Abstract

SIVOLI, Lilliam; PEREZ, Elevina; LARES, Mary  and  LEAL, Edgardo. Studies of conformational changes, crystalline and granular structures, and in vitro digestibility of cross-linked and methylated corn starches. INCI [online]. 2009, vol.34, n.1, pp.052-056. ISSN 0378-1844.

Starch granular ultrastructure is an important determinant of its functional properties. Its knowledge, control and application should help to produce a wide range of food products. The goal of the study was to measure the modifications produced by cross-linking and methylation on the conformation and the granular and crystalline structures of corn starch, as well as the effects on the in vitro enzymatic digestibility of starch by a-amylase. Cross-linked and methylated starches were produced from commercial corn starch by low degree substitution (DS) methods. Both native and modified starches were analyzed employing NMR, SEM and X-ray diffraction. The morphologic characteristics, crystalline structure and susceptibility to hydrolysis by a-amylase were dramatically affected by the methylation process, while cross-linked corn starch showed non-significant variations that did not change the type A pattern of the native one. However, the ¹³C CP-MAS NMR spectrum of the cross-linked starch is suggesting a change from a type A to a type B crystalline pattern, while the X-ray diffraction pattern of the methylated starch was completely different from those reported in the literature for any starches. No changes in granular shape were observed (SEM) in the cross-linked starch, while the methylated starch showed larger chunks without granular integrity and with a rough surface due to exo-erosion. It can be presumed that, due to the presence of methyl groups inside the granules, the enzyme-substrate interaction is hindered by steric effects.

Keywords : Corn Starch; Cross-Linking; Crystalline Structure; Granular Structure; In Vitro Digestibility; Methylation.