Solvent-Free Microwave Extraction of Thymus mastichina Essential Oil: Influence on Their Chemical Composition and on the Antioxidant and Antimicrobial Activities

This article belongs to the Special Issue Antiradical, Chemopreventive and Antimicrobial Analysis of Bioactive Substances

Solvent-free microwave extraction (SFME) is a combination of microwave heating and dry distillation performed at atmospheric pressure without the addition of water or organic solvents that has been proposed as a green method for the extraction of essential oils from aromatic and medicinal herbs. In this work, SFME and the conventional techniques of steam distillation (SD) and hydrodistillation (HD) were compared with respect to the extraction and antioxidant and antimicrobial activities of Thymus mastichina essential oil. The main constituent of essential oils obtained using different methods was 1,8-cineole (eucalyptol). The results showed that the essential oils extracted by means of SFME in 30 min were quantitatively (yield) and qualitatively (aromatic profile) similar to those obtained using conventional HD over 120 min. In addition, SFME generates less waste and less solvent, consumes less energy, and provides a higher yield for a shorter extraction time, which is advantageous for the extraction of the T. mastichina essential oil compared to SD. The antioxidant and antimicrobial activities of the T. mastichina essential oil obtained from either SFME or conventional extraction methods (SD or HD) showed a similar pattern. Large-scale experiments using this SFME procedure showed a potential industrial application.

The authors acknowledge the Fundação para a Ciência e Tecnologia (FCT), Fundo Europeu de Desenvolvimento Regional (FEDER), and COMPETE 2020 for their financial support under theresearch project “The development of dermo-biotechnological applications using natural resourcesin the Beira and Serra da Estrela regions—DermoBio”, ref. SAICT-POL/23925/2016, presentedin the Notice for the Presentation of Applications No. 02/SAICT/2016—Scientific Research andTechnological Development Projects (IC & DT) in Co-Promotion (PDF) Solvent-Free Microwave Extraction of Thymus mastichina Essential Oil: Influence on Their Chemical Composition and on the Antioxidant and Antimicrobial Activities.