Antibacterial and antioxidant activity of compounds from Citrus sinensis peels and in silico molecular docking study

Abstract

The increasing prevalence of drug resistance, adverse side effects of existing antibiotics, and the resurgence of previously known infections have necessitated the search for new, safe, and effective antimicrobial agents. The peels of Citrus sinensis (300 g) were extracted using maceration and ultrasonic-assisted extraction methods with ethanol, resulting in yields of 20.99 g and 11.5 g (7%, 7.5%), respectively. Silica gel column chromatographic separation of the ethanol extract yielded N-(1,3,4,5-tetrahydroxydecan-2-y1)octanamide (1), decanoic acid (2), β-sitosterol-3-O-β-D-glucopyranoside derivative (3), and (z)-ethyl tetradec-7-enoate (4). GC-MS analysis of the essential oil detected 7 chemical components accounting for 99.84% of the total composition of which limonene was found to be the predominant constituent (87.5%). In vitro antibacterial tests revealed promising zones of inhibition by ethanol extract (12.67±0.58 mm, at 150 mg/mL), compound 4 (15.67±2.88 mm, at 6 mg/mL), and compound 1 (12.00±0.00 mm, at 6 mg/mL) against E. faecalis, S. typhimurium, and P. aeruginosa, respectively, compared to gentamicin (13.00±1.73 mm, 18.00±1.00 mm, and 16.67±1.15 mm, respectively at 10 µg/mL). DPPH radical scavenging activity indicated that compound 1 exhibited an IC50 value of 0.05 mg/mL, compared to ascorbic acid's 0.016 mg/mL. In silico molecular docking studies revealed that compounds 1 and 3 had the lowest scoring poses against E. coli DNA gyrase B enzyme, human peroxiredoxin 5, and S. aureus pyruvate kinase, respectively. These findings support traditional applications of Citrus peels in treating infectious diseases, particularly against Gram-positive strains, and highlight their potential use as antibacterial ingredients in cosmetics.