Bioactive properties of guaco (Mikania glomerata Sprengel) leaf extracts produced with different hydroalcoholic solvents

Even though guaco (Mikania glomerata Sprengel) is a promising source of active compounds, its antioxidant and antimicrobial activities remain underexplored. Thus, this study aimed to produce guaco leaf hydroalcoholic extracts with significant antioxidant and antimicrobial activities while ensuring their safety (GRAS). Guaco leaf hydroalcoholic extracts were prepared at 60 °C using hydroalcoholic solvents with varying concentrations (0, 20, 40, 60, 80, and 100% v/v) of ethanol or methanol for comparison. Characterization included soluble solids, chlorophylls, carotenoids, phenolic compounds, and flavonoid concentrations, alongside antioxidant activity (ABTS•+ and FRAP) and antimicrobial activities. The guaco leaf hydroalcoholic extracts that showed the highest antioxidant activities, as assessed by the FRAP method, were those containing 40% and 60% of ethanol with 28.0 and 26.4 mg Trolox/g dry matter, respectively, as well as the extracts with 60% and 80% of methanol with 27.7 and 23.5 mg Trolox/g dry matter, respectively. Data obtained from ABTS antioxidant assays also showed this same trend. The extracts with the highest antioxidant activities – GLHeE.40, GLHeE.60, GLHmE.60 and GLHmE.80 – generally exhibited simultaneously high soluble solids (1.3; 1.6; 2.3; and 2.6 °Brix, respectively), intermediate carotenoids (0.15; 0.22; 0.12; and 0.16 mg/g dry matter, respectively), the highest phenolic compounds (13.5; 12.4; 11.5, 11.3 mg gallic acid/g dry matter, respectively), and flavonoids (9.11, 8.95, 7.01 and 11.3 mg catechin/g dry matter, respectively). The hydroethanolic extracts containing 40% and 80% ethanol showed antimicrobial activity against Listeria monocytogenes, with inhibition zones ranging from 1.0 to 1.5 cm in diameter. These findings indicate that ethanol is an effective solvent for producing guaco leaf hydroalcoholic extracts, thereby enhancing their antimicrobial properties while preserving their antioxidant activity.