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Drying rate control in the middle stage of microwave drying |
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| Authors: | Zhenfeng Li,G.S.V. RaghavanNing Wang,Clé ment Vigneault |
| Affiliation: | a College of Mechanical and Electronic Engineering, Northwest A&F University, Yangling, Shaanxi 712100, China b Department of Bioresource Engineering, McGill University, 21111 Lakeshore Road, Ste-Anne-de-Bellevue, QC, Canada H9X 3V9 c Biosystems and Agricultural Engineering, Division of Agricultural Sciences and Natural Resources, Oklahoma State University, 111 Ag Hall, Stillwater, OK 74078, USA d Horticulture Research and Development Center, Agriculture and Agri-food Canada, 430 Gouin Blvd., Saint-Jean-sur-Richelieu, QC, Canada J3B 3E6 |
| Abstract: | Microwave drying of apples at constant temperatures follows typical drying curves. The middle stage of the drying process shows a faster drying rate and accelerated moisture evaporation. Meanwhile, more flavors are lost, surface color is degraded, and charring often occurs in this stage. To improve the drying effects, drying curves were controlled and changed in this study. The drying curve was linearized by automatically varying drying temperatures in the middle stages. The controlled drying process therefore led to an optimized temperature profile. To simplify the drying methods, apples were further dried with the obtained temperature profile, while drying curves were online monitored but not controlled. It was proved that slowing down the drying rate in the middle stage could improve the product quality in terms of color, flavor, and overall appearance, while the drying time and energy consumption were still acceptable (within 200 min and 22 kJ/g, respectively). |
| Keywords: | Microwave drying Drying curve Drying rate control Apple |
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