In vitro evaluation of biochar from chestnut and vine residues gassification as possible feed additive: antioxidant and antimicrobial activities

Biochar has been used for different agriculture and environmental applications to minimize waste and increase the circular economy's efficiency. Particularly, the use of biochar as a feed ingredient has the potential to improve animal health, feed efficiency, and livestock housing climate. In the scientific understanding, it is still unclear why biochar, as a feed additive, promotes the observed effects. The variability in physical-chemical-biological properties depends on pyrolysis temperature and waste used. In the present work, two different biochar from (i) chestnut waste (CB) and (ii) vine residues (VB) were characterized for chemical composition and functional properties. The chestnut and vine biochar were extracted into hot water (90 °C for 3 h head-over-heels) and the extracts were analyzed for inorganic/organic components by HPLC-MS. The antioxidant activity was determined by a colorimetric assay (ABTS assay). The antioxidant activity of vine biochar is significantly higher than chestnut biochar (110 TE/gr vs 54 TE/gr; p ≤.01). In the present study, the extracts were tested for their effects on in vitro growth inhibitory activities against enterotoxigenic E. coli species. Overnight grown E. coli were inoculated into tubes containing 20mL of Luria-Bertani medium (LB) supplemented with 0, 25, 50, and 100 μL/mL of biochar water extracted. Tubes were cultured aerobically at 37 °C and the bacterial growth rate was determined spectrophotometrically by optical density at 600nm (at 60min intervals for 6h). The same concentrations of biochar extract (0, 25, 50, and 100μL/mL) were tested on growth of L. plantarum and L. reuteri cultured in MRS broth. The optical density at 600nm was checked every 2 h for a total of 12 h. Our results demonstrate that both biochar extracts exerted a significative inhibitory activity dose depending (p ≤. 01) against pathogenic E.coli strains; the maximum percentage of inhibition, corresponding to a reduction of 29% of bacterial cells, was observed after 2–3 h of incubation with 100 μL/mL of biochar extracted. On the contrary, the growth of L. plantarum and L. reuteri was not negatively influenced. Significant differences between groups were performed by one-way ANOVA (GraphPad Prism). These preliminary results suggest that an appropriate dosage of biochar may be interesting to inhibit the growth of pathogenic E. coli and consequently a valid alternative for the reduction of the use of antibiotics.