High-efficiency lycopene isomerization with subcritical ethyl acetate in a continuous-flow reactor

Z-Isomers of lycopene exhibit greater bioavailability and potentially have higher biological activity than its predominant isomer, (all-E)-lycopene. Thus, the development of efficient and practicable isomerization methods is required. Here, we constructed a continuous-flow system for Z-isomerization of (all-E)-lycopene via subcritical ethyl acetate. Continuous high-temperature processing efficiently accelerated the Z-isomerization in a short time, but at the same time, a large amount of lycopene was degraded. To inhibit lycopene degradation, antioxidants were added to the process and the effects were studied. Moreover, in an effort to further enhance the Z-isomerization efficiency, a natural Z-isomerization-accelerating catalyst, allyl isothiocyanate (AITC), was added to the process. The results clearly showed that antioxidants, especially α-tocopherol (α-TC), inhibited the thermal degradation of lycopene, and AITC enhanced the Z-isomerization efficiency. Finally, we achieved over 80% of the total Z-isomer ratio in only 30 s, while inhibiting lycopene degradation.