Morphology, structure and functionality of acetylated, oxidized and heat moisture treated amaranth starches

Abstract

Starch isolated from amaranth was modified by heat moisture treatment at different temperatures (85, 100 and 120 °C), oxidation and acetylation. Native and treated starches were assessed for physicochemical, pasting, gel textural, structural, thermal and morphological properties. Considerably decreased swelling power and solubility were recorded for all treated starch samples except increased swelling power in the case of acetylated starches. Modification improved paste transparency, enhancing its applicability in products where clarity of pastes is required. The increased final viscosity of amaranth starch pastes followed with hydrothermal treatment at a higher temperature (120 °C) and oxidation enhanced suitability for highly viscous end products. Decreased values of hardness, adhesiveness, gumminess and chewiness of gels observed for all treated starches except oxidized supports application potential of modified starches in products where soft gel is preferred. A new band at 1730 cm−1 in FTIR spectra of acetylated starch evidenced the addition of acetyl groups. Micrographs of starches revealed noticeable agglomeration in hydrothermally modified starches and dents on some granules of oxidized starch. X-ray diffractograms confirmed an 'A' type crystal pattern in amaranth starch which was noticed to be unaffected after modification treatments. Relative crystallinity of starch decreased following acetylation, oxidation as well as heat moisture treatment (100 °C and 120 °C). Hydrothermal treatments increased gelatinization temperatures, while chemical modification showed the opposite trend. ΔH value reduced in hydrothermally treated samples, and change in intensity was corresponding with a rise in temperature of treatment. In conclusion, physical and chemical modification treatments produced starches with diverse properties expanding the potential of amaranth starch applications.