Lemongrass (Cymbopogon flexuosus) Essential Oil Nano-Biofilm for Postharvest Management of Orange (Citrus sinensis): Ultrasonic Extraction Optimization, Colloidal Characterization, and Antifungal Efficacy against Alternaria alternata

¹ Amity Institute of Horticulture Studies and Research, Amity University, Noida, Uttar Pradesh 201301, India
² Amity Food & Agricultural Foundation, Amity University, Noida, Uttar Pradesh 201301, India

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Abstract

Postharvest fungal spoilage, principally caused by Alternaria alternata, results in significant losses of citrus fruits during storage and transport. This study developed and evaluated a biodegradable nano-biofilm based on lemongrass essential oil (LEO) from Cymbopogon flexuosus, rich in citral, as a sustainable alternative to synthetic fungicides for the postharvest preservation of oranges (Citrus sinensis). Preliminary screening compared the Soxhlet-derived hexane extract and the hydrodistilled essential oil; based on extraction yield and antifungal efficacy, hydrodistillation was selected for further optimization via ultrasonic pretreatment (UPHD), yielding 1.25% under optimized conditions (30 °C, 25 min), compared with 0.91% for the untreated control. The nano-biofilm was formulated with sodium alginate and Tween 80; dynamic light scattering (DLS) characterization revealed a Z-average droplet diameter of 178.6 nm (PDI = 0.269), confirming a stable, narrow-distribution nano-emulsion. In vitro antifungal assessment using the poisoned food technique demonstrated complete inhibition of A. alternata at 1000 ppm, whereas the control and biopolymer treatments showed unrestricted fungal growth. In vivo application of 5% and 2.5% LEO coatings on inoculated oranges prevented visible fungal infection and maintained fruit quality; 1.25% LEO provided partial protection with minor shrinkage. Shelf life was extended by up to 10 days under ambient storage. These findings establish LEO-based nano-biofilm as a physicochemically stable, biologically active, and ecologically sound postharvest coating system.