Composition of rosemary essential oil (Rosmarinus officinalis) as affected by drying method

The influence of the drying method on volatile compounds of Rosmarinus officinalis was evaluated. The drying methods tested were convective (CD) and vacuum-microwave (VMD), as well as a combination of convective pre-drying and VM finish-drying (CPD–VMFD). Rosemary drying kinetics was described by a simple exponential model for CD and VMD, while VMFD kinetics consisted of two periods: linear until a critical point and exponential beyond that point. Volatile compounds of rosemary samples were extracted by steam-hydrodistillation and analyzed by GC–MS. Thirty-four compounds were tentatively identified, with α-pinene, bornyl acetate, camphene and 1,8-cineole being the major components. The total volatiles concentration of fresh rosemary (135 g kg⁻¹) decreased considerably during both CD (87.2 g kg⁻¹) and VMD (61.9 g kg⁻¹). CPD–VMFD was the best option for drying rosemary because the time required was relatively short (30 min), and the aroma quality was good according to both instrumental (100 g kg⁻¹) and sensory analyses.