Reuse of Hot Trub as an Active Ingredient with Antioxidant and Antimicrobial Potential

The reuse of agro-industrial residues is vital to minimize their environmental impact and alternatives for their application are needed. In this research, we evaluated the chemical composition as well as antioxidant and antibacterial activities of the extract from hot trub, that is the second solid waste obtained during the brewing process. Total phenolic and flavonoids compounds were determined by colorimetric assays and the compounds were identified by UHPLC-DAD-MS/MS. Antioxidant activity was evaluated by ABTS and DPPH methods. Antibacterial activity against Gram-positive and Gram-negative bacteria was analyzed by agar diffusion and microdilution methods. Cytotoxicity was evaluated against murine fibroblast L929 cell line by MTT assay. The results showed that the content of phenolic and flavonoid compounds ranged according to the fractions from 8.237 to 13.390 mg GAE/g and from 0.019 to 1.643 mg QE/g, respectively. The compounds cohumulone, cohulupone, hulupone/adhulupone, isoxanthohumol, xanthohumol, hydroxytricyclocolupone epimers, hydroxytricyclolupone/hydroxytricicloadlupone epimers and nortricyclocolupone were suggested. Higher antioxidant activity was observed for the crude ethanol extract. The hexane fraction presented the lowest MIC value against Gram-positive bacteria, as well as lower cytotoxicity. These results are promising and indicate a great potential for the reuse of this byproduct as a source of natural antioxidant and for the microbiological applications, which consequently would reduce the environmental impact. Graphic Abstract