Carotenoids are considered to be involved in the radioresistant mechanisms of radioresistant bacteria. In these bacterial cells, carotenoids are present in biological lipids, and therefore may be related to the radiation-induced damage of lipids. However, only limited data are available for the role of carotenoids in such damage. In this study, we irradiated an alpha-linolenic acid-benzene solution with gamma rays and analyzed the resulting oxidative degradation and peroxidation damage in the presence or absence of two typical carotenoids: beta-carotene and astaxanthin. The analyses revealed that oxidative degradation and peroxidation of alpha-linolenic acid, as evaluated by the amount of malondialdehyde and conjugated diene formed, respectively, increased in a dose-dependent manner. Moreover, 8.5 x 10(-3) M beta-carotene inhibited gamma radiation-induced oxidative degradation of cc-linolenic acid, whereas 5.0 x 10(-5) and 5.0 x 10(-6) M beta-carotene, and 5.0 x 10(-7) and 5.0 x 10(-3) M astaxanthin promoted degradation. In contrast, neither beta-carotene nor astaxanthin affected peroxidation of alpha-linolenic acid. These results suggest that an optimum concentration of carotenoids in radioresistant bacteria protects biological lipid structures from radiation-induced damage. (C) 2014 Elsevier Ltd. All rights reserved.