Enzyme-Synthesized Highly Branched Maltodextrins Have Slow Glucose Generation at the Mucosal [alpha]-Glucosidase Level and Are Slowly Digestible In Vivo

For digestion of starch in humans, [alpha]-amylase first hydrolyzes starch molecules to produce [alpha]-limit dextrins, followed by complete hydrolysis to glucose by the mucosal [alpha]-glucosidases in the small intestine. It is known that [alpha]-1,6 linkages in starch are hydrolyzed at a lower rate than are [alpha]-1,4 linkages. Here, to create designed slowly digestible carbohydrates, the structure of waxy corn starch (WCS) was modified using a known branching enzyme alone (BE) and an in combination with [beta]-amylase (BA) to increase further the [alpha]-1,6 branching ratio. The digestibility of the enzymatically synthesized products was investigated using [alpha]-amylase and four recombinant mammalian mucosal [alpha]-glucosidases. Enzyme-modified products (BE-WCS and BEBA-WCS) had increased percentage of [alpha]-1,6 linkages (WCS: 5.3%, BE-WCS: 7.1%, and BEBA-WCS: 12.9%), decreased weight-average molecular weight (WCS: 1.73x10.sup.8 Da, BE-WCS: 2.76x10.sup.5 Da, and BEBA-WCS 1.62x10.sup.5 Da), and changes in linear chain distributions (WCS: 21.6, BE-WCS: 16.9, BEBA-WCS: 12.2 DP.sub.w). Hydrolysis by human pancreatic [alpha]-amylase resulted in an increase in the amount of branched [alpha]-limit dextrin from 26.8% (WCS) to 56.8% (BEBA-WCS). The [alpha]-amylolyzed samples were hydrolyzed by the individual [alpha]-glucosidases (100 U) and glucogenesis decreased with all as the branching ratio increased. This is the first report showing that hydrolysis rate of the mammalian mucosal [alpha]-glucosidases is limited by the amount of branched [alpha]-limit dextrin. When enzyme-treated materials were gavaged to rats, the level of postprandial blood glucose at 60 min from BEBA-WCS was significantly higher than for WCS or BE-WCS. Thus, highly branched glucan structures modified by BE and BA had a comparably slow digesting property both in vitro and in vivo. Such highly branched [alpha]-glucans show promise as a food ingredient to control postprandial glucose levels and to attain extended glucose release.