Solvent-free steam extraction of Citrus nobilis Peel essential oil: Chemical composition and bioactivity

The essential oil (EO) from Citrus nobilis Lour. peels was extracted using the Steam-Assisted Solvent-Free Extraction (SAFE) method, a process conducted without relying on organic solvent-based systems with reduced environmental impact. Volatile compounds were characterized through gas chromatographic separation coupled with mass spectrometric detection, which revealed d -limonene to be the predominant component of the EO. The EO exhibited strong antioxidant activity, as evaluated using the DPPH method with an IC 50 of 33.64 μg/mL. In addition, antibacterial effects against Staphylococcus aureus and Escherichia coli were evaluated by the disk diffusion assay, as evidenced by the distinct absence of microbial growth surrounding the disks of 12.12 mm and 8.13 mm, respectively. The minimum inhibitory concentration (MIC) values were 15.6 μL/mL for S. aureus and 31.2 μL/mL for E. coli . These results indicate that Citrus nobilis peel EO has potential, providing bioactive components from natural sources that may be utilized in biomedical and cosmetic formulations. Notably, this work provides a detailed evaluation of the application of the SAFE method, addressing aspects that have not been fully explored in previous studies for extracting EO from fresh Citrus nobilis peels cultivated in Gunung Omeh, Indonesia. The findings demonstrate that SAFE effectively preserves bioactive constituents while offering a sustainable strategy for citrus peel waste valorization with promising antioxidant and antibacterial applications.