Antioxidant properties of lemon essential oils: a meta-analysis of plant parts, extraction methods, dominant compounds, and antioxidant assay categories

Abstract

Recent studies have explored the antioxidant properties of lemon essential oil (LEO), taking considering factors like plant part, extraction methods, and antioxidant assay. However, due to varied results and limited precision in individual studies, our meta-analysis aims to offer a comprehensive understanding across different experiments, irrespective of location or time. Out of 109 scientific articles published between 1947 and 2024, only 28 successfully validated their data on differences in antioxidant capacity and IC50, using weighted averages of Hedges’ d in meta-analysis. A meta-analysis revealed several key findings: (i) lemon leaf and peel extracts have higher IC50 compared to controls, whereas whole plant extracts show lower values (p < 0.001); (ii) the maceration preserves antioxidant properties better than hydro-distillation and Soxhlet extraction (p < 0.001); (iii) LEO require higher concentrations to achieve comparable free radical inhibition as the standard controls such as AsA, BHT, and quercetin, suggesting lower antioxidant efficiency. This was supported by IC50 result, which showed no significant difference between LEO and other compounds like thymol, Thymus vulgaris EO, and Citrus aurantium EO. However, compared to AsA, BHT, limonene, and trolox, the inhibition efficacy was significantly lower (p < 0.01). These findings consistently demonstrated significant antioxidant activity across multiple assays, including ABTS, β-carotene bleaching, DPPH, and FRAP (p < 0.01). Notably, the predominant components of LEO including α-linoleic acid, D-limonene, limonene, L-limonene, neryl acetate, sabinene, and Z-citral, which demonstrate significant potency as antioxidant agent (p < 0.01). Specifically, limonene and Z-citral make substantial contributions to its antioxidant capacity (p < 0.01). Despite variations in purity among LEO extractions, there is potential for future enhancement through nanoemulsion. In conclusion, LEO show promise as an alternative antioxidant, with emphasis to selecting samples based on leaves or peels and employing maceration extractions for various antioxidant assays. Active components rich in terpenoids, such as limonene and Z-citral, are particularly noteworthy. Graphical Abstract: (Figure presented.)