Structural characterization of starch networks in the solid state by cross-polarization magic-angle-spinning carbon-13 NMR spectroscopy and wide angle x-ray diffraction

Abstract

The changes in structure and morphology following network formation of pregelatinized starch were studied in the solid state by cross-polarization magic-angle-spinning 13C NMR spectroscopy and wide angle X-ray diffraction. Two types of mechanisms for network formation were employed, complexation with calcium and covalent cross-linking with epichlorohydrin. The spectra lines of the amylose network prepared by the calcium procedure were very narrow, and fine splitting was observed, indicating the formation of helical structure. The spectra lines of the network formed following the addition of epichlorohydrin were very broad and almost structureless, indicating that the resulting network is highly disordered and largely amorphous. These observations are supported by wide angle X-ray diffractograms. Changes in C-6 chemical shift was observed following starch complexation with calcium, whereas following the reaction with epichlorohydrin, only minor changes in spectra pattern were observed. The amylose network formed by the calcium procedure is of physical character, whereas a covalently cross-linked network was formed by the reaction with epichlorohydrin. These differences in structure have been observed to manifest themselves in the enzymatic degradation rates of these networks.

Characterization of dextrin hydrogels by FTIR spectroscopy and solid state NMR spectroscopy

“…The spectrum of original dextrin (Fig. 5a, bottom) shows the profile expected with basis on previous reports for starch-based polysaccharides [24][25][26]. The central band at 72 ppm accommodates the overlapped contributions from C2, 3, 5 and ordered C4 environments [26].…”

Modification of Pea Starch and Dextrin Polymers with Isocyanate Functional Groups

“…The overlapping signal at around 68–78 ppm is collectively associated with C 2 , C 3 , and C 5 [2,29]. Glycosidic carbons C 1 and C 4 profiles are most sensitive to chain conformations [30], and therefore the resonances that appear at 81.4 and 103.2 ppm are due to the amorphous domains of the C 4 and C 1 , respectively [2,31]. Modification of starch and dextrin with IPDI caused apparent changes on NMR spectra, and the intensity of signals was more pronounced at the high NCO:OH ratio (6:1).…”

Microhardness and water sorption in injection‐molded starch

“…However, as excess energy of evaporation is actually observed to increase with decreasing water content, this excess was attributed to changes in the starch matrix on addition or removal of water molecules. 8 In preceding studies,14, 15 the analysis of the X‐ray diffraction patterns of processed starch offered a possible explanation about the structural changes occurring on injection‐molded materials as a function of temperature. Accordingly, the first interval ( H increase) can be associated to a transformation of the majority of single helices into a network structure of double helices.…”