Sustainable valorization of citrus pomace waste: biochar production and in vitro bioactivities

In recent years, biochar, a carbon-rich material, has gained increasing interest in zootechnical applications due to its potential antioxidant and antimicrobial properties. Sicily is the leading citrus-producing region in Italy, generating large amounts of agro-industrial waste, which can be converted into biochar, representing an innovative approach. This study investigated the chemical composition, mineral content, morphology, enzymatic digestibility, antioxidant and antimicrobial activity of biochar obtained by pyrolysis of whole lemon pomace (WB) and depectinized lemon pomace (DB). WB and DB biomasses were pyrolyzed at 600 °C for 60 min. Samples were analyzed for bromatological and mineral composition; morphological characterization was evaluated through SEM, and antioxidant analysis through ABTS assay for biochar extracts. Antimicrobial activity was evaluated using a microdilution method. WB extract exhibited higher antioxidant and antimicrobial activity against E. coli compared to DB extract, with an antioxidant activity of 306.79 ± 22.23 μg of TE/g (p < 0.001). Potential undesirable elements were very low in both samples. Particularly, copper was lower in DB, while zinc was higher in DB (p < 0.0001). SEM analysis revealed macropores and mesopores attributable to xylem vessels and fibers in both biochar samples: WB sample exhibited values up to 35 μm and down to 15 nm; DB revealed pores from 20 μm to 200 nm. These findings highlight the value of citrus pomace biochar extracts for their potential antioxidant and antimicrobial properties against E. coli, demanding further in vivo investigations to confirm its efficacy and benefits in livestock.