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One-pass drying of rough rice with 915 mHz industrial microwave vs. degree of milling and milled rice quality G. ATUNGULU (1), G. Olatunde (2) (1) University of Arkansas, , U.S.A.; (2) University of Arkansas Division of Agriculture, , U.S.A..
Industrial milling practice for rough rice targets a degree of milling that results to milled rice surface lipid content (SLC) of 0.4% for optimal head rice yield (HRY) recovery and better storability. Equipment settings to achieve the said SLC is based on characteristics of rice dried using convective heated air or natural air drying operations which are typically performed in multiple passes of air. Volumetric heating which is associated with microwave (MW) drying could prevent intra-kernel moisture content and temperature gradients, which is likely to impact mechanical properties of the rice and may have an impact on the rice milling behavior. This study is the first to investigate, one-pass drying of rough rice with 915 mHz industrial MW and to report on implications of the process versus rice milling degree and milled rice quality characteristics. Medium grain rough rice (24% MC) at bed thicknesses of 0.01 and 0.05 m was dried in a one-pass, continuous drying operation for 8 minutes using pilot scale MW set at specific energy of 450, 600 and 750 kJ/kg. Samples from each treatment were milled for durations of 0, 15, 30, 45 and 60 s. The result shows that, as milling duration increased, surface lipid content (SLC) reduced by an average of 80%. Sample dried at 0.01 m bed thickness generally reached a SLC >0.32% in shorter milling durations (30 s) compared to at 0.05 m bed thickness which averaged 0.65% SLC in the same duration. Marginal reduction in protein content was observed with increase in milling duration (p <0.05). As the milling duration increased from 0 to 60 s, HRY and MRY reduced (p<0.05). The highest value of 77% HRY was obtained at 450 kJ/kg and 0.01 m bed thickness while the lowest value of 13% HRY was obtained at 750 kJ/kg and 0.05 m bed thickness. In general, HRY and MRY obtained after 30 s of milling were <60% and <70%, respectively. View Presentation |
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