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

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 CH₂Cl₂ (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 CH₂Cl₂: 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.