Optimization of Different Drying Systems for Lavender Leaves Applying Response Surface Methodology

Lavender leaves, widely used as flavors for foods and beverages, are a rich source of phenol components and antioxidant. Drying method is of vital importance for keeping these compounds. In this study, lavender leaves were dried by means of Atmospheric Freeze (AF), Multi-Stage Semi-Industrial Continuous (MSSIC), and Near Infrared-Vacuum (NIR-Vacuum) dryers and optimized by Response Surface Methodology (RSM) for the highest drying rate, total phenol content, antioxidant capacity, and the lowest color indicators change. Lavender leaves were also dried under natural conditions as the traditional method. Multi-stage drying caused tempering phenomenon and, consequently, drying rate increased obviously. Near infrared-vacuum dryer had suitable performance on keeping the active ingredients of lavender leaves. Optimum point to dry lavender leaves in atmospheric freeze dryer was found to be -5℃. The optimum temperature points in the multi-stage semi-industrial continuous dryer were achieved to be 60, 40, and 60℃ for the first, second, and third stages, respectively. The optimum point in near infrared-vacuum dryer was 60℃ and 20 kPa for air temperature and pressure, respectively. Based on the results, among several drying methods, near infrared-vacuum dryer was the more suitable for drying lavender leaves.