Isothiocyanate-functionalized silica as an efficient heterogeneous catalyst for carotenoid isomerization

Abstract

Daily consumption of carotenoids is associated with multiple health benefits, but their bioavailability is generally extremely low. In this context, the Z-isomerization is receiving attention as a method for increasing carotenoid bioavailability because this approach is superior to conventional physical approaches. Here we investigated the feasibility of using isothiocyanate-functionalized silica (Si-NCS) as a heterogeneous catalyst for carotenoid isomerization. We found that this catalyst promoted Z-isomerization of (all-E)-carotenoids with high efficiency, e.g., when lycopene and astaxanthin solutions were incubated at 50 °C with 10 mg/mL Si-NCS, their total Z-isomer ratios increased by approximately 80 and 50 %, respectively. Furthermore, the Z-isomerization was successfully performed continuously by introducing carotenoid solution into a column packed with Si-NCS. Materials rich in carotenoid Z-isomers have not been used in practical applications due to high production cost and quality limitations (e.g., low Z-isomer ratio). The use of Si-NCS has sufficient potential to solve both these issues.

Keywords: Astaxanthin; Continuous-flow reactor; Geometrical isomerization; Heterogeneous catalysis; Isothiocyanate group; Silica.