Recovering and Characterizing Phenolic Compounds From Citrus By-Product: A Way Towards Agriculture of Subsistence and Sustainable Bioeconomy

The valorization of citrus processing waste has a great potential for transition toward a bioeconomy. Hence, the objective of this study was to characterize the phenolic composition profile recovered from the citrus solid waste and its related in vitro antioxidant and antimicrobial activities. Solid waste residues remaining after the juice extraction process of three citrus species, C. aurantium, C. sinensis and C. reticulata were extracted with maceration with hydroethanol mix. Our findings showed that the highest levels of polymethoxyflavones were found in C. sinensis waste extracts, while O-glycosylpolymethoxylated flavonoids were highly accumulated in C. aurantium residue extracts. Luteolin 7-O glucoside, rutin, and myricetin were identified as dominant metabolites of the residue extracts from C. aurantium, C. reticulata and C. sinensis, respectively. Based on relative antioxidant capacity index (RACI) and global antioxidant score (GAS) measurements, the solid waste extracts of C. aurantium exhibited the strongest antioxidant potential. C. aurantium waste extracts were the most active against Gram-positive bacteria and F. oxysporum fungus, while, C. reticulata waste extracts were the most effective against Gram-negative bacteria and the three pathogenesis fungi: B. subtilis, C. albicans and A. flavus. C. sinensis exhibited the highest antifungal activity against A. niger. Correlation analysis highlighted a positive correlation between Gram-positive bacteria and the content in glycosylated metabolites in one hand, and between Gram-negative bacteria and flavonoids in another hand.