Recovery of Bioactive Phenolic Compounds from Cork Industry Waste Using Ultrasound and Microwave Techniques

Abstract

This work determined the most efficient technique to extract phenolic compounds from cork-processing wastes using ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE). Bearing this, the total phenolic compounds (TPCs) identified through LC-DAD-MS/MS analysis and the extraction yield (EY) were analyzed. Different UAE and MAE conditions on the EY and TPC were investigated by using RSM with a central composite design. Optimal UAE conditions (20 min and 75% ethanol concentration) resulted in an EY of 23.74 ± 3.71 mg extract/g dry weight and a TPC of 0.69 ± 0.03 mg/g dw. For MAE, the best conditions (25 min, 150 °C, and 90% ethanol) resulted in an EY of 127 ± 7 mg/g dry weight and a TPC of 1.85 ± 0.30 mg/g dry weight. Compared with conventional maceration (7 d, 35 °C, 50% ethanol), MAE increased the TPC by 40% with a 2-fold EY. Also, it almost doubled the amount of TPC and EY achieved from UAE in half the time. Antioxidant features were assessed by measuring the antiradical properties (DPPH) and the reducing power (FRAP). Overall, the application of MAE presents a viable, time-efficient, and high-yield alternative for enhancing the extraction of bioactive compounds from cork byproducts, aligning with the principles of a circular economy.