Essential oil from Thomson Novel sweet orange peel waste functions as a green disinfectant inspired by traditional medicine

Citrus peel waste is no longer considered “waste”, but rather as a rich source of bioactive substances with high added value for the development of “green label” products. Citrus sinensis (L.) Osbeck (sweet orange) is one of the most popular fruits worldwide, whose peel is used in the traditional medicine of nations to relieve indigestion and flatulence, as an expectorant and antitussive, and to treat skin infections and as a disinfectant. Accordingly, the present study was designed to identify the chemical constituents and evaluate the inhibitory activity of the essential oil of C. sinensis cv. Thomson Novel peel against 11 strains of opportunistic microorganisms in Iran. Fresh orange fruits of this variety were purchased from the market, and the outer layer of the peel was carefully separated from the fleshy part and dried in the shade. Extraction of C. sinensis peel essential oil was performed using a Clevenger-type distillation system, and qualitative analysis of the essential oil was performed using a gas chromatography-mass spectrometer (GC-MS) system. To evaluate the inhibitory potential of the essential oil, after initial screening by agar well diffusion technique (ZOI), the minimum inhibitory concentration (MIC) and minimum bactericidal/fungicidal concentration (MBC/MFC) were determined by the standard micro-dilution method. Based on the chromatogram output from the GC-MS device, the essential oil of C. sinensis peel contained 15 different compounds, of which monoterpene hydrocarbons had the highest amount with 75.27% in the total chemical profile. The results showed that D-limonene, with 71.36% was the first dominant compound of this essential oil. Initial screening showed that the essential oil of C. sinensis peel had visible inhibitory activity only on Staphylococcus aureus with a ZOI of 9.5 ± 2.12 mm. The lowest MIC and MBC values of the essential oil of C. sinensis peel were against the Gram-negative Acinetobacter baumannii (MIC = 62.5 µg/mL and MBC = 500 µg/Ml), which was significantly weaker than rifampin. Therefore, the essential oil of C. sinensis cv. Thomson peel Navel exhibits bacteriostatic potential against specific strains, warranting further investigations for its potential application in natural preservation or supportive disinfectant formulations.