Methods of producing parboiled rice by hot air and combined microwave-hot air fluidized bed drying

Abstract

Conventional parboiled rice requires many components such as boiler, steam pipe and auxiliary devices. To reduce the complexity of the process, in this work, the new method of producing parboiled rice by hot air fluidized bed (HAFB) and microwave-hot air fluidized bed (MWHAFB) was proposed and investigated. In the experiment, the soaked paddy with an initial moisture content of 47 ± 1% d.b. and initial grain temperatures of 32–65 °C were dried at the drying air temperatures of 110–170 °C with microwave powers of 0.8–4.0 W/g_{wet paddy} (1.6–4.0 kW). The superficial air velocity at 4.6 m/s and bed depths of 5 cm (1 kg_{wet paddy}) and 10 cm (2 kg_{wet paddy}) were used. The experimental results showed that the drying time to reach an intermediate moisture content of 20 ± 2% d.b. was shorter with smaller bed depth, higher drying air temperature and higher microwave power. The MWHAFB and HAFB dryings could produce parboiled rice with a complete degree of starch gelatinization as the operating condition was suitable. The head rice quality of parboiled rice produced by MWHAFB and HAFB was not different. The parboiled rice had yellowish white for drying with excluding the tempering and had yellowish brown with including tempering as indicated by whiteness index (WI) with a value of 51–52. The consumption of energy was significantly lower in HAFB than that in the conventional process whilst the energy consumption between MWHAFB and conventional one was relatively comparable.

Keywords:

• Parboiled rice
• color
• fluidized bed
• head rice
• microwave

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was financial supported by The Office of The Higher Education Commission (OHEC) and Yala Rajabhat Universisty (YRU), Thailand. Also, the authors thanks to The Thailand Research Fund (TRF) for their financial support with Grant nos. DPG5980004 and RGU 6180004.