Antifungal effect of Algerian essential oil nanoemulsions to control Penicillium digitatum and Penicillium expansum in Thomson Navel oranges (Citrus sinensis L. Osbeck)

Fungal infection is a potential issue in citrus fruits, while essential oils from <i>Cymbopogon citratus</i> and <i>Citrus limon</i> could be better alternatives to synthetic fungicides in orange preservation. The nanoparticles produced during ultrasonication exhibited a monomodal distribution of particle sizes with a mean zeta potential and a polydispersity index mean value of 74.12 nm, -38.4 mV, and 0.19 for <i>C. citratus</i> and 103 nm, -28.4 mV, and 0.22 for <i>C. limon</i>. The micrographs of the nanoemulsions exhibited spherical morphology with diverse nanometer-scale sizes. Nanoemulsification enhances the levels of neral and geranial in both oils while reducing the levels of limonene, γ-terpinene, and β-myrcene. The essential oils and their nanoemulsions exhibited good MIC values against Gram-positive and Gram-negative bacteria, ranging from 2% to 0.12%, while MBC was 4% to 0.25% (v/v) for both. The extended genetic investigation of the isolated fungal strains from Thomson Navel oranges through analysis of the ITS sequences and BLAST indicated 100% homology to those of <i>Penicillium digitatum</i> and <i>Penicillium expansum</i>. Both oils' MIC and MFC values and nanoemulsions ranged from 0.12% to 0.06% and 2% to 0.03% against <i>P. expansum</i> and <i>P. digitatum</i>, respectively. Applying nanoemulsified <i>C. limon</i> and <i>C. citratus</i> as a coating on orange fruits significantly reduced the spread of <i>P. expansum</i> and <i>P. digitatum</i> fungi compared to the control. Coating with nanoemulsions reduced the negative changes in quality parameters during storage, such as weight loss, firmness, TSS, TA, pH, and ascorbic acid content. <i>Citrus limon</i> nanoemulsion did not alter the coated fruits' sensory attributes compared to <i>C. citratus</i> nanoemulsion.