Parboiled rice production without steaming by microwave-assisted hot air fluidized bed drying

Since the traditional parboiled rice process requires a high-pressure boiler and contains several processing steps, this work therefore proposes a new method of producing parboiled rice with no requirement of steam and fewer processing steps. With the proposed technique, a microwave-assisted hot air fluidized bed dryer (MWFB) was used. The Suphanburi 1 variety of paddy was first soaked in hot water and then dried by MWFB at temperatures of 111-169 degrees C and a fixed microwave power of 2 W/g wet paddy. The experimental results show that having the microwave turned on continuously for 180 s from the beginning of the drying process enhanced the rate of drying only when the drying rate was in the first falling rate period and could help to gelatinize the starch near the core of kernel, where it is very difficult to achieve gelatinization by hot air drying alone. During the MWFB drying process, the A-type crystalline structures decreased whilst V-type amylose-lipid complexes were formed. The amount of head rice yield, redness (a*-value), and yellowness (b*-value) increased whilst the lightness (L*-value) decreased during drying. To preserve the good head rice quality of the parboiled rice, the drying of the soaked paddy was not allowed to fall below 22-24% d.b. and the tempering step after drying was necessary. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.