Digestibility of isomaltooligosaccharides by rats and effects on serum lipids

Isomaltooligosaccharides (IMO), a mixture of α-1, 6-glucosides, are produced enzymatically from starch for use as a new sweetener. They are a growth factor for human intestinal bifidobacteria. The effects of ingestion of IMO for 35 days on growth, organ weight, serum lipids, and saccharidase activities of rat jejunal mucosa were investigated. The digestibility of IMO was measured in models of the digestion system containing artificial gastric acid, rat intestinal mucosa, or human salivaric or hog pancreatic α-amylase. The ratios of body weight gain/food intake of the test chows suggested that the energy available to rats in IMO was about 80% that of maltose and sucrose. The serum levels of triacylglycerol and nonesterified fatty acids were significantly lower in rats fed 20% IMO. These results were similar to those obtained in rats fed chow containing fructooligosaccharide, which is nondigestible in the upper intestine and fermentable in the lower. The long-term ingestion of IMO did not induce isomaltase activity in the rat jejunal mucosa. IMO was not hydrolyzed by the in vitro digestion system except in the model containing rat intestinal mucosa. The hydrolysis ratio of IMO by rat intestinal mucosa was much lower than that of maltose or isomaltose. The results suggested that IMO is partly hydrolyzed by the enzyme of intestinal mucosa, but that the residual undigested part passes down to the lower intestine.