Modification by α-d-glucan branching enzyme lowers the in vitro digestibility of starch from different sources

Granular corn starch, waxy corn starch, potato starch and tapioca starch were modified using the α-d-glucan branching enzyme (1,4-α-d-glucan:1,4-α-d-glucan 6-α-d-(1,4-α-d-glucano)-transferase, GBE, EC 2.4.1.18) from Geobacillus thermoglucosidans. The GBE-catalyzed modification caused a time-dependent increase in the ratios of α-1,6 linkages to total glycosidic linkages, as well as reductions in the average chain length and relative crystallinity. These modifications lowered the in vitro digestibility of the starch. Modification with GBE caused varying degrees of change in the in vitro digestibility of starches obtained from different sources. The highest slowly digestible starch (SDS) and resistant starch (RS) contents were found in modified tapioca starch. After modification of tapioca starch with GBE for 10h, the ratio of α-1,6 linkages to total glycosidic linkages was increased by 11.5%, while its relative crystallinity was decreased by 22.9%. Meanwhile, the SDS and RS contents of tapioca starch were increased by 47.3% and 13.5%, respectively. These results demonstrate that the digestibility of starch can be lowered through GBE modification, which may aid the development of modified starches that are digested more slowly.