Sustainable PLA–Citronella Essential Oil Films: Development and In Vitro Antifungal Evaluation for Potential Blueberry Packaging Applications

Postharvest fungal decay is a primary cause of losses in blueberries, motivating the development of sustainable alternatives to conventional fungicides. This study aimed to develop and evaluate antifungal active films based on polylactic acid (PLA) enriched with citronella essential oil to control phytopathogenic fungi associated with blueberry spoilage. PLA films containing 7.5, 10, and 12.5% (<i>w</i>/<i>w</i>) citronella essential oil were produced by solvent casting and characterized for water vapor transmission rate and nanomechanical properties. The antifungal effect was tested <i>in vitro</i> against <i>Epicoccum nigrum</i>, <i>Alternaria alternata</i>, and <i>Cladosporium herbarum</i>. Active films exhibited concentration-dependent antifungal activity, with <i>C. herbarum</i> being the most sensitive fungus. The incorporation of citronella essential oil did not significantly alter the water vapor barrier properties of PLA, while mechanical analysis revealed a reduction in elastic modulus only at the highest concentration. The antifungal mechanism was elucidated using scanning electron microscopy, fatty acid profiling, absorbance at 260 nm, and conductivity measurements. The results indicate that the released citronella essential oil induced membrane disruption and morphological damage in fungal hyphae, with species-specific responses. Overall, PLA-citronella essential oil films represent a promising biodegradable packaging solution to control postharvest blueberry losses.