Optimized microwave-assisted extraction of total phenolic and flavonoid contents from defatted seeds and press residue of Opuntia ficus-indica (l.) mill

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Phenolic content of Opuntia ficus indica (OFI) was estimated in samples of seeds and press residue (cake) generated through mechanical oil extraction process. A microwave-assisted extraction (MAE) method was investigated for the optimization of the extracted total phenolic (TPC) and total flavonoid contents (TFC). The influence of extraction parameters on the yields of TPC, TFC were modelled using a second-order regression equation. The optimal MAE conditions were: 61.65 % ethanol concentration, 633.42 W microwave power, 3.59 min irradiation time and 46.28 mL/g solid-to-liquid ratio (SLR) for phenolics extraction, and 54.97 %, 580.04 W, 3.20 min and 47.40 mL/g for flavonoids extraction from defatted seeds powder. The extracts obtained under these conditions showed a TPC and TFC of 416.311±1.154 mg gallic acid equivalent (GAE) per100 g dry weight (DW) and 52.67±0.72 mg quercetin equivalent (QE)/100 g DW, respectively. Regarding press residue, the optimal conditions were 60.26%, 643.89 W, 3.85 min and 47.28 mL/g for phenolics extraction, and 67.96 %, 464.41 W, 2.46 min and 41.04 mL/g for flavonoids extraction; with a TPC and TFC of 400.11±3.14 mg GAE/100 g DW and 38.75±0.16 mg QE/100g DW, respectively. The results of the present study confirmed that OFI seeds and press residues could be considered as a non-negligible source of phenolics with a good antioxidant activity and revealed that MAE is a reliable method for optimizing yields of recovered phytochemicals from such agricultural products derivatives and by-products, with an intent to be scaled-up for industrial, nutraceutical or pharmaceutical applications.