Effect of oxidation, cross-linking and dual modification on physicochemical, crystallinity, morphological, pasting and thermal characteristics of elephant foot yam (Amorphophallus paeoniifolius) starch

Elephant foot yam starch was chemically modified using sodium hypochlorite (NaOCl) and sodium trimetaphosphate (STMP), for the preparation of oxidized (OYS), cross-linked (CYS) and dual modified i.e. oxidized cross-linked (OCYS) and cross-linked oxidized (COYS) starches. Characteristics analyzed such as pasting, morphological, thermal, FTIR and XRD analysis indicated modification of starch which was further authenticated by determining the degree of cross-linking (20.5%), carbonyl (0.014–0.07%) and carboxyl content (0.04–0.14%). Modification significantly (P ≤ 0.05) improved water binding capacity and color value (whiteness) of starches. Temperature showed a positive effect on swelling power and solubility of native and modified starches, however in cross-linked starch the swelling power decreased. Paste clarity (%T) highly improved with oxidation and dual modification and decreased for cross-linked starch. A significant reduction in amylose content was observed following modification except for cross-linked starch. Increase in degree of crystallinity of oxidized and dual modified starches was depicted from X-ray diffractogram. Decrease in viscosity profile of modified starches was observed using Rapid Visco Analyzer (RVA) with no gel paste formation occurred for oxidized cross-linked starch. Studies on the phase transitions associated with gelatinization using DSC showed higher enthalpy values (ΔHgel) for cross-linked and dual modified starches as compared to native and oxidized starch. The morphology of the starch granules presented surface fissures in case of oxidized and oxidized cross-linked starch, whereas smooth surface of native, cross-linked and cross-linked oxidized starches was observed.