PHENOLIC CONTENT AND ANTIOXIDANT ACTIVITY OF CAROB (Ceratonia siliqua L.) LEAF EXTRACTS OBTAINED BY GREEN EXTRACTION TECHNIQUES

In recent years, a growing demand on functional products enriched with naturally derived ingredients has raised interest in finding new sources of bioactive molecules as well as establishing optimal isolation technologies that would allow their fast and efficient isolation. Various green extraction technologies, such as ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE) and pressurized liquid extraction (PLE) have emerged due to their main advantages of reducing the extraction time, energy and solvent consumption while achieving higher extraction efficiency and lower degradation of targeted compounds compared to conventional extraction techniques. Carob tree (Ceratonia siliqua L.) is a Mediterranean plant belonging to the Fabiaceae family which has recently drawn attention due to the nutritional value of its pods, while other plant parts, such as leaves, have been researched to a lesser extent. Since the health beneficial properties of polyphenols are well known, the aim of this research was to evaluate carob leaves grown in south Croatia as a source of polyphenols by analyzing the phenolic content and antioxidant activity of carob leaf extracts obtained by three different green extraction techniques (UAE, MAE and PLE). The extractions were carried out on a sample of grinded dry carob leaves for 10 min at a temperature of 80°C, sample: solvent ratio 1:20 and 50% aqueous ethanol as a solvent. The frequency in UAE was 37 kHz, microwave power in MAE 500 W and PLE was set to 1 static cycle. The total phenolic content (TPC), hydroxycinnamic acids content (HAC) and flavonol content (FC) were determined by spectrophotometric methods, while the antioxidant activity was determined by DPPH Radical Scavenging and Ferric Reducing Antioxidant Power (FRAP) assays. It was shown that carob leaves can be considered a source of phenolic compounds since the TPC was in the range of 51.86–64.81 mg gallic acid equivalents (GAE) g-1 . The extracts have also shown high antioxidant activity with values of 25, 10–28, 90 mM Trolox equivalent (TE) g-1 and 22, 92– 51, 23 mM TE g-1 as determined by DPPH and FRAP, respectively. The extraction techniques have significantly influenced all of the examined parameters and MAE was shown to be the most suitable for achieving maximum TPC, HAC, FC and antioxidant activity as determined by DPPH. The results highlight the importance of research of different extraction techniques that would allow the highest recovery effectiveness and utilization of the plants’ beneficial properties.