Essential oil content and components, antioxidant activity and total phenol content of rosemary (Rosmarinus officinalis L.) as affected by harvesting time and drying method

Background Preharvest and postharvest conditions of medicinal plants strongly affect the quantity and quality of their secondary metabolites. Here, the effect of different harvesting times (5 am, 12 noon and 5 pm) and different drying methods (shade at 25 °C, oven at 60 °C and microwave at 180 W) on essential oil content and components, total phenol content and antioxidant activity of rosemary was monitored. Results Harvesting time only had a significant effect on the essential oil content and components; however, all investigated traits were significantly affected by drying methods. The essential oil content of plants harvested at 5 am and 5 pm was higher than those harvested at 12 noon. The highest amount of essential oil was obtained from shade (0.85–1.12%) and oven (0.66–1.04%) dried plants, respectively. Total phenol and antioxidant activity of oven dried plants were significantly lower than shade and microwave-dried plants. The number, type and amount of essential oil components were affected by harvesting time and drying method. α-Pinene, verbenone and camphor were the major components of the essential oils. Oxygenated monoterpenes were the main group of essential oil compounds in all treatments. The results of biplot and cluster analysis, based on the measured traits, placed the treatments in three separate clusters; I: shade dried, II: oven-dried, and III: microwave-dried plants. Conclusion Generally, to obtain the higher essential oil content, phenol and antioxidant activity, harvesting at 5 am and 5 pm and also shade drying are recommended; however, for reaching to essential oil with specific quality, different harvesting time and drying method could be used.