Preparation and Analysis of α-1,6 Glucan as a Slowly Digestible Carbohydrate

Carbohydrate materials that produce lower postprandial blood glucose increase are required for diabetic patients. To develop slowly digestible carbohydrates, the effect of degree of polymerization (DP) of α-1,6 glucan on its digestibility was investigated in vitro and in vivo. We prepared four fractions of α-1,6 glucan composed primarily of DP 3-9, DP 10-30, DP 31-150, and DP 151+ by fractionating a dextran hydrolysate. An in vitro experiment using digestive enzymes showed that the glucose productions of DP 3-9, DP 10-30, DP 31-150, and DP 151+ were 70.3, 53.4, 28.2, and 19.2 % in 2 h, and 92.1, 83.9, 39.6, and 33.3 % in 24 h relative to dextrin, respectively. An in vivo glycemic response showed that the incremental area under the curve (iAUC) of blood glucose levels of α-1,6 glucan with DP 3-9, DP 10-30, DP 31-150, and DP 151+ were 99.5, 84.3, 65.4, and 40.1 % relative to dextrin, respectively. These results indicated that α-1,6 glucan with higher DP had stronger resistance to digestion and produced a smaller blood glucose response. DP 10-30 showed significantly lower maximum blood glucose levels than dextrin; however, no significant difference was observed in iAUC, indicating that DP 10-30 was slowly digestible. In addition, α-1,6 glucan was also produced using an enzymatic reaction with dextrin dextranase (DDase). This produced similar results to DP 10-30. The DDase product can be synthesized from dextrin at low cost. This glucan is expected to be useful as a slowly digestible carbohydrate source.