Optimisation of the extraction process of antioxidant capacity compounds from beet (Beta vulgaris L.) stalk

Abstract

Beet is a traditional root consumed worldwide and is considered a potential source of several bioactive compounds, yet during production and commercialisation activities, its leaves and stalks are discarded. The beet residue has notable quantities of diverse phenolic compounds that are not taken advantage of it. The beet stalks (sample) were obtained from a local producer at the municipality of Marechal Cândido Rondon, Paraná state, Brazil. The optimisation of the extraction process of antioxidant capacity compounds from beet stalk was done by response surface methodology (RSM), with three independent variables (time, from 5 to 85 min; temperature, from 20 to 80 °C and solvent, from 0 to 100% of ethanol/ water ratio). Extracts were evaluated for their reducing capacity, measured by the Folin-Ciocalteu method, and antioxidant capacity by the ability to scavenge DPPH and ABTS free radicals. The optimal global extraction conditions determined were 5 min, 80 °C and 50% ethanol, yielding 13.157 mg gallic acid equivalents (GAE) g-1, 21.539 µmol Trolox equivalents g-1 (TE; DPPH) and 250.190 µmol TE g-1 (ABTS). Beet stalk demonstrated to be an alternative and rich source of recovering of natural antioxidant compounds, showing higher contents when compared to other agro-industrial residues.