Effect of Turntable Rotation Rate on Drying Kinetics and Functional Properties of Lemon Peel during Microwave Drying

Abstract

In this study, the effect of the rotational rate of turntable on drying kinetics of lemon peels and some functional and flow properties of lemon peel powders were investigated. Lemon peels were dried by microwave drying using different rates of rotation (0, 6.5, 9.5, and 12.5 rpm) at different microwave power levels (180W, 300W, 450W and 600W), and dried by oven drying and freeze-drying methods. Drying time was shortened by 72-95% by microwave drying compared to oven drying. Microwave drying with rotation provided 5.6-23.8% reduction in drying time of peels compared to drying without rotation. Effect of rotation rate on drying time of lemon peels depended on the microwave power level. 9.5 rpm caused lower initial drying rates compared to 6.5 and 12.5 rpm during microwave drying except 600W power level. Page model provided lower SSE, RMSE, and higher R2 values within 5 different thin layer models. The Deff value, ranging between 1.7 x 10-8 m2s-1 - 7.6 x 10-8 m2s-1, was higher during microwave drying with rotation. The activation energy ranged between 21.3-22.7 W/g. Microwave drying provided higher bulk density, similar or lower water holding capacity and oil retention capacity values compared to freeze drying and oven drying. Freeze dried lemon peel powder had the lowest bulk density due to its porous structure. Microwave drying without rotation and the highest power level caused lower bulk density. At higher power levels, influence of turntable rotation on WHC was more notable.