Biofungicidal Activity and Antioxidant Properties of Essential Oils from Mentha pulegium and Cymbopogon citratus: Protection Against Lipid Oxidative Damage

Essential oils (EOs) have gained attention as biodegradable biopesticides for sustainable crop protection. This study investigated the chemical composition, antifungal activity and antioxidant potential of EOs from Mentha pulegium (EO-MP) and Cymbopogon citratus (EO-CC) against Bipolaris oryzae, the causal agent of rice brown spot, including the first quantitative determination of IC50 values through standardized dose–response modeling and temporal evaluation of antifungal efficacy. Volatile profiles of both EOs were characterized by gas chromatography coupled with flame ionization detection (GC-FID) and gas chromatography–mass spectrometry (GC-MS). Antifungal activity was evaluated in vitro by a poisoned food assay at six concentrations ranging from 9.375 to 300 µL per plate (0.469–15.000 µL/mL PDA medium). Mycelial growth inhibition was assessed after 7 and 14 days of incubation. Antioxidant potential was determined by ferric reducing antioxidant power (FRAP) assay while protection against lipid oxidative damage was evaluated through inhibition of lipid peroxidation by the thiobarbituric acid reactive substances (TBARS) method. Both EO-MP and EO-CC exhibited strong, dose-dependent antifungal effects and achieved complete inhibition of mycelial growth at ≥37.50 µL per plate (1.875 µL/mL PDA) and ≥18.75 µL per plate (0.938 µL/mL PDA), respectively. EO-MP showed high reducing capacity (its FRAP value was 1.45 Trolox equivalent antioxidant capacity—TEAC) and high inhibition of lipid peroxidation (89.09%). Similarly, EO-CC exhibited a FRAP value of 1.55 TEAC and lipid peroxidation inhibition of 87.66%. These findings highlight the biofungicidal activity and multifunctional antioxidant-related properties of EOs from M. pulegium and C. citratus, supporting their potential application as eco-friendly tools for sustainable rice brown spot management.