Microwave irradiation to pretreat rosemary (Rosmarinus officinalis L.) for maintaining antioxidant content during storage and to extract essential oil simultaneously

An efficient microwave pretreatment (MP) method was employed to maintain quality of postharvest rosemary leaves. The influence of MP on the contents of carnosic acid (CA) and rosmarinic acid (RA) in rosemary leaves was investigated under four storage conditions (sunlight, shade, −20 °C, 55 °C). Rosemary leaves after MP (800 W, 15 min) had much lower degradation rates of CA and RA than those of non-treatment samples during the storage period. Moreover, retentions of CA and RA of pretreated leaves stored in the shade and −20 °C were higher than those of 55 °C and sunlight. In the pretreatment process, we simultaneously used microwave radiation to extract essential oil. No obvious differences were found in yield or composition between essential oils obtained by MP and hydrodistillation. Thus, MP could be a good method for extracting essential oil and maintaining quality in rosemary and other aromatic herbs.