred significantly faster (81.8 +/- 4.8 mmol/h/25 cm) than from isocaloric free glucose (55.8 +/- 4.9 mmol/h/25 cm, p less than 0.001). Chromatograms of intestinal aspirates suggested that (1->4), but not 1->6) linked oligosaccharides liberated during luminal and brush-border hydrolysis of dietary starch conferred a kinetic advantage on glucose absorption.