Phenolic profile,biological activities and fraction analysis of the medicinal halophyte Retama raetam

Retama raetam is a medicinal and aromatic plant present in the humid to the arid bioclimatic regions of Tunisia. In this work, we investigated R. raetam shoots antioxidant and antimicrobial activities and its natural antioxidant contents obtained from four fractions (petroleum ether, acetone 60%, ethyl acetate and water). Results showed that the ethyl acetate fraction exhibits the highest antioxidant activity as compared to the other ones. In fact, IC₅₀ values of ethyl acetate extract were equal to 33.5, 500 and 1380 μg/ml (DPPH and ABTS radicals scavenging activity and reducing power, respectively). Accordingly, this fraction presented the highest total polyphenol and flavonoid contents (401 mg GAE/g DR and 33.21 mg CE/g DR, respectively). Moreover, RP-HPLC analysis showed that syringic acid and coumarin were the major phenolic compounds. Furthermore, this moderately polar fraction showed considerable antibacterial properties against human pathogen strains especially against Escherichia coli and Bacillus cereus. Finally, fractionation allows the identification of R. raetam most active molecules and therefore the optimization of their utilization. Our findings pointed out the appropriate solvent for extracting R. raetam potent phenolics which might provide a rich and novel source of natural antioxidants as food additives replacing synthetic ones in food industry.