Variability of phenolic compounds and antioxidant activities of ten Ceratonia siliqua L. provenances

Abstract

In the present study, Tunisian carob (Ceratonia siliqua L.) pulp samples harvested from ten different geographic regions (Bizerte, Beja, Ariana, Ben Arous, Jendouba, Siliana, Zeghouan, Nabeul, Sousse, Kairouan) were analyzed for their bioactive phytochemical content and antioxidant activities. Total phenolics (TPC), flavonoids (TFC), condensed tannins (CT) were determined using Folin-Ciocalteau, aluminium trichloride (AlCl3) and vanillin assays, respectively. Significant variations (p < 0.05) in total polyphenols (TPC), flavonoids (TFC) and condensed tannins (CT) contents were observed between the analyzed provenances. The highest levels of TPC (23.11 mg GAE/g DR) and TFC (10.58 mg CE/g DR) were detected in Kairouan site, whereas Beja sample exhibited the higher amount of CT (3.75 mg CE/g DR). Reversed phase RP-HPLC analysis revealed that gallic acid (501.26–1628.46 mg/kg), ellagic acid (398.85–940.53 mg/kg) and isoquercetin (264.79–817.61 mg/kg) were the major phenolics in all studied extracts, with concentrations varying significantly according to the geographical origin. Using total antioxidant capacity, DPPH, ABTS and FRAP assays, carob pulp extracts were found to have substantial antioxidant activities, which were correlated to their phenolic contents. Multivariate statistical analysis (PCA) performed on phenolic profiles and antioxidant activities revealed three distinctive groups of samples. It was concluded that Ceratonia siliqua L.. pulp from lower semi-arid and upper arid regions of Tunisia presented appreciable amount of phenolic compounds and high antioxidant capacities. This resource deserves further attention mainly for its high potential in culinar, pharmaceutical and cosmetic utilisations.