Conventional drying. Microwave drying of rough rice. Rice = Big Business!! Drawbacks to conventional drying. Hypothesis

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1 Conventional drying Microwave drying of rough rice Deandrae Smith, Gbenga Olatunde and Griffiths Atungulu* University of Arkansas Division of Agriculture Department of Food Science Convective Heated air Natural Air In-bin Drawbacks to conventional drying Rice = Big Business!! Fissure formations as a result of: Temperature gradients Moisture Content gradients Causing reductions in: MRY HRY Also requires increased processing times. Perfect HRY: 70% ; Average HRY: 58% A 12% reduction in HRY = loss of approx. 90 million bu. of rice in the state of AR. Convective vs. Volumetric Heating Convective Heat slowly propagates from the surface towards the center of the rice kernel by conduction. Volumetric Heat is generated instantly and everywhere inside the rice kernel. Hypothesis Volumetric heating of rice during drying may: Reduce MC and temperature gradients Improve milling quality Result in one-pass drying of rough rice a. Conventional Heating at surface b. Volumetric Heating 1

2 Microwaves Past studies relevant to rice Authors Key findings MW type Study type Microwave ovens use radio waves at a specifically set frequency to agitate water molecules in food. As these water molecules get increasingly agitated they begin to vibrate at the atomic level and generate heat. Kirkpatrick, et al Park et al. (2012) Le et al. (2014) Atungulu et al. (2015) Microwave inactivate mold 2.45 GHz Batch Quality of brown rice dried using Convective and MW were comparable Heating duration affect HRY 2.45 GHz Batch 2.45 GHz Continuous Tempering stage is important 915 MHz Batch Preliminary studies Spring 2015 Natural Air Cooling Forced Air Cooling Studied the effects of MW heating of rice in conjunction with the following treatments: 1.Natural air cooling 2.Forced air cooling 3.Tempering followed by natural air cooling Tempering o C *Batch rice bed thickness at m. Specific vs. MC Preliminary Results Moisture Content (% w.b.) Specific (kj/kg-grain) 2

3 MW Drying strategy vs. HRY Conclusion Drying Strategy: MW + Temp + Natural Air Cooling ab ab ab ab bc ab ab ab a a ab ab ab ab ab c Power (kw) Time (min) Specific (kj/kg) MC Reduction (ppt) MC Final (%) HRY(%) HRY not significantly different from gently dried control samples. Control: Gently dried in EMC chamber d d Power (kw) Time (min) MC Reduction (ppt) MC Final (%) HRY(%) Potential merits of microwave drying Decreased MC and Temp gradients Improved Milling quality Improved HRY Continuous Drying Microbe Inactivation Aspergillus flavus Aflatoxin Very Carcinogenic Research objective 915 MHz Industrial Microwave Our objectives were to explore the feasibility of scaling-up MW drying: By testing continuous drying operations at varied rice bed thicknesess and MW energy intensity Evaluating impact of MW heating on rice drying rate, MRY and HRY Assess MW drying energy requirements 1. Transmitter 2. Wave Guide 3. Heating Zone 4. Conveyor Belt 5. Control Panel 3

4 Rice bed thickness m (inches) Experimental Design Power kw (BTU/h) Treatment time (min) Rough rice drying at 0.05 m bed thickness 0.01 (0.4) 3 (1364.8) 0.05 (2.0) 15 (6824.2) 0.01 (0.4) 4 (1819.8) 0.05 (2.0) 20 (9099.0) 0.01 (0.4) 5 (2274.7) 0.05 (2.0) 25 ( ) 8 ~ 450 (194) ~ 600 (260) 8 ~ 750 (320) 8 Rough rice drying at 0.01 m bed thickness Results Effect of microwave treatment on MC Final Bed thickness m (inches) Initial MC Final MC 450 (194) 0.01 (0.4) (2.0) (260) 0.01 (0.4) (2.0) (320) 0.01 (0.4) (2.0) * Power varied to compensate for reduced mass of grain in the heating oven with reduction in thickness; to ensure fixed specific energy (kj/kg) to the grain Effect of microwave treatment on MRY Bed thickness m (inches) MRY (%) Control A (0.38) 450 (194) 0.01 (0.4) A (0.30) 0.05 (2.0) A (0.37) 600 (260) 0.01 (0.4) A (0.75) 0.05 (2.0) A (3.02) 750 (320) 0.01 (0.4) B (0.93) 0.05 (2.0) N/A Number in parenthesis is the standard deviation Values with the same superscript (alphabets) are not significant (p >0.05) 4

5 Effect of microwave treatment on HRY Bed thickness m (inches) HRY(%) Control A (0.6) 450 (194) 0.01 (0.4) A (0.7) 0.05 (2.0) A 0.7) 600 (260) 0.01 (0.4) B (3.2) 0.05 (2.0) A (0.4) 750 (320) 0.01 (0.4) B (5.80) 0.05 (2.0) N/A Number in parenthesis is the standard deviation Values with the same superscript (alphabets) are not significant (p >0.05) Theoretical mass of H 2 O removed Final MC (% w.b.) Initial MC (% w. b) Mass of H 2 0 (kg) removed per kg of wet rice Theoretical Sample Size Lbs Kilograms Start Mois 24.00% End Moist 12.00% Water in Sample lbs Kilograms Dry Rice in Sample lbs Kilograms Water to Remove from Sample lbs Kilograms Ambient 60 Max Temp 205 Delta Rice BTU/Lb/Deg F 12,122.0 Heat 0.5 BTUs Water Heat 1 BTU/Lb/Deg F 7,656.0 BTUs Water Vapor 970 BTU/Lb/Deg F 29,100.0 BTUs 48,878.0 Total BTUs Electricity 3412 BTUs/KwH Kilowatt Hours Microwave Power Efficiency of conversion 80% Kilowatt Hours Electricity Theoretical kilowatt hours per Lb. wet per Kg wet per Lb.dry rice per Kg dry rice Efficiency factor 90% Practical Kilowatt hours per Lb. wet per Kg wet per Lb.dry rice per Kg dry rice Initial MC (% w. b) Final MC (% w.b.) Theoretical requirement, kwh to dry kg of wet rice Practical kwh = energy / practical efficiency Practical efficiency = efficiency of energy conversion (80%) efficiency factor (90%) Experimental vs. Theoretical energy requirements Specific kj/kg (BTU/lb) 450 (198) 600 (260) 750 (320) Bed Thickness m (inches) Initial MC Final MC Experimental kwh/kg wet rice rice 0.01 (0.4) (2.0) (0.4) (2.0) Theoretical kwh/kg wet 0.01 (0.4) (2.0) * Combined efficiency evaluated at 72% Specific energy kj/kg (BTU/lb) Bed Thickness m (inches) MW Drying costs Initial MC Final MC Experimental Cost ( /kg H20 removed) Theoretical Cost ( /kg H20 removed 450 (198) 0.01 (0.4) (2.0) (260) 0.01 (0.4) (2.0) 24% (320) 0.01 (0.4) (2.0) Based on a MW drying method using 600 kj/kg, the drying cost for 1 ton of rice is $8.44 5

6 Conclusion Study demonstrated feasibility of using continuous MW heating of rice to achieve one pass drying from harvest MC (24%) to near safe storage MC (~13%) The one pass treatment gave HRY comparable to control samples gently dried with natural air. Eg. Rice treated at 20 kw for 8 m gave final HRY of 67.43%. Theoretical and experimental energy utilization were comparable. Future studies Effect of milled rice functional properties Effect on sensory characteristics before and after cooking Implication on microbial load reduction Implication on parboiling and parboiled rice milling characteristics Implication of potential energy savings in parboiling. Dr. Griffiths G. Atungulu Acknowledgements Research Group Shantae Wilson Supriya Thote Gbenga Olatunde Zachary Young Anne Okeyo Benjamin Gainer Thank You!? Arkansas Rice Research and Promotion Board 6