Bioaccessibility, cellular uptake and transport of luteins and assessment of their antioxidant activities

A rapid method for producing 9Z- and 13'Z-isomers from all-E-lutein was developed using I-TiO2 as catalyst. In a simulated in vitro gastrointestinal digestion model, both trans-cis isomerization of all-E-lutein and cis-trans isomerization of Z-luteins occurred during the intestinal phase. The bioaccessibility of all isomers was between 14 and 23%, and it was higher for Z-luteins. In a Caco-2 cell monolayer model, all isomers were relatively stable during cellular uptake and transport across the membrane as no significant isomerization and degradation was detected, but all-E-lutein exhibited significantly higher cellular uptake and transport efficiencies. These results suggest that Z-luteins found in human plasma may likely be formed before intestinal absorption. 13'Z-Lutein also exhibited highest antioxidant activity in FRAP, DPPH and ORAC-L assays, but no significant difference in cell-based antioxidant assay compared with other isomers. Future studies on the different antioxidant activities of cis isomers of lutein in vivo will provide further explanation.