Comparison of Three Extraction Protocols for the Characterization of Caper (Capparis spinosa L.) Leaf Extracts: Evaluation of Phenolic Acids and Flavonoids by Liquid Chromatography – Electrospray Ionization – Tandem Mass Spectrometry (LC–ESI–MS) and the Antioxidant Activity

Three extraction methods, involving maceration, reflux, and ultrasonic extractions, were used to evaluate the phytochemical content and antioxidant activity of leaf extracts from Capparis spinosa L. collected from five localities in South Tunisia. The results showed that the maceration extract contained the highest content of phenolic acids and flavonoid compounds. The maceration extraction method exhibited the highest antioxidant activities using the reducing power assay, the azinobis (3-ethylbenzothiazoline)-6-sulfonic acid (ABTS+), and the 2,2-diphényl-1-picrylhydrazyle (DPPH°) radical scavenging activity. The determination of the phytochemicals in the extracts was carried out using a quadrupole mass spectrometer equipped with an electrospray ionization source that was operated in the negative ionization mode (LC–ESI–MS). The results allowed the detection of seven phenolic acids in the maceration extract and ultrasonic assisted extraction, but only six phenolic acids in the reflux extract. The major identified phenolic acids were quinic acid, gallic acid, and protocatchuic acid. Ten flavonoids were detected, and their concentrations varied according to the extraction method. Catechin was the most abundant flavonoid in all of the extracts. This investigation provides additional support for the use of caper leaves in medicinal and food applications.