ANTIOXIDANT AND PROOXIDANT ACTIVITIES OF THE BROWN-ALGAE, LAMINARIA-DIGITATA, HIMANTHALIA-ELONGATA, FUCUS-VESICULOSUS, FUCUS-SERRATUS AND ASCOPHYLLUM-NODOSUM

The ability of Laminaria digitata, Himanthalia elongnta, Fucus vesicul osus, Fucus serratus and Ascophyllum nodosum to scavenge peroxyl radic als was investigated by kinetic studies in a model system. The thermal initiated oxidation of methyl linoleate was performed at 60 degrees C in heptanol, with or without antioxidants. When they reached 1% of th e substrate, seaweed extracts exhibited antioxidant activities by exte nding the induction period, but they did not suppress the rate of oxyg en uptake as did vitamin E. A synergistic effect occurred when both al gal extracts (1.5 g L-1) and vitamin E (0.4 mmol L-1) were present, an d the effectiveness of the combined antioxidants during the whole indu ction period was vitamin E effectiveness. The synergistic effect of L. digitata, however, was subject to seasonal variations: samples collec ted in summer were effective synergists, whereas samples collected in winter displayed a marked negative synergism. The phospholipid fractio ns of F. vesiculosus, F. serratus and A. nodosum, including pigments, accounted for only 6% of the total lipid fraction, and did not exhibit a large synergistic effect. The main phospholipid was not phosphatidy l ethanolamine as usually related, but phosphatidyl inositol. Fucoxant hin had some antioxidant activity per se under our experimental condit ions, but did not act as a synergist of vitamin E. The most potent syn ergists were recognized as chlorophyll a and related compounds by the application of liquid-liquid partition and chromatography for the iden tification of active components.