Sustainable and green extraction of citrus peel essential oil using intermittent solvent-free microwave technology

In the present study, a novel technology called intermittent solvent-free microwave extraction (ISFME), which integrates intermittent microwave treatment with solvent-free extraction, was proposed. Taking Nanfeng citrus peel as the research object, the extraction efficiency and composition of its essential oil were evaluated and compared with conventional hydrodistillation (HD) and solvent-free microwave extraction (SFME). Results from single-factor experiments and response surface method optimization indicate that the optimal parameters for SFME are a power of 660 W, a duration of 20 min, and a water content of 60%, yielding an essential oil output of 3.47%. In contrast, the optimal parameters for ISFME, determined through single-factor experiments, are a moisture content of 50%, a power setting of 380 W, a reaction time of 6 min, a 15 min interval, and 4 reaction cycles, resulting in an essential oil yield of 3.51%. Notably, the extraction efficiencies of ISFME and SFME are significantly superior to that of HD, which requires 240 min and yields only 3.28% essential oil. Furthermore, ISFME demonstrates comparable performance to SFME in terms of reaction time, extraction rate, and oil quality, while operating at a substantially lower power requirement of 380 W compared to the 660 W needed for SFME. Additionally, the carbon dioxide emissions and energy consumption associated with ISFME are markedly lower than those of traditional methods, amounting to only one-third of the energy consumption of SFME. These findings underscore that ISFME not only enhances the efficiency and quality of essential oil extraction but also minimizes environmental impact, thereby highlighting its significant advantages in terms of sustainability and ecological responsibility.