Physicochemical properties of pregelatinized and microwave radiated white and red cocoyam (Colocasia esculenta) starches

Abstract

The need to explore potentials of pregelatinization and microwave radiation as non laborious and inexpensive processes of starch modification and to promote utilization of cocoyam starch were the reasons behind this study. Starches extracted from white and red varieties of cocoyam were modified using two physical methods: pregelatinization and microwave radiation. Functional and pasting properties of native and modified starches were evaluated using standard methods. Swelling power of the starches (1.70 – 4.10) reduced significantly (p<0.05) with pregelatinization but increased significantly (p<0.05) with microwave radiation. Water absorption capacity (1.00 – 3.20 ml/g), packed bulk density (0.56 – 0.83 g/ml) and loose bulk density (0.46 – 0.64 g/ml) of the starches increased significantly (p<0.05) while least gelation concentration (4.00 - 8.00%) reduced significantly (p<0.05) as a result of modifications. Peak, trough, breakdown, final and setback viscosity of white and red cocoyam native starches were 3687 cP and 4144 cP; 2213 cP and 2519 cP; 1474 cP and 1625 cP; 3595 cP and 4142 cP; 1382 cP and 1623cP respectively. Pregelatinization significantly increased (p<0.05) these pasting viscosity values in white cocoyam starch but reduced them significantly (p<0.05) in red cocoyam starch. Microwave radiation caused a significant increase (p<0.05) in the pasting viscosity values of both white and red cocoyam starches except breakdown viscosity which reduced.