Rheology and functional properties of starches isolated from five improved rice varieties from West Africa

Starches were isolated from five improved rice varieties developed by West African Rice Development Agency (WARDA) namely FARO 32, FARO 51, FARO 52, FARO 54 and NERICA. Starch yield and amylose content varied between 73.77-70.02% and 22.88-24.48% respectively. Starches were polyhedral in appearances and within the size range 1.5-6.1 mu m. The X-ray diffraction patterns of the starches show a peak centered on 2 theta = 5.1 degrees, a doublet on 17.1 degrees and 18.1 degrees, and another single peak at 23.12 degrees. However, NERICA shows no doublet but a single peak at 2 theta = 17.1 degrees with a small shoulder. The peak viscosity of the starches ranged between 147.48 and 209.17 RVA corresponding to FARO 52 and NERICA respectively. A neat distinction is observed between the marked shear thinning of FARO 52 and the apparently plastic behavior of the other samples. Important differences appear in the low shear region where the viscosity increases in the following order: FARO 52 < FARO 54 < FARO 51 < FARO 32 < NERICA. The mechanical spectra exhibit similar profiles as the storage modulus (G') prevails over the viscous component (G '') and is weakly dependent on the frequency. However, the storage modulus increases in the same order observed for low shear viscosity. The percentage retrogradation was between 61.9 and 86.6% and NERICA starch showed the least retrogradation indication. NERICA starch exhibited highest swelling and solubility, while the least was observed in FARO 52. Rheology and functional properties are dependent of amylose composition. This study provides knowledge for the utilization of starches isolated from improved rice varieties that would be relevant for both domestic and industrial applications. (C) 2011 Elsevier Ltd. All rights reserved.