Abstract: Resistant dextrin (RD) prepared from corn starch by different processes vary in structure and physicochemical properties and in turn resistance to human digestive enzymes. In this research, the solubility, bond structure, digestibility and morphological structure of RD prepared by three different processes (dry heating, α-amylase, and α-amylase combined with transglycosidase) were characterized so as to explore the relationship between the quality of RD and preparation processes. The results showed that the solubility of all samples prepared was close to 100%, the water activity was less than 0.3, and the stability was good. Further strengthening the reaction conditions changed the structure of RD, resulting in the hydrolysis of α-1,4 bonds to form α-1,6, α-1,2, and β-1,6 bonds, which are the basis for digestive enzyme resistance, and the branching structure of the resulting product was mainly linked by α-1,6 and β-1,6 bonds. The enzymatic treatment changed the starch molecules from an ordered crystal structure to a disordered one, decreasing the crystallinity. After adding transglycosidase, the average branching degree (DB) increased up to 55%, and the resistance to human digestive enzymes was strongest. The results of scanning electron microscopy (SEM) and gel permeation chromatography (GPC) showed that after adding the two enzymes, repolymerization of RD occurred, the molecular weight decreased and the molecular volume increased at the same time, and gaps were formed in the molecules. This study may provide a new idea for researchers engaged in the production of RD with higher quality.

Key words: resistant dextrin; indigestibility; branching structure; transglycosidase