Chitosan Coating Loaded with Spearmint Essential Oil Nanoemulsion for Antifungal Protection in Soft Citrus (Citrus reticulata) Fruits

In this study, chitosan (CH) was loaded with spearmint (S) essential oil nanoemulsion (EO) to provide antifungal properties during the postharvest storage of soft citrus fruits. (S)-EO (2%) nanoemulsion–CH (0.8%) coatings inhibited 100% of Penicillium italicum and Penicillium digitatum radial mycelial growth and spore germination in vitro. The (S)-EO (2%) nanoemulsion–CH coating (0.8%) enhanced the antifungal activity by achieving 100% inhibition of P. digitatum in soft citrus cultivars ‘Nova’ and ‘Tango’ compared to the control in vivo. However, P. italicum decay was reduced to 33% and 18% in ‘Nova’ and ‘Tango’ soft citrus compared to the control. The (S)-EO (2%)-CH nanoemulsion coating system prepared by high shear homogenization showed a particle size of 252.3 nm and zeta potential of +21.6 mV, indicating changes in molecular interactions and structural reorganization between EO and CH. The polydispersity index values indicated a stable system. pH remained acidic, antifungal activity was favored, and the incorporation of the EO nanoemulsion improved the thermal stability of the CH coating. The optical properties showed less transparency and more opacity. Despite cultivar differences affecting host specificity, the study recommends using a 2% (S)EO nanoemulsion–CH (0.8%) coating instead of synthetic chemicals to extend citrus fruit storage life.