In Vitro and in Vivo Bioavailability of Carotenoids and Tocopherols from Fruits and Vegetables: A Complementary Approach

Bioavailability is a critical feature in the assessment of the role of micronutrients in human health, and the approaches to this issue include in vitro and in vivo methods. Foodand host-related factors affect the bioavailability of carotenoids and tocopherols, and major challenges in the study of bioavailability include the release of these compounds from the food matrix, micellization, the measurement of the plasma response and the inter-individual variability. To evaluate bioaccessibility, in vitro gastrointestinal models have been used to assess stability, hydrolysis of carotenol esters and transfer efficiency of carotenoids (i.e. -cryptoxanthin, lutein, -carotene, lycopene) and tocopherols (i.e. and -tocopherol) from fruits and vegetables. In vivo (human) bioavailability has been studied mostly by assessing the responses in chylomicron fractions and serum produced by different dietary intervention protocols. Available in vitro data show that the stability of carotenoids and tocopherols is high, although micellization is a critical determinant of the bioaccessibility. In human studies, upon dietary intervention, changes in serum concentrations may be observed for some compounds (i.e. -cryptoxanthin, lutein, -tocopherol), but not for others ( -tocopherol, -carotene). Overall, the behaviour of these phytochemicals under in vitro gastrointestinal conditions does not fully explain the changes observed in in vivo studies. The results indicate that in vitro methods are useful for assessing food-related factors affecting bioavailability, although host-related factors, physiological processes and methodological constraints may limit the comparability and the “predictive value” of in vitro models. In this respect, the two approaches should be considered complementary, but not necessarily interchangeable. _____________________________________________________________________________________________________________