L liposomes with or without crude carotenoid extract or its fractions were subjected to oxidation by singlet oxygen generated by photo sensitisation of methylene blue, and the oxidation was monitored by increase in conjugated diene content. α-Tocopherol was used as a positive control. In case of liposomes without any sample, the conjugated diene content increased rapidly and at the end of 24 h the increase was 5.1 ± 0.8-fold, compared to the level at time zero (Fig. 3A). Compared to the control, in the liposomes containing fraction F3, the increase was marginal (1.7 ± 0.2-fold). Fraction F3 inhibited the oxidation better than the known antioxidant α-tocopherol (2.2 ± 0.1-fold). Even in crude extract the increase was lower (2.7 ± 0.3-fold) compared to fraction F1 and fraction F2. The higher antioxidant activity of fraction F3 is indicated by a higher protection factor (14.1 ± 3.2 units) compared to α-tocopherol (6.2 ± 0.1 units). Comparatively, fraction F2 showed the lowest activity (2.7 ± 0.3 units) (Fig. 3B). The in vitro assays for singlet oxygen quenching activity of extracts had indicated (Table 1) higher activity in fraction F1, followed by fraction F3, fraction F2 and CE, which is different from the observations made with liposome oxidation.