Cold plasma pretreatment enhances OSA esterification efficiency in Kodo millet starch: Morphological, structural, rheological, and functional insights

Abstract

In this study, Kodo millet starch (KMS) was modified using multipin atmospheric cold plasma treatment at different voltages (10, 20, and 30 kV) and durations (5 and 10 min), followed by esterification with octenyl succinic anhydride (OSA). The combined modification influenced the morphological, structural, pasting, rheological, and functional properties of starch. Cold plasma prior to esterification significantly increased the degree of substitution from 0.0072 to 0.0274, whereas the amylose content decreased from 30.58 % in native starch to 14.37 % in OSA-modified cold plasma-treated starch (10 kV-5 min). Despite treatment, the granules retained their irregular and polygonal shapes but presented increased surface roughness and particle size. The zeta potential improved (−10.12 to −16.18 mV), indicating good stability. FTIR and XRD revealed minimal alterations in the functional groups and crystalline structure, although the crystallinity decreased from 29.65 % to 23.75 %. Pasting analysis showed varied viscosities and reduced pasting temperatures (86.6 to 82.3 °C). All gels exhibited non-Newtonian behavior with dominant elastic over viscous behavior. The functional properties revealed increased oil absorption (0.78 to 1.64 g/g) but reduced water absorption (1.85 to 1.32 g/g), swelling, and solubility. Syneresis analysis confirmed lower retrogradation due to reduced water expulsion. Overall, cold plasma followed by esterification improves the DS at lower OSA concentrations, making dual-modified starch suitable as an emulsifier.