Application of bioactive compounds in food bio-preservation and infection protection

Abstract

Fungal contamination of citrus crops represents a significant issue in Algeria. The primary aim of this study is to limit fungal growth on orange fruits using the nanoemulsions obtained from plants of Origanum majorana, Citrus limon, Cymbopogon citratus and Foeniculum vulgare. The essential oils from these plants were extracted using hydrodistillation method, and their nanoemulsions were produced using ultrasonication method. The chemical composition was analyzed using a GC-MS system, and the physicochemical properties of the nanoemulsions were assessed. The antimicrobial efficacy was evaluated in vitro. Furthermore, the antifungal potential of marjoram and fennel was assessed in silico. The GC-MS analysis demonstrated that the nanoemulsification increases the concentrations of terpinen-4-ol and cis-β-terpineol in marjoram, as well as estragole and anethole in fennel, in addition to neral and geranial in both lemon and lemongrass oils, while reducing the levels of α-terpinene, fenchone, limonene, γ-terpinene, and β-myrcene. The nanoparticles exhibited a narrow particle size distribution, indicating high stability and monodispersity of the nanoemulsions. The TEM imaging of the nanoemulsions showed a spherical morphology with diverse nanometer-scale dimensions. The molecular and the phylogenetic analysis of the isolated fungi from orange fruits showed 100% homology to P. expansum and P. digitatum. the essential oils exhibited greater potency compared to their nanoemulsions, with MIC values spanning from 2% to 0.12% against bacteria and from 1% to 0.03% against fungus. Furthermore, the majority of the tested fungi were completely inhibited by lemongrass. On the other hand, F. vulgare showed the weakest antimicrobial activity. Strong binding-free energy values were observed in the interactions between essential oil or nanoemulsions and fungal enzymes, with notable docking scores (−6.6 to −7.0 kcal/mol) for aromatic components. The application of nanoemulsified marjoram, lemon and lemongrass as a coating on orange fruits significantly inhibit the growth of P. expansum and P. digitatum molds compared to uncoated samples. The use of nanoemulsions minimize negative changes in quality parameters of orange fruits throughout storage, encompassing titratable acidity (TA), pH, total soluble solids (TSS), ascorbic acid concentration, weight loss and firmness. The nanoemulsified O. majorana and C. limon did not influence the sensory attributes of the coated fruits as compared to the C. citratus nanoemulsion. Overall, the tested nanoemulsions demonstrated their high efficacy in managing pathogens affecting orange fruits.