Z-Isomers of lycopene and β-carotene exhibit greater skin-quality improving action than their all-E-isomers

Although most carotenoids in fruits and vegetables exist as the all-E-isomers, several carotenoids accumulated in the skin exist as the Z-isomers. However, the differences in the skin-related biological activities of the all-E- and Z-isomers are largely unknown. This study investigated the effects of E/Z-isomer ratios of lycopene and β-carotene on their ultraviolet (UV)-light-shielding ability and skin-related biological activities (i.e., antioxidant, skin anti-aging, and skin-whitening activities). Z-Isomer-rich lycopene and β-carotene were prepared by thermal isomerization of their all-E-isomers, i.e., the total Z-isomer ratios of lycopene and β-carotene were 97.7 and 89.0%, respectively. The Z-isomers exhibited higher UV-A- and UV-B-shielding abilities and greater skin-related biological activities (e.g., anti-elastase activity, hyaluronic acid production-promoting effect, anti-melanin formation activity, and inhibitory activity for melanin precursor darkening) in several assays than the all-E-isomers. These findings may contribute to understanding the significance of carotenoid Z-isomers in the skin and developing food ingredients that promote skin health.