2008 CSBE International Meeting

1. 2008 CSBE International Meeting Microwave-vacuum drying and quality characteristics of sour cherries Opoku, A., V. Meda and L.G. Tabil Department of Agricultural and Bioresource Engineering University of Saskatchewan

2. Introduction • Sour cherry provides a good source of fiber, vitamins A and C, high amounts of anthocyanins and low in fat • Healthy food choice for prevention of heart disease, diabetes, and obesity • Seasonal crop Saskatchewan frozen storage or dry to maintain quality, nutritional value and longer shelf-life • Several hours needed to dry using convective hot-air dryer

3. Introduction • Microwave-vacuum drying (MVD) • Rapid and efficient energy usage • Yields dried products with excellent quality • Drawback is non-uniform heating • Drying behavior is necessary for equipment design and optimal drying • Microwave-vacuum drying kinetics and quality characteristics of sour cherry need to be studied

4. Objectives • The objective of this study was to investigate The objective of this study was to investigate the drying and quality characteristics of cherries using a microwave-vacuum dryer

5. Material • Frozen, pitted sour cherries obtained from Riverbend Plantation Gourmet Foods (Saskatoon, SK, Canada) • Thawed at 5oC for more than 24 h • Juice drained and thawed cherry stored at 5oC • The initial moisture content of the cherries was about 83.44% wb

6. Microwave and Microwave-vacuum drying • A combined microwave-vacuum dryer, Model VMD 1.8 (ENWAVE Corp., Vancouver, BC) • Sample size of about 150 g • Microwave power levels P10 (404 W), P8 (344 W) and P6 (300 W) • Two vacuum pressure levels V20 (67.0 kPa) and V10 (33.5 kPa) • Sample was removed and weighed at regular intervals • Dried to 40 to 45%, cooled and stored

7. 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

8. Methods – Water activity • Measured using Pawkit water activity meter (Decagon Devices, Inc., Pullman, WA, U.S.A.) • Accurate to +0.02 aw • Two replicates were made for each sample • 3 readings for each replicate

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, b, and c • Equilibrium moisture content (EMC) was assumed to be zero for the microwave-vacuum drying data

11. Results – Microwave-vacuum drying Effect of microwave power and vacuum levels on sour cherry drying

12. Results

13. Results – L, a, and b color values

14. Results – Color change

15. Results – Water activity

16. Conclusions • The vacuum pressure levels did not greatly influence the drying time of the sour cherries compared to the microwave power levels • Increasing the microwave power level produced faster drying times for the samples. • The polynomial and exponential models were fitted to the drying data

17. Conclusions • Vacuum pressure and the microwave power levels significantly influenced the final quality of the dried cherries. • Total color difference was dependent on microwave power and vacuum pressure levels. • The lowest total color change was produced at power level P4 and vacuum pressure of 33.5 kPa. The total color difference was highest at power level P10 and vacuum pressure of 67.0 kPa • Water activity of the samples after drying ranged from 0.78 to 0.82 for moisture content range of 39.31 to 45.50% wb.

18. Thank You