Pumpkin Peel Flour Extracts Obtained by an Ultrasound-Assisted System as a Rich Source of Bioactive Compounds with Antioxidant Properties

This study evaluated an Ultrasound-Assisted solid-liquid Extraction (UAE) aided by Response Surface Methodology (RSM) to obtain bioactive-rich extracts from pumpkin ( Cucurbita moschata ) dried peel. Total Phenolic Compounds (TPC), Total Flavonoids Content (TFC), as well as the in vitro Antioxidant Activity (AA), were assessed. The physicochemical analysis revealed that Pumpkin Peel Flour (PPF) has an excellent nutritional profile, comprised by lipids (11.80%), proteins (6.02%) and total fibre (1.96%), in addition to valuable quantity of minerals such as P, Mg, Ca, Fe, Na, Zn and Mn. A Box-Behnken design was applied to analyse the effect of the concentration of solvent, the extraction time and the solid-liquid ratio as independent variables and the TPC, TFC and AA in response. PPF is a rich source of TPC (145.51-479.05 mg GAE/L) and TFC (44.08-89.68 mg CTE/L), which contribute to a high antioxidant activity (653.90-1698.20 &mumol TE/L). Using the RSM, a simultaneous optimisation was performed by the desirability function and the optimum condition to maximise the obtaining of target compounds was with 80% ethanol in the proportion of 10 mL/g (solvent vs raw material) during 45 min. External validation was subsequently conducted on the proposed optimal point and all results were within ±95% of the prediction intervals proposed by the models. Thus, the UAE aided by RSM was shown to be an adequate approach to model the recovery of bioactive compounds with antioxidant properties from a by-product of the pumpkin industry.