Chemical analysis and effectiveness of essential oils extracted from Citrus sinensis and Citrus tangerina as antioxidants, antibacterial and antileishmanial agents

Citrus peel waste represents an abundant and low-cost source of bioactive essential oils. This study aimed to provide an integrative characterisation of the peel essential oils of sweet orange ( Citrus sinensis ) and tangerine ( Citrus tangerina ), evaluating their chemical composition, antioxidant, antibacterial, and antileishmanial properties, and discussing their potential industrial applications. Essential oils were extracted by hydrodistillation and analysed by GC–MS. Antioxidant activity was assessed using DPPH and FRAP assays. Antibacterial activity was determined by the broth microdilution method against eleven bacterial strains. Antileishmanial activity was evaluated against Leishmania tropica promastigotes using the MTT assay. Both oils were overwhelmingly dominated by dl-limonene (97.8% in C. sinensis ; 97.2% in C. tangerina ). C. sinensis oil exhibited significantly stronger antioxidant activity (DPPH IC₅₀ = 18.5 mg/mL; FRAP = 87.3 µM TE/g) than C. tangerina oil (22.1 mg/mL and 72.5 µM TE/g, respectively; p < 0.05). Both oils showed broad-spectrum antibacterial activity (MIC range 312–1250 µg/mL), with C. sinensis being significantly more potent against Listeria monocytogenes and Citrobacter freundii ( p < 0.05). In the antileishmanial assay, C. sinensis oil displayed a lower IC₅₀ (24.8 µg/mL) compared to C. tangerina oil (32.3 µg/mL; p = 0.041). Citrus sinensis peel oil consistently outperformed C. tangerina oil, likely due to its minor monoterpenes β-pinene and δ-3-carene. These preliminary findings, combined with the valorisation of citrus waste, suggest that the oils, particularly from C. sinensis , warrant further investigation as potential natural additives for food or cosmetic applications, pending safety and efficacy studies.