Abstract
A scaled-up process for paddy drying was developed using hot air (HA) combined with radio frequency (RF) heating. The study was conducted using hot air (control treatment) arranged in descending order in four temperature levels, namely 80 °C at moisture content of 25–26%, 70 °C at moisture content of 20–25%, 60 °C at moisture content of 17–20%, and 50 °C at moisture content of 13–17%, as well as with hot air combined with radio frequency (HA/RF) at different paddy temperatures (45–60 °C) by adjusting the appropriate RF energy when passing through RF heating chamber, namely HA/RF45, HA/RF50, HA/RF55, and HA/RF60. Each treatment was performed in three replicates and data were statistically analyzed in a randomized complete block design. The quality attributes of paddies affected by the drying process were assessed: fissure percentage, color, milling quality, and sensory evaluation. The drying efficiency showed that the drying time and the specific energy consumption could be decreased by up to 54.44% and 23.17% at HA/RF60 and HA/RF45, respectively. As the RF heating temperature increased, the fissure percentage of brown rice kernels at HA/RF45 and HA was not significantly impacted. Regarding color evaluation, combining RF heating and convective drying at all given conditions could be statistically applied in terms of the b*, WI, and ΔE* value. Considering the milling yield of HA as the baseline, head rice yield was maximized at HA/RF45, while bran yield reached the maximum at HA/RF60. The liking score of cooked rice after it was dried using the HA method was the highest. This study concludes that the HA/RF45 was the most appropriate drying condition, and this may provide preliminary exposure to the industrial drying of paddies.
Highlights
IntroductionRice production plays an important role in Thailand’s economy, with approximately
Rice production plays an important role in Thailand’s economy, with approximately30 million tons of paddy production harvested per year
The effects of the four different radio frequency (RF) heating temperature levels combined with the hot air drying process were compared to convective hot air drying
Summary
Rice production plays an important role in Thailand’s economy, with approximately. 30 million tons of paddy production harvested per year. The optimum harvest period for the paddy rice variety Hom Mali is 25–35 days after heading at a moisture content level of 18–28% (w.b.) when harvested by a combine harvester [1]. The most commonly used mechanical drying systems in Thailand are the continuous flow dryer and re-circulating batch dryer. There are around 2000 industrial-scale rice mills across the country. The continuous-flow hot air dryer is the most selected method for use at industrial-scale rice mills because of its cost and drying rate. A paddy is dried by hot air (HA) (40–80 ◦ C)
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