The Second Life of Citrus: Phytochemical Characterization and Antifungal Activity Bioprospection of C. limon and C. sinensis Peel Extracts Against Potato Rot Disease

Purpose: Citrus peel is known to contain a number of secondary metabolites effective against some phytopathogenic fungi affecting crop production both in the field and during storage. As fruit peels from the production of citrus juice are secondary waste that accounts up to the 40–50% of the total product biomass, the recycling of these by-products for the extraction of natural fungicides perfectly accomplishes the concept of circular economy in the food supply chain. Methods: We obtained essential oils and aqueous extracts from dried peel of Citrus limon and C. sinensis, determined the residual phytochemical profile and assessed their biological activity against Fusarium solani and Pythium ultimum, etiological agents of potato rot disease. Aqueous extracts composition was characterized by GC–MS, while essential oils were characterized with HPLC–DAD. Results: Five main compounds (quinic acid, protocatechuic acid, caffeic acid, rutin and kaempferol) were found to differentiate the two citrus peels, while syringic acid detected as main compound in C. sinensis was not found in C. limon. The antifungal activity, evaluated in term of both spore germination inhibition and mycelial development impairment, showed a lower antifungal potential of C. sinensis extracts with respect to C. limon. Conclusions: C. limon peels possibly obtained from recycled food waste could be therefore considered for sustainable agriculture and food conservation purposes against potato rots fungi.