Solvent effects on Antioxidants and biological activities of the halophyte Nitraria retusa (Forssk.) Asch

Abstract

Nitraria retusa (Forssk.) Asch. is a traditional medicinal species widely used as anti-inflammatory and cicatrizing agent. In this work, two fractions (non-polar and polar) of Nitraria leaves, after fractionation by solvent mixture (chloroform/methanol/water, 12/5/3), were investigated on their phenolic content, antioxidant activity (using several tests) and antimicrobial capacity against human pathogen strains. Moreover, phenolic and fatty acid compositions were identified using RP-HPLC and GC/MS, respectively. Results showed that phenolic contents and antioxidant activities varied considerably as function of solvent polarity. Polar fraction leaves (methanol/water) showed the highest polyphenol (7.97mg GAE/g DW) and tannin (1.78mg CE/g DW) contents, while chloroform fraction (non-polar) exhibits the highest content of flavonoids (2.74mg CE/g DW). Moreover, antiradical activity against DPPH, and β-carotene bleaching test (IC50 values were 39, 700µg.ml-1, respectively) and Fe-reducing power (EC50=410µg ml-1) were more important in leaf non-polar fraction as compared to polar fraction. Besides, chloroform fraction was more efficient against all human pathogen strains mainly Escherichia coli and Staphylococcus aureus. The HPLC analysis showed two major phenolic compounds: trans-4-hydroxy-3-methoxycinnamic acid (ferulic acid) and p-coumaric acid. The major fatty acids identified by GC/MS were palmitic acid (28.04%), and polyunsaturated acids (48.78%) are characterized by linolenic acid (29.69%) and α-linolenic acid (omega 3) (19.09%). These results indicate that selective extraction of bioactive molecules from natural sources as halophyte species, by appropriate solvents, is important for obtaining fractions with high biological activities which can be used as preservative ingredients in food, cosmetic and/or pharmaceutical industries.