Single and interactive effects of process variables on antioxidant content and antioxidant activity of vegetable aqueous extracts obtained by conventional and microwave-assisted extractions

The aim of this work was to study the single and interactive effects of process variables in microwaveassisted and conventional extraction of antioxidant compounds from asparagus, cauliflower, celery, and chicory wastes using water as solvent. The following variables were investigated: water/sample ratio, extraction time in microwave-assisted extraction; water/sample ratio, extraction time, temperature in conventional extraction. Concerning the microwave-assisted extraction, the highest phenolic recoveries and the highest antioxidant activity were obtained at a solid-to-liquid ratio of 1:2 (w/w) and prolonging the time of treatment up to 4 min. In the conventional extraction system, the highest yields were generally obtained at a solid-to-liquid ratio of 1:2 (w/w) and with the combination high temperature-low time of treatment. Cauliflower and chicory wastes showed the highest extraction yields when submitted to microwaves and conventional extraction, respectively. Catechin, ascorbic acid, and quercetin 3-O-glucopyranoside were the main phenolic compounds identified in wastes. The application of conventional extraction system gave higher extraction yields than the microwave-assisted one