Pasting and rheological properties of α- amylase treated proso millet starch as affected by hydroxypropylation and cross-linking in its granular and gelatinized state

The effect of hydroxypropylation and cross-linking on the pasting and rheological properties of α- amylase treated proso millet starch in granular as well as gelatinized state was investigated. The chemical modification of enzyme pre-treated starch showed significant changes (p < 0.05) in the swelling and solubility behavior. Amylose content and water binding capacity of the starches ranged from 16.72 to 21.26% and 1.23–1.53 g/g, respectively. The pasting profile of the modified starch gel (at 6% concentration) revealed a significant decline (p< 0.05) in peak viscosity. The Herschel-Bulkley model used to characterize the steady shear properties revealed that the flow behavior was non-Newtonian pseudoplastic. The flow behavior index (n) and consistency index (K) for starch pastes at 4% concentration ranged from 0.69 to 0.91 and 0.26 to 0.77 Pa.sn, respectively, whereas at 6% concentration, the values ranged from 0.45 to 0.71, and 0.46 to 11.35 Pa.sn, respectively. Dynamic rheological characteristics demonstrated that starch pastes exhibited dominant elastic behavior. The presence of hydroxypropyl groups was confirmed by FT-IR spectroscopy, with the noticeable band stretching at OH, CH, and CO. This modification approach can be exploited to prepare proso millet starch with tailored functional characteristics for desirable food applications.