The effect of combination dryer of hot air - infrared and microwave on some quality properties of parboiled rice

Drying is one of the most important stages in the rice milling process. In present study the effect of two drying techniques (intermittent and continuous drying) on the some quality properties of parboiled paddy (Fajr cultivar) were investigated. The intermittent drying was performed in two stages with a tempering time between drying steps using a combination dryer of hot air – infrared (HIR) at the first stage (from 35 to 23%) and microwave dryer at the second stage (from 23 to 13%). While drying technique of continuous was done using HIR dryer in one stage for moisture content reduction of paddy from 35 to 13% (w.b.). The experiments were carried out at drying temperature of 40, 50 and 60 oC, infrared radiation (IR) intensity of 0.32 and 0.49 w/cm2, microwave power of 100, 200 and 300 W and tempering duration of eight times previous drying (the first stage). After drying, quality properties (head rice yield (HRY), color and toughness force (TF)) of parboiled rice and drying time were measured. Results revealed that the effect of drying techniques, air temperature, IR intensity and microwave power on the quality properties of parboiled rice were significant (poC (200-0.32) and 40oC (100-0.32), respectively. But, the maximum drying time, color value and TF were obtained using continues drying method with 61.04 min, 19.63 and 227.3 N, respectively. In conclusion, the intermittent dryer technique is appropriate and recommendable method for parboiled paddy of Fajr variety.