Antioxidant activities and RP-HPLC identification of polyphenols in the ethyl acetate extract of Tunisian Juglans regia L treated barks.

The barks and leaves of Juglans regia L. are widely used in Tunisia to maintain good oral hygiene and are known to possess high therapeutic effects. In this paper, and for the first time, we report the reversed phase-high performance liquid chromatography (RP-HPLC) identification of polyphenols in the ethyl acetate extract obtained from the barks of J. regia L.and we tested its antioxidant properties. The results showed that the ethyl acetate extract possess high antioxidant activities comparatively to the butylated hydroxytoluene (BHT) (DPPH IC50, 3 µg/ml; reducing power EC50, 99 mg.ml-1 and IC50 = 280 µg/ml for the β-carotene bleaching test). The total antioxidant activity was estimated at 329 mg GAE.g-1 DW, the total phenolic content was 33,833 mg GAE.g-1 DW and the total condensed tannin were 16.167 mg EC.g-1 DW. The RP-HPLC showed the presence of 69 compounds: 24 with a percentage ranging from 1.37 to 15.02% including the caffeic acid (15,02%), the rutin trihydrate (12.71%), the syringic acid (3.44%), the gallic acid (2.58%) and 55 compounds with a percentage varying from 0.02 to 0.93% including the chlorogenic acid (0.8%), the resorcinol (0.78%), the vanillic acid (0.77%), the naphtho-resorcinol (0.68%), the quercetin dihydrate (0.57%), the p-coumaric acid (0.56%), the  trans-cinnamic acid (0.53%) and the catechine hydrae (0.18%). In conclusion, we confirm the presence of natural compounds in the bark of Tunisian tree of J. regia with great interest, especially the polyphenols which confer to this plant a wide range of biological activities and reinforce the use of walnut bark in the developing countries in order to maintain oral hygiene.   Key words : Juglans regia, reversed phase-high performance liquid chromatography (RP-HPLC), polyphenols, antioxidant activities.