Chemical gelatinization of pea and chickpea starch granules in dimethyl sulfoxide: Structural and physicochemical analysis

C-type starch has a mixed crystalline structure with B-type in the central region of the granules and A-type in the periphery region, though the polymorph distribution remains to be better studied. This study used 90 % dimethyl sulfoxide (DMSO) solution as a chemical gelatinization agent to treat granular pea and chickpea starches (C-type). Morphological observations showed that the periphery layer of pea and chickpea starch granules did not undergo an ideal peeling of surface gelatinization. X-ray diffraction on granular residues indicated that more A-type starch fraction was maintained after the chemical gelatinization. The starch granules were partly gelatinized from the surface and partly gelatinized from the central region upon the disintegration of starch granules. Temperature-dependent rheological properties of the native starches showed two-phase swelling, while that of chemical gelatinized starches did not. For most starches (except for small-granule pea starch), amylose chain length was significantly shorter in the granular residues after the chemical gelatinization compared to their native counterpart. The results suggested that DMSO selectively gelatinized starch granules, in which the structure of amylose made a difference. The present study highlighted the possibility of separating A- and B-type fractions in individual starch granules.