Occurrence of carotenoid cis-isomers in food: Technological, analytical, and nutritional implications

Carotenoids are important plant pigments and, therefore, constitute also part of the human diet. They predominantly occur in their all-trans configuration, however, processing may lead to the formation of cis-isomers which possess different biological properties such as decreased provitamin A activity, and altered bioavailability and antioxidant capacity. The objective of this contribution is to review the effects of processing on trans-cis-isomerization, with particular attention to beta-carotene, lycopene, lutein, and zeaxanthin as the most widespread and important carotenoids. Furthermore, aspects of carotenoid isomer analysis and bioavailability are also included in this treatise.