Optimization of solvent-free microwave extraction of essential oil from the fresh peel of Citrus medica L. var. arcodactylis Swingle by response surface methodology, chemical composition and activity characterization

Citrus medica L. var. sarcodactylis Swingle (finger citron) is a traditional Chinese herb and considered as a functional vegetable. In this study, a green extraction method of solvent-free microwave (SFME) was used to isolate finger citron essential oil (FEO). Under the optimal extraction process parameters, the FEO yield (1.65% +/- 0.05%) from SFME was 27.91% higher than that from hydro distillation (HD) (1.29% +/- 0.03%), and its total phenolic and total flavonoid content were higher than that HD. The GC-MS results further showed the contents of some active components in FEO from SFME method increased significantly, including Citronellol (+4.8%), Geraniol (+3.95%), trans-Citral (+3.92%), cis-Citral (+2.06%), alpha-Terpineol (+1.09%), Hexadecanoic acid (+1.02%) and Linoleic acid (+0.9%). The antibacterial activities of FEOs were comprehensively evaluated by 6axe cobweb charts. The experimental results of antioxidant, acetylcholinesterase inhibitory and antimicrobial activity showed that FEO from SFME method were significantly better than that from HD method. No solvents were used in the extraction of essential oils by the SFME method, which was in full compliance with the current requirements of green chemistry. This research will provide a new process for the extraction of essential oil from the fresh peel of finger citron and contribute to its industry development.

Automated summary

In this study, a solvent-free microwave extraction method (SFME) was used to isolate finger citron essential oil (FEO) with higher yields and better quality compared to hydro distillation (HD). The GC-MS results showed that the SFME method significantly increased the contents of some active components in FEO. The FEO from SFME method exhibited better antioxidant, acetylcholinesterase inhibitory, and antimicrobial activities.