Geometrical isomers of lutein and fucoxanthin: Unveiling their antioxidant potentials and skin-related biological activities

• Effects of the carotenoid isomer ratio on skin-related biological activities was studied. • Z -Isomers showed superior UV-A- and UV-B-blocking abilities than all- E -isomers. • Z -Isomer-rich carotenoids exhibit enhanced lipid peroxidation-scavenging activity. • Both isomers exhibit potent anti-elastase and anti-tyrosinase activities. • We reveal the potential of carotenoid isomers in effective skincare products. Although carotenoids are most commonly found in dietary sources as all- E -isomers, some carotenoids accumulate in the skin as Z -isomers; their roles are largely unknown. This study investigated the effects of E/Z -isomers of lutein and fucoxanthin, two xanthophyll carotenoids, on their antioxidant potential and skin-related biological activities. Evaluation of ultraviolet (UV)-blocking abilities demonstrated the superior performance of Z -isomer-rich lutein and fucoxanthin against UV-A and UV-B radiation, with Z -isomer-rich lutein exhibiting higher UV-B protection. Antioxidant assays revealed that all- E - and Z -isomer-rich lutein and fucoxanthin had potent singlet oxygen and hydroxyl radical scavenging activities. Moreover, Z -isomer-rich lutein and fucoxanthin exhibited enhanced lipid peroxidation scavenging compared with their all- E counterparts. Both isomers of lutein and fucoxanthin exhibited potent skin-antiaging and skin-whitening effects in several in vitro assays, including anti-elastase and anti-tyrosinase activities. These findings suggest that geometric isomers may enhance the therapeutic efficacy of carotenoids in skin care applications.