Studies on the hydrothermal modifications of new cocoyam (Xanthosoma sagittifolium) starch

Native new cocoyam starch (nNCS) was subjected to annealing (aNCS) and heat moisture treatment at 18% moisture level (h18NCS), 21% moisture level (h21NCS), 24% moisture level (h24NCS) and 27% moisture level (h27NCS) as hydrothermal treatments. Scanning electron and light microscopy revealed round and polygonal shapes with sizes ranging from 15 to 40 microm for native and modified starches. nNCS showed "A" pattern X-ray diffraction and no significant differences were observed in the X-ray pattern of the modified starches. Swelling power and solubility reduced following heat moisture treatment. At all pH studied (2-12), unmodified new cocoyam starch exhibited higher swelling capacity and solubility than the modified derivatives. Hydrothermal modifications improved water absorption capacity but reduced oil absorption capacity. Pasting temperature of native starch shifted to higher values following annealing and heat moisture treatment. Hot paste viscosity (Hv), viscosity after 30 min holding at 95 degrees C (Hv30) and cold paste viscosity (Cv) reduced after annealing and heat moisture treatment. The result also indicates that hydrothermal treatments reduced the tendency for setback. As the number of days of storage of starch paste increased from 1 to 10, light transmittance of all the starches reduced but marked reduction of light transmittance was observed in native starch. DSC studies revealed increase in gelatinization temperature following annealing and heat moisture treatment. Starch hydrothermal modifications reduced retrogradation as enthalpies of regelatinization reduced following modifications. The regelatinization peak in the second day scanning shifted to lower temperature than the gelatinization peak in first run heating DSC curve for all samples. The regelatinization peak also became larger and shifted to higher temperature range when the storage days increased from 2 to 7.