Optimization of instant jasmine rice process and its physicochemical properties

Instant, or quick-cooking, rice is becoming more popular nowadays. However, it still poses problems with respect to rehydration time and quality. This study investigated the effects of processing factors: moisture content, pressure and drying temperature on physical and physicochemical properties of instant rice and its eating quality using response surface methodology (RSM). Hardness, chewiness and the whiteness index (WI) were used as responses due to their high R2 (0.927, 0.633 and 0.836, respectively) and lack-of-fit. The hardness and chewiness of rice decreased as moisture content and pressure increased. Higher drying temperatures caused increases in hardness and chewiness. Only pressure and moisture content affected density, rehydration ratio, and increase in the volume of instant rice, which was due to the porosity of the kernels. Rehydration ratio had a negative correlation with density (r = −0.886) but a positive correlation with volume increase (r = 0.637). Pressure was the main factor influencing the pasting properties of instant rice. All pasting properties of instant rice were far lower than those of milled rice, but instant rice had higher cold paste viscosity, which is typical of pregelatinized flour. This indicated rapid water absorption and shorter cooking time. Instant rice processing also caused development of amylose–lipid complexes observed as the V-type pattern in an X-ray diffractometer.