In Vivo Digestibility of Carbohydrate Rich in Isomaltomegalosaccharide Produced from Starch by Dextrin Dextranase

Abstract

Slowly digestible carbohydrates are needed for nutritional support in diabetic patients with malnutrition. They are a good source of energy and have the advantage that their consumption produces a low postprandial peak in blood glucose levels because they are slowly and completely digested in the small intestine. A high-amount isomaltomegalosaccharide containing carbohydrate (H-IMS), made from starch by dextrin dextranase, is a mixture of glucose polymers which has a continuous linear structure of α-1,6-glucosidic bonds and a small number of α-1,4-glucosidic bonds at the reducing ends. It has a broad degree of polymerization (DP) distribution with glucans of DP 10－30 as the major component. In our previous study, H-IMS has been shown to exhibit slow digestibility in vitro and not to raise postprandial blood glucose to such levels as that raised by dextrin in vivo. This marks it out as a potentially useful slowly digestible carbohydrate, and this study aimed to evaluate its in vivo digestibility. The amount of breath hydrogen emitted following oral administration of H-IMS was measured to determine whether any indigestible fraction passed through to and was fermented in the large intestine. Total carbohydrate in the feces was also measured. H-IMS, like glucose and dextrin, did not result in breath hydrogen excretion. Carbohydrate excretion with dietary H-IMS was no different from that of glucose or water. These results show that the H-IMS is completely digested and absorbed in the small intestine, indicating its potential as a slowly digestible carbohydrate in the diet of diabetic patients.

Keywords: breath hydrogen; digestibility; fecal excretion; isomaltomegalosaccharide; slowly digestible carbohydrate; α-1,6-glucan.

Fig. 1.. DP distribution of the H-IMS determined by high-performance liquid chromatography.

The calibration curve (dotted line) calculated from pullulan standard (dot) indicate relationship of elution time and molecular weight on the right axis. The DP distribution of the product was calculated from the area under the vertically divided curve.

Fig. 2.. Digestion profiles of dextrin and the H-IMS.

Data are shown in free glucose concentration at each time point after the addition of the digestive enzymes. Data are presented as mean ± SEM of the results obtained in quadruplicate for each measurement time.

Fig. 3.. Changes in postprandial hydrogen concentration in the internal air of the test chambers after administration to rats of either glucose, dextrin, H-IMS, or lactulose.

Data are presented as mean ± SEM. The symbols indicate the significant differences at each time point. *, glucose group vs. lactulose group; †, dextrin group vs. lactulose group; ‡, H-IMS group vs. lactulose group. p < 0.05 was considered statistically significant.

Fig. 4.. Fecal carbohydrate excretion in rats on each day after administration of either water, glucose, H-IMS, or polydextrose.

Data are presented as mean ± SEM. Asterisks indicate a significant difference between two groups on each day. p < 0.05 was considered statistically significant.