Optimization of ultrasound-assisted extraction and LC-ESI–MS/MS analysis of phenolic acids from Brassica oleracea L. var. sabellica

• The aim of review was to optimize ultrasound-assisted extraction of phenolic acids from Brassica oleracea L. var. sabellica (kale).
• Four solvents and two extraction times with ultrasound frequency 20 kHz and power 100 W were examined.
• The most effective conditions for the isolation of phenolic acids are 80% aqueous ethanol and extraction time 60 min.
• High performance liquid chromatography-mass spectrometry for quantitative analysis was performed.
• Thirteen phenolic acids were isolated.

Vegetables belonging to the Brassica oleracea group are an important source of bioactive metabolites, especially phenolic acids and flavonoids. A literature search did not yield any reference about earlier reports on the ultrasound-assisted extraction (USAE) of phenolic compounds from B. oleracea L. var. sabellica (kale). Therefore, the aim of this review is to optimize USAE for LC-ESI–MS/MS analysis of these compounds from kale.In the experiment four solvents, (ethanol and ethanol, 80% aqueous ethanol, methanol and 80% aqueous methanol) and two extraction times, (40 and 60 min) with ultrasound frequency 20 kHz and power 100 W, were examined. The most effective conditions for the isolation of phenolic acids are 80% aqueous ethanol and extraction time 60 min. USAE can offer high yield of analyzed compounds in short time, simple manipulation and reduced volume of solvent. Techniques used in experiment proved to be repeatable methods, as evidenced by the RSD% values.