Differentiated digestion resistance and physicochemical properties of linear and α-1,2/α-1,3 branched isomaltodextrins prepared by 4,6-α-glucanotransferase and branching sucrases

Isomaltodextrins (IMDs) are starch-based dietary fibers (DF) prepared enzymatically, which show great potential as a functional food ingredient. In this study, a series of novel IMDs with diverse structures were generated by 4,6-α-glucanotransferase GtfBΔN from Limosilactobacillus fermentum NCC 3057, combined with two α-1,2 and α-1,3 branching sucrases. Results indicated that α-1,2 and α-1,3 branching significantly improved the DF contents of α-1,6 linear products up to 60.9-62.8%. When altering the ratios of [sucrose]/[maltodextrin], IMDs containing 25.8-89.0% α-1,6 bonds, 0-59.6% α-1,2 bonds and 0-35.1% α-1,3 bonds and Mw ranged from 1967 to 4876 Da were obtained. Physicochemical property analysis showed that grafting with α-1,2 or α-1,3 single glycosyl branches can improve the solubility of the α-1,6 linear product, in which α-1,3 branched products were better. Moreover, α-1,2 or α-1,3 branching did no effect on the viscosity of the products but Mw did, the larger Mw the greater viscosity. In addition, α-1,6 linear and α-1,2 or α-1,3 branched IMDs all exhibited strong acid-heating stabilities, freeze-thaw stabilities, and good resistance to browning caused by the Maillard reaction. Branched IMDs showed excellent storage stabilities at room temperature for one year at a concentration of 60%, whereas 45% α-1,6 linear IMD precipitated quickly within 12 h. Most importantly, α-1,2 or α-1,3 branching remarkably increased the contents of resistant starch in the α-1,6 linear IMDs to 74.5-76.8%. These clear qualitative assessments demonstrated the outstanding processing and application properties of the branched IMDs and were expected to provide valuable perspectives toward the technological innovation of functional carbohydrates.