Morphological, functional and pasting properties of starches separated from rice cultivars grown in Nigeria

This study was carried out to determine the composition, morphology, functional and pasting properties of rice starches isolated from different rice cultivars (IGR, EAR, ILR and N2R). The starches were isolated from their flours by using a modified deproteination method in 0.1% NaOH. The highest starch yield of 65.00% was obtained from EAR with a residual protein of 0.41% and the lowest starch yield of 45.70% from IGR with a residual protein of 0.42%. The apparent amylose (AAM) content of rice starches ranged from 21.88 to 26.04%. Rice starches contain 10.40-12.77%, 0.10-0.70% and 0.20-0.24% moisture, fat and ash contents, respectively. The sizes of the starch granules obtained from SEM were between 3-8 μm. Some of the granules were individual (single) while others were fused (compound granules). The rice starch granules were polygonal and angular-shaped. When heated from 55 to 95°C at 10°C intervals, starches with higher amylopectin content had higher swelling power (SP). Both SP and water solubility index increased with increased temperature. The bulk density, dispersibility and pH of the rice starches ranged from 0.41-0.56 g/ml, 75.10-82.12% and 5.3-6.9, respectively. Pasting parameters were evaluated using RVA. Significant differences were observed in individual pasting parameters of the rice starches especially in peak viscosity, trough viscosity, final viscosity and setback viscosity. The results revealed that cultivar difference has an effect on composition and pasting properties of rice starch.