2008 CSBE International Meeting

1. 2008 CSBE International Meeting Microwave drying characteristics of two varieties of red lentils Opoku, A., L.G. Tabil and V. Meda Department of Agricultural and Bioresource Engineering University of Saskatchewan

2. Introduction • Lentils yearly export earnings $240 million (Canadian) • Lentils nutritious and healthy food, low in fat • Swath 1/3 of pod turns yellow or straight-cut fully mature • Threshed at 16 to 20% wb to reduce shattering losses • Needs drying to 12 -14% safe storage

3. Introduction • Conventional convective drying longer time and energy intensive • Microwave drying is energy efficient and faster heating in processing foods compared to convective drying • Microwave drying reduce retrogradation and has potential to increase the commercial use of lentil starch. • To better understand design, control and efficient operation of microwave drying systems for lentils, drying kinetics should be investigated.

4. Objectives • The objective of this study was to investigate the drying and color characteristics of red lentil varieties (Impact and Robin) using microwave drying system and to compare with convective drying.

5. Material • Robin lentils obtained from Pure T. Organics, Regina, SK • Impact lentils supplied by Reisner Seed Farm, Limerick, SK • Preconditioned moisture content Robin (9.85%) and Impact (6.50%) • Added water, rotated 5 h and stored at 5oC for a week • Conditioned moisture content Robin (20.82%) and Impact (21.86%)

6. Microwave drying • A combined microwave-convective dryer, Model NN-C980W (Panasonic Canada Ltd, Mississauga, ON) • Sample size of about 700 g • Microwave power levels P10 (713 W), P7 (606 W) and P4 (330 W) • Sample was removed and weighed at regular intervals • Cooled for 10 min and stored

7. Convective drying • A convective oven dryer ((Model 28, Precision Scientific Group, Chicago, IL)) was used • A sample size of about 700 g was placed on container • Two samples dried at the same time • Samples were removed and weighed at regular interval • The samples were dried at 70oC.

8. Color measurement • Hunterlab Color Analyzer (Hunter Associates Laboratory Inc., Reston, VA, U.S.A.) • Measured L, a, and b values before and after drying • Determined change in color, ΔL, Δa, and Δb • Total color difference ΔE

9. Data analysis - Drying models

10. Data analysis • TableCurve 2D (Jandel Scientific, San Rafael, CA) was used to determine the parameters of the models • Coefficient of determination (R2) and the standard error (SE) were determined for the models • Regression models were fitted to describe drying rate constant (k in min-1) and empirical constants n, a, and b • Equilibrium moisture content (EMC) was assumed to be zero for the microwave drying data and 3.80% dry basis (db) selected from Menkov (2000) • Drying rate determined as the amount of water removed per time (kg of water per kg of dry matter per hour)

11. Results - Microwave drying Effect of microwave power levels on lentils drying

12. Results – Microwave and convective drying rates

13. Results

14. Results – L, a, and b

15. Results – Color change

16. Conclusions • Times required to dry lentil samples were shorter compared to convective drying and decreased with increasing power levels. • Microwave drying resulted in higher drying rates compared to convective drying. • There was no difference in the drying rate between the two lentil varieties • Initial moisture content might have affected the drying time between the two varieties

17. Conclusions • Diffusion model provided a better fit for almost all the drying conditions, with higher R2 and lower SE compared to the other models. • Microwave and convective drying had more effect on the Impact variety than the Robin variety. • Convective drying of the Robin variety produced the lowest total color change. • The highest total color change was produced by convective drying of the Impact variety.

18. AcknowledgmentSaskatchewan Pulse GrowersNSERC Thank You