Modeling of Starch Gelatinization Kinetics of Parboiled Aromatic Rice and Its Quality Using a Hot Air Fluidized Bed Dryer

In the modern dry heat parboiling process, the starch gelatinization and moisture content change simultaneously occur in the dryer. The information on starch gelatinization kinetics and quality of this process is primarily important for obtaining good-quality parboiled rice. The objective of this work was therefore to study the kinetics of starch gelatinization in a hot air fluidized bed dryer and quality of parboiled aromatic rice. The quality of parboiled rice, including head rice yield, texturral properties, color, and aroma compound (2-Acetyl-1-pyrroline), was quantitatively determined. Before the drying process, the KMDL 105 paddy was soaked in hot water at 75°C for 4 hours and dried at temperatures of 100, 120, and 130 °C with a bed height of 1 cm. The starch gelatinization was determined using differential scanning calorimetry. The experimental results show that the drying kinetics indicated that the reduction in moisture content during drying could be divided into two periods: the first falling and the second falling rate period. The effective diffusivity coefficient during the first falling rate period was higher than the second falling rate period. Degree of starch gelatinization increased as the drying temperature and time increase. The degree of starch gelatinization followed second-order kinetics, with the rate constant (k) changing with grain temperature and moisture content. The developed gelatinization kinetic model could well predict the experimental data, as indicated by RMSE given in the range of 4.65-6.50. Head rice yield and hardness of cooked parboiled rice increased with increasing degree of starch gelatinization. On the other hand, stickiness was decreased by 40%. After soaking, there was a 97% reduction in the quantity of 2-Acetyl-1-pyrroline. However, the quantity of 2-Acetyl-1-pyrroline did not cause further loss even though the samples were dried at high temperatures. The Maillard reaction at high temperatures during drying results in decreased brightness and a more yellowish-red tone in parboiled rice.