Single and interactive effects of process variables on microwave-assisted and conventional extractions of antioxidants from vegetable solid wastes

•The effects of conventional and microwave-assisted extraction on antioxidants of vegetable aqueous extracts were studied.•Solid wastes from minimally processed asparagus, cauliflower, celery, and chicory were analyzed.•Water/sample ratio, extraction time, and temperature were investigated in conventional extraction.•Water/sample ratio and extraction time were investigated in microwave-assisted extraction.•The extraction yields were generally higher in the conventional system than in the microwave-assisted system.

The aim of this work was to study the single and interactive effects of process variables in microwave-assisted 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.