Determination of the structural changes by FT-IR, Raman, and CP/MAS ¹³C NMR spectroscopy on retrograded starch of maize tortillas

The nixtamalization, production and storage of tortillas in refrigeration cause several changes on the starch structure, resulting in an increased crystallinity and therefore a higher content of resistant starch. The IR analysis for resistant starch (RS) showed a band at 1047 cm^-1 associated to the retrogradation process; this band was due to the weakening of the intermolecular H-bonds. These associated together to form ordered regions. The Raman analysis shows a characteristic band at 856 cm^-1 corresponding to C-C skeletal modes of glucose of α-1,4 glycosidic linkage starches, and a band at 480 cm^-1 attributed to skeletal vibrations of the pyranose ring in the glucose unit of starches. These changes may be related to the polymerization degree of the starch molecules, as well as to the retrogradation of amylose and amylopectin. The spectrum of ¹³C CP-MAS/NMR for RS3 supports the results obtained by IR and Raman. Lipidic and proteic groups were observed which may be in the form of complexes with amylose. One can proclaim that the existence of the salt form is induced and stabilized by the interactions dominating the V amylose structure in the solid state.