Improving the stability of lycopene Z-isomers in isomerised tomato extracts

Abstract Tomato-based foods rich in Z -lycopene are potentially more bioavailable and have greater bioefficacy compared to natural tomato products which mainly contain all- E -lycopene. To prepare a stable tomato extract with a high level of Z -lycopene, geometrical isomerisation of lycopene was studied in organic solvents either alone or in the presence of a tomato extract. Interconversion between the isomers was observed in all systems with 13 Z -lycopene being the least stable. Heating a tomato extract containing mainly the all -E -isomer in ethyl acetate produced successively 13 Z -, 9 Z - and 5 Z -lycopene. An isomerised tomato oleoresin with a minimal content of the most unstable 13 Z -lycopene could be obtained by refluxing tomato oleoresin in ethyl acetate for 1 week. In this isomerised tomato oleoresin, total lycopene and lycopene isomer profiles were shown to remain constant for 1 year at room temperature. Accordingly, this product is a valid source of stable and potentially highly bioavailable lycopene.