Utilization of Guarana Agroindustrial Waste as a Source of Antimicrobial Compounds for Human Pathogenic Bacterial...

The guarana seed peel (GSP), an agroindustrial waste, was characterized for its chemical composition and evaluated for its antimicrobial activity as a potential source of antibacterial compounds for wastewater disinfection using UPLC-QTOF-MS analysis. UPLC-QTOF-MS analysis of GSP, its raw extract (GSPE), and its purified extract (GSPP) identified 36 compounds, including catechin and its oligomers: a B-type procyanidin dimer, pavetannin B6 (trimer), and cinnamtannin A2 (tetramer). Principal component analysis (PCA) separated GSPE from GSPP along PC2, and the purification step concentrated flavonoids-mainly catechin and its oligomers-in GSPP. Antimicrobial activity was assessed against the human pathogens Escherichia coli and Salmonella typhimurium, causing gastroenteritis and invasive disease, and Staphylococcus aureus, causing skin and invasive infections. In real wastewater, GSPE (500 mg L^-1) reduced total coliforms by up to 81 ± 7% and E. coli by up to 74 ± 7% within 180 min. Confocal microscopy with the LIVE/DEAD^® BacLight™ kit (Thermo Fhisher, Eugene, OR, USA) confirmed loss of membrane integrity in GSPE-treated Escherichia coli, and disc diffusion with GSPP produced inhibition zones of 9-11 mm against Staphylococcus aureus, Escherichia coli and Salmonella typhimurium at 5 mg per disc. These results show that guarana seed peel-currently discarded-is a viable source of catechin-rich antibacterial extracts for wastewater disinfection.