Extraction, synthesis, characterization and antioxidant properties of oxidized starch from an abundant source in Nigeria
Starch is a renewable and environmentally compatible polymer but due to some inherent drawbacks like its hydrophilic character, poor mechanical properties, and its inability to withstand processing conditions such as extreme temperatures, diverse pH, starch in its native form cannot be applied satisfactorily in industrial operations. Modification of starch however, enhances its applicability in both food and pharmaceutical industries. In this study, Manihot esculentus (M. esculentus) starch was modified chemically by oxidation. Foam capacity and emulsion capacity of the native and oxidized M. esculentus starch was determined. Fourier Transmittance Infra- Red (FTIR) and Raman spectroscopies was used to confirm starch modification while characterization was done using Scanning Electron Microscopy (SEM) and X- Ray Diffraction (XRD). Antioxidant activity of the oxidized M. esculentus starch was assessed using DPPH (2, 2-diphenyl-1-picrylhydrazyl-hydrate) free radical assay. Our results show that modification had no significant effect on the foam and emulsion capacities. FTIR results revealed a new band at 3007 and 3283 cm-1 while SEM showed that oxidation did not alter the predominantly circular-shaped starch granules. The XRD patterns of both native and modified were found to be similar. Differential Scanning Calorimetry returned two new endothermic peaks in the oxidized M. esculentus starch with an improved gelation capacity and increased enthalpy of gelatinization. The IC50 of the oxidized starch was notably higher than that of the reference standard, ascorbic acid.
Keywords: M. esculentus, starch, oxidation, antioxidant activity, DPPH.