Effect of the drying process on the physical properties and cooking quality of japonica aromatic rice

aromatic rice

Japan Society for Food Engineering

Japan Journal of Food Engineering

Rice is a major economic crop in Japan, where it is usually dried using a batch-type dryer until the final moisture content (FMC) reaches below 9%. The influence of low FMC (about 9%) produced by four drying temperatures (30, 40, 50, and 60℃) on the physical properties, milling, and cooking qualities of short grain aromatic rice were investigated. The obtained data were also compared with standard FMC (about 12%) treatments which were dried in a batch type dryer. The experimental result showed that for low FMC samples, head rice yield (HRY) was increased by 4% at drying temperatures of 30℃ and 40℃ but was reduced by about 20% at 60℃ in comparison with control samples (25℃, 60% RH). The water uptake ratio (WUR) and volume expansion ratio (VER) were decreased significantly as the drying temperatures were increased. We can conclude that low FMC (9%) could produce higher HRY, if the drying temperature is 40℃ or less. In addition, high drying temperatures (50℃ and 60℃) caused increases in the number of fissured kernels, energy consumption and decreases in HRY, WUR, and VER. Maintaining the HRY and keeping a cooking quality at maximum level are the main task for the optimization of drying process. It was occurred at drying temperature less than 40℃ with a low FMC for aromatic rice. Therefore, a drying temperature of more than 40℃ would result in deterioration of quality of japonica type aromatic rice, followed by low FMC.