Effects of different drying methods on drying time and some phytochemical traits of Solidago virgaurea L.

To investigate the effect of different drying methods on the Solidago virgaurea L., an experiment based on a completely randomized design with six treatments and three replications was conducted in 2018 in the Ecophysiology Laboratory of Shahid Beheshti University of Tehran. In this study, aerial parts of S. virgaurea L. was harvested from Sangdeh natural habitat located in Mazandan province at full flowering stage. The drying methods were shade and sun-drying (natural drying), oven-drying (40 and 50 °C), and microwave-drying (550 and 1000 watt). In all methods, drying of the plant materials was continued until the moisture content reached 10% (based on plant fresh weight). Methanolic extract was obtained from the dried samples and some secondary metabolites including content of total phenol, total flavonoid and leiocarposide were measured by Folin-Ciocalteu method, aluminum chloride method, and high-performance liquid chromatography (HPLC), respectively. The minimum (7 minutes) and maximum (60 hours) drying times were related to 1000 watt microwave drying and shade drying methods, respectively. The highest content of total phenol (30 mg Gallic acid /g DW) in shading drying treatment and the highest content of total flavonoids (7.95 mg Rutin/g DW) and leiocarposide (3.07 mg/g DW) was observed in the oven at 40 °C. In addition, active metabolites content decreased with increasing microwave power and oven temperature. In general, the correct choice of drying method depends on several factors, and among them, the type of active ingredient, optimal energy consumption and cost savings should also be considered.