Multi-scale structural and digestion resistibility changes of high-amylose corn starch after hydrothermal-pressure treatment at different gelatinizing temperatures

Abstract

The effects of gelatinizing temperature on the starch enzymatic digestion resistibility and the changes in the multi-scale structures (molecular molar mass and its distribution, molecular ordered structure, crystalline structure, lamellar structure, and granular fractal structure) of a high-amylose corn starch induced by hydrothermal-pressure (HP) processing were investigated, and the gelatinizing temperature – starch structure – digestion resistibility relationships were revealed by the combination of GPC-MALS, ATR-FTIR, XRD, DSC, and SAXS techniques. The results indicate that the short-range orders on the granular surface, the crystallinity, and the total enthalpy should not be the ultimate determinants of the resistibility against enzymatic digestion of the HP-treated starch. The degraded starch molecules with the molecular molar mass between 4×105 to 4×106g/mol, a higher degree of the helical ordered structures of the complexes between the degraded amylose molecules and the lipid and of the complexes between the degraded amylose molecules, a newly formed repeat aggregation structure with about 18–15nm thickness, a great amount of the ordered amylopectin crystalline lamellae, and a mass fractal structure in the length scale of 18.5<d<78.5nm, all contributed to the greater resistibility against enzymatic digestion of the HP-treated starch. It was the more ordered starch molecular aggregation architecture which came from the multi-scale structural changes after the HP treatment that could be more difficult for starch enzymes to attack the active sites of starch molecules, resulted in a higher content of resistant starch.