Sustainable valorization of red prickly pear seeds: Green technologies for antioxidant compounds recovery

Although Prickly pear seeds are agroindustrial wastes, these residues are a natural source of antioxidant compounds. Thus, this study analyzed two green technologies like Pressurized Liquid Extraction (PLE) and Ultrasound-Assisted Extraction (UAE) combined with water-ethanol mixtures at different temperatures (50 °C and 70 °C) to recover antioxidant compounds from red prickly pear seeds. The use of UAE process combined with 60% ethanol at 70 °C was 55% more effective to recover antioxidant compounds compared to the PLE process (60% ethanol–70 °C). Under these conditions, the extracts presented a high total polyphenol content (1.65 mg GAE/g dw), DPPH radical inhibition capacity (IC50: 15.5 mg/mL), and oxygen radical inhibition capacity (48.6 μM ET/g dw). For polyphenol profile, increasing the ethanol concentration at 70 °C allowed to recover higher concentrations of caffeic acid, catechin and procyanidins. However, the quercetin was negatively affected by the increased ethanol concentration. Principal component analysis indicated that temperature and solvent composition are key parameters for the selective extraction of antioxidant compounds. Finally, the UAE process was 35% more efficient than conventional extraction to recover antioxidant compounds. These results show the feasibility of scaling up to an industrial level a sustainable process to recover metabolites from agroindustrial waste.