| Parboiling involves soaking, steaming, and drying, and is known to improve head rice yield (HRY), remove chalkiness, and retain nutrients. Because of an increasing number of rice cultivars developed, commingling of rice may happen during harvesting, distributing, or storage. Using commingled rice with a wide range of gelatinization temperatures (To) as a feedstock may cause inconsistent parboiled rice products. Therefore, this study was aimed at investigating the effect of soaking temperature and steaming duration on the quality of parboiled, commingled rice. Rough rice samples of individual or commingled rice cultivars with different To ranges were soaked at different temperatures (25, 60, 65, 70 or 75°C) for 3 h alone or in combination with steaming at 112°C for 10, 15 or 20 min; the milling and physicochemical properties of the resultant rice samples were characterized. Soaking at 25°C caused no morphological change, however soaking at temperatures above starch glass transition temperature but below To reduced chalkiness by facilitating a rearrangement of starch granules to form a more packed structure, thus increasing head rice yield. With increasing soaking temperature, head brown rice yield and To increased, whereas gelatinization temperature range and chalkiness reduced. During the soaking step, commingling or To difference had more influence on head brown rice yield than soaking temperature. However, when combined with the steaming step, soaking temperature was found to have more influence on the HRY of the resultant parboiled rice than commingling and steaming duration, whereas steaming duration had the greatest impact on yellowness, white core, deformed kernels and pasting viscosity. Commingled rice with a wide range of To tended to result in less desirable parboiled rice. It is recommended to select a soaking temperature close to To of commingled rice and a steaming duration to fully gelatinize starch without rendering excessive starch swelling in order to optimize the desirable quality characteristics of parboiled rice. |
