Three drying factors including pre-drying treatment (freezing), microwave-assisted drying (single-mode applicator-microwave vibro-fluidized bed [SMA-MVFB] and vibro-fluidized bed [VFB] drying) and drying temperatures (110-185C) were varied to investigate their effects on drying characteristics, energy consumption and instant rice quality. During drying cooked rice from 60 to 10% (wet basis), drying rate increased, whereas drying time decreased with the three drying factors. The highest drying rate of 0.554 g water/g dry matter·min and the shortest drying time of 2 min were obtained from SMA-MVFB drying of frozen cooked rice at 185C. This treatment also required the lowest energy of 0.204 kWh. However, in terms of product quality, unfrozen cooked rice subjected to VFB drying at 160C was superior as it was ranged in the whitest class, had the lowest bulk density and shrinkage values, and presented the best rehydration characteristic. After rehydration, it was whiter, bigger and softer than freshly cooked rice. PRACTICAL APPLICATIONSInstant rice has many advantages such as short preparation time, ease to carry and long shelf life. However, the existing products are not popular due to their poorer quality and higher price as compared with freshly cooked rice. As new food technology has continuously emerged, potential assessment of new technology for instant rice production would be imperative. Cooked rice is a difficult-to-handle material to be dried because of its sticky nature. So, a specific dryer is required to prevent agglomeration of cooked rice. Therefore, the effect of a new hybrid single-mode applicator-microwave vibro-fluidized bed (SMA-MVFB) drying on instant rice production and quality was investigated. In addition, a porous structure of instant rice is vital to ensuring its good rehydration capability and claimed to be improved by freezing before drying. Consequently, this study presented potential applications of SMA-MVFB drying and freezing pretreatment as well as drying temperature for preparing instant rice with good quality.

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