Valorization of spinach roots for recovery of phenolic compounds by ultrasound-assisted extraction: characterization, optimization, and bioaccessibility

In this study, the total phenolic content (TPC), the total flavonoid content (TFC), antioxidant activity (TAA), phenolic compounds composition with liquid chromatography–tandem mass spectrometry (LC–MS/MS), and mineral compounds composition with inductively coupled plasma mass spectrometry (ICP-MS) of spinach roots were determined. In addition, the aim of the study was to obtain bioactive components from spinach roots by ultrasound-assisted extraction method. Ultrasound-assisted extraction was performed with a probe-type ultrasonic homogenizer, and extraction variables were determined as amplitude (25–55%), temperature (10–30 °C), time (3–5 min), and ethanol concentration (20–60%). The process conditions were optimized using the response surface method and a central composite design. The effects of extraction variables on the TPC, TFC, and TAA of spinach roots were investigated in the optimization process. The maximum amount of phenolic compound, flavonoid compound, and antioxidant activity were determined as 5579.51 mg GAE kg −1 LW, 1824.34 mg CE kg −1 LW, and 20.79 mmol TE kg −1 LW under the optimum extraction conditions of time (3 min), temperature (10 °C), amplitude (55%), and ethanol concentration (20%). The predictive capabilities of the proposed quadratic polynomial models were found to be sufficient as the experimental and predicted data were consistent with each other. The ultrasound-assisted extraction improved the bioaccessibility of phenolic compounds spinach roots in the stomach. The ultrasound-assisted extraction can be considered as an efficient, green, and practical technique for recovering bioactive components from spinach roots.