Abstract
The effect of urea and sodium chloride (NaCl) on the pasting properties and gelatinisation kinetic of corn starch was determined using rapid visco-analyser. Starch slurry (3 g in 25 g H2O) was heated at 3, 5, 7, 10, 15, and 20 degrees C/min. Peak viscosity, setback, and pasting temperature were recorded at all heating rates as well as the swelling power. The pasting temperature was used for activation energy (Ea) calculation according to the Kissinger plot and Ozawa model. The peak viscosity significantly (P <= 0.05) increased in presence of urea and NaCl at all heating rates compared to the control, while the setback dropped in NaCl and increased in urea. This indicates better amylose-amylose interaction prevention by NaCl. The pasting temperature exhibited higher values in NaCl and lower in urea. This signifies action of urea on the hydrogen bonding between starch molecules in the amorphous region of the granule (dominated by amylose). The protective action of NaCl is obvious on the high pasting temperature of corn starch. Kissinger and Ozawa kinetics equations exhibited similar Ea values for corn starch under the experimental conditions used in this work. Urea exhibited higher Ea compared to NaCl indicating ineffectiveness of urea to break hydrogen bonding at the conditions of the experiment.