Chemical Composition, Allelopathic Potential, and Antimicrobial and Anticholinesterase Activity of Citrus sinensis (L.) Peel Oil

Abstract

Citrus sinensis is renowned for its notable biological effects. This research aimed to characterize the chemical composition of oil derived from the peel of Citrus sinensis (L.), referred to as CsPO, and to assess its antimicrobial efficacy against strains of Enterococcus faecalis (ATCC29212), Escherichia coli (ATCC25922), Candida albicans (ATCC10231), and Mycobacterium smegmatis (ATCC14468). Additionally, the investigation sought to analyze its impact on the growth of butter bean (Phaseolus lunatus) radicles, evaluate its inhibitory effects on acetylcholinesterase enzyme (AChE) both in vitro and in silico through molecular docking simulations, and determine its potential phytotoxicity. The analysis of the CsPO composition using gas chromatography coupled with mass spectrometry (GC-MS) identified thirty-three (33) monoterpene and sesquiterpene compounds, e.g., β-citronelene (7.33%), β-pinene (9.63%), car-3-en-2-one (8.43%), eugenol (4.24%), limonene-10-ol (8.26%), α-humulene (10.52%), α-neo-clovene (4.83%), and β-acoradiene (12.47%). CsPO demonstrated varying levels of antimicrobial activity, ranging from low (+) to moderate (++). In the allelopathy assay, one of the treatments exhibited alterations in radicular growth and germination rate of butter bean seeds. The in vitro anticholinesterase assay revealed an inhibitory concentration (IC50) of 72 µg/mL. These findings were corroborated by the in silico anticholinesterase assay, highlighting the potential of β-citronelene, limonene, β-acoradiene, and α-humulene to inhibit acetylcholinesterase. The in silico assay yielded binding energy values between -6.2 and -9.6 kcal/mol, closely resembling those of the galantamine inhibitor (-9.8 kcal/mol, RMSD 0.3678 Å). This study underscores the significant inhibitory activity of CsPO against AChE, suggesting its potential use in treating conditions like Alzheimer’s disease and other relevant ailments. Furthermore, this study aims to enhance the scientific understanding of this essential oil, thus contributing to its potential applications in agriculture and medicine.