Enzyme-Synthesized Highly Branched Maltodextrins Have Slow Glucose Generation at the Mucosal α-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(8) Da, BE-WCS: 2.76x10(5) Da, and BEBA-WCS 1.62x10(5) Da), and changes in linear chain distributions (WCS: 21.6, BE-WCS: 16.9, BEBA-WCS: 12.2 DPw). 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.