Radical scavenging and singlet oxygen quenching activity of extracts from Indian seaweeds

Free radicals and singlet oxygen are responsible
for oxidative stress related diseases and many natural
compounds are known to have antioxidant properties. In
this study, extracts from brown and red seaweeds of Indian
origin were evaluated for their ability to scavenge different
radicals and quench singlet oxygen. The crude extract in
methanol and its fractions in different solvents were evaluated
for their activity. The methanol extract and its fractions
from brown seaweed exhibited higher 2,2′-azinobis(3-ethylbenzothizoline-
6-sulfonic acid) radical scavenging activity
with more than 90% scavenging in butanol and ethyl acetate
fractions and correlated with polyphenol content. There
was a signifi cant difference (p<0.001) in hydroxyl radical
scavenging activity between different fractions of the same
seaweed. Among the crude extracts, extract from Gracilaria
corticata showed the highest (14.0%) activity. Crude extract
from brown seaweeds showed higher peroxyl radical scavenging
activity compared to red seaweeds. In fractions from
brown seaweed extracts, highest activity was observed in
ethyl acetate fraction (>88%) followed by hexane fraction
(>40 %). Ethyl acetate fraction from crude extract showed
higher inhibitory activity against hemoglobin induced linoleic
acid oxidation. Singlet oxygen quenching activity of
the crude extract from brown seaweed was lower (<13%)
compared to red seaweeds (16.4–20.5%).