Abstract:

In this study, the antioxidant activities of methanol, ethyl acetate and hexane extracts from stalks of Rhubarb (Rheum rhabarbarum L.) were evaluated using different model systems ivitro. Free radical scavenging activities were assessed by measuring the scavenging activities of stalks different polar e xt racts separately using 2,2'-azino-bis  (3- ethylbenzothiazoline-6-sulphonic acid, hydro xyl and 1,1-diphenyl-2   picrylhydrazyl radicals.   Effect   of extracts on ferrous ions chelating ability and total antioxidant capacity were also investigated  for each  extract. In addition, total phenolic, flavonoid and flavonol content of rhubarb stalks ext racts were determined. The stalk methanol e xtract showed significantly the highest 1,1-diphenyl-2- picrylhydrazyl radical scavenging activity, followed by stalks ethylacetate extract, stalks hexane extract and  lastly,  butylated   hydroxytoluene.  Ethylacetate extract showed the highest 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) radical scavenging   activity   with   IC50   value   of 59.7±1.1 μg/mL,  fo llowed  by  butylated  hydroxytoluene  and methanol e xt ract with IC50 value of 53.1±2.2 and 47.9±1.3 μg/ mL, respectively, whereas the highest hydroxyl radical inhibition activity was found for methanol extracts with  IC50  values  of  75.1±2.9 μg/mL. The total antioxidant activity  was  the highest in methanol and ethylacetate extracts (284.1±11.6 and 237.6±10.0  μg  ascorbic  acid  equivalent  for  1 mg extract, respectively).  Methanol  and   ethylacetate extracts at concentration of 100 μg/ mL showed the highest chelating activity against ferrous ions (96.3±2.2% and 89.8±1.5%, respectively). All rhubarb stalk extracts showed pronounced antioxidant activities in a dose-dependent manner and the effects depend strongly on the solvent used for extraction. The results showed that extracts of the stalk of rhubarb exhibit antioxidant potential suggesting that Rheum rhabarbarum L. is a promising plant.

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