Enhanced E / Z Isomerization of (All‐ E )‐lycopene by Employing Iron(III) Chloride as a Catalyst

Abstract Catalytic isomerization of (all ‐E )‐lycopene to Z ‐isomers using iron(III) chloride was investigated and optimized under various conditions of solvents, concentrations of iron(III) chloride, and reaction temperatures. The total contents of Z ‐isomers converted were higher in the order of CH 2 Cl 2 (78.4%) > benzene (61.4%) > acetone (51.5%) > ethyl acetate (50.8%) at 20 °C for 3 h using 1.0 × 10 −3 mg/mL iron(III) chloride for 0.1 mg/mL (all‐ E )‐lycopene. However, the decomposition of lycopene was markedly accelerated in CH 2 Cl 2 : the remaining lycopene after the reaction for 3 h and 12 h was only 79.4% and 47.5%, respectively. As the concentration of catalyst increased in acetone, the Z ‐isomerization ratio of lycopene increased to more than 80%, followed by rapid degradation of lycopene to undetectable levels using >4.0 × 10 −3 mg/mL iron(III) chloride with the above concentration of (all‐ E )‐lycopene. Finally, greater isomerization (79.9%) was attained at 60 °C in acetone for 3 h in the presence of 1.0 × 10 −3 mg/mL iron(III) chloride, largely without decomposition of lycopene (remaining ratio of total amount of lycopene isomers after the reaction, 96.5%). As iron(III) chloride has found general use as a food additive for iron fortification and acetone is also widely used in the food field, this method can be applied to the food and beverage processing industry.