Cork by-products as a sustainable source of potential antioxidants

Abstract

Cork harvesting process is considered sustainable, however, the potential of the waste that is generated in the cork transformation process, in the context of bio-circular economy, still needs more investigation. This work investigated three cork by-products, coarse powder (P0) and fine powder (P1), as well as cork boiling wastewater (CBW), as sustainable sources of value-added ingredients with antioxidant potential for pharmaceutical, food products and the cosmetic industry. The free radical scavenging effect and the metals content of P0 and P1 extracts and CBW was evaluated. A low content of metals was detected for P0 and P1 powders, while CBW showed high levels of the prohibited heavy metals As and Pb, among other metals, above the permissible trace amounts allowed in cosmetics, pharmaceuticals and food products. The extractive process was optimized by taking into account the effect of temperature, solvent, extraction time and number of extraction cycles on DPPH scavenging activity and process sustainability. Liquid chromatography coupled to the high-resolution mass spectrometry and ultraviolet–visible detection allowed the unequivocal identification and quantification of the target compounds, respectively. All extracts displayed promising DPPH scavenging effect, being P1 extract obtained with 30% ethanol (IC50 = 4.7 ± 0.2 μg/mL) the most active. The DPPH scavenging effect of cork powder extracts could be explained by the efficiency of extraction of phenolics. This work allied clean and environmentally friendly processes by the use of green solvents and low energy consumption in the extraction procedures. The relationship between chromatographic patterns and the antioxidant activities was also explored.