En. Frankel et al., ANTIOXIDANT ACTIVITY OF GREEN TEAS IN DIFFERENT LIPID SYSTEMS, Journal of the American Oil Chemists' Society, 74(10), 1997, pp. 1309-1315
Different commercial green teas from Japan, China, and India, were com
pared in different lipid systems. Green teas were active antioxidants
in bulk corn oil oxidized at 50 degrees C but were prooxidant in the c
orresponding oil-in-water emulsions. Green teas also were active antio
xidants in soybean lecithin liposomes oxidized at 37 degrees C in the
presence of cupric acetate as catalyst. At 50 degrees C, however, thre
e of the samples of green tea were active antioxidants in the absence
of copper catalyst, and two samples showed prooxidant activity in the
presence of copper catalyst. The marked variation in activity among gr
een tea samples may be due partly to differences in their relative par
tition between phases in different lipid systems. The improved antioxi
dant activity observed for green teas in lecithin liposomes compared t
o corn oil emulsions can be explained by the greater affinity of the p
olar tea catechin gallates for the polar surface of the lecithin bilay
ers, thus affording better protection against oxidation. Liposomes may
thus be appropriate lipid models to evaluate antioxidants for foods c
ontaining phospholipids.