Interspecific variability of antioxidant activities and phenolic composition in Mesembryanthemum genus

In the present study, shoot extracts from edible halophytic Mesembryanthemum species were evaluated for their effects against O-2(radical anion), DPPH, and ABTS radicals. The reducing power, chelating ability, inhibition of lipid peroxidation and of beta-carotene bleaching were also evaluated. Moreover, the total phenolic, flavonoid, and condensed tannin contents were determined. In vitro biotests showed a significant difference in the antioxidant capacities of the species studied. Mesembryanthemum edule was found to exhibit the higher antioxidant activity, except for the iron-chelating test where M. crystallinum showed the best activity with the lowest EC50 value (2.13 mg ml(-1)). Accordingly, M. edule exhibited high phenolic levels, especially in total phenols (70 mg of gallic acid equivalents/g dry weight), while no significant difference was found between M. crystallinum and M. nodiflorum (1.4 and 1.7 mg GAE g(-1) DW, respectively). Due to its strong antioxidant activities and high levels of phenols, M. edule was further studied for its phenolic constituents. HPLC analysis revealed 12 compounds, mainly flavonoids, with phloretin, quercitrin, and avicularin as the most abundant (1, 0.84 and 0.66 mg g(-1) DW, respectively). These results evidenced the great variability in antioxidant capacities of these halophytes and suggested that M. edule might be an important source of functional phenolic compounds. (C) 2009 Elsevier Ltd. All rights reserved.