Abstract: Lycopene trans-isomer undergoes geometrical isomerization into cis-isomers with thermal treatment. Influences of three isomerization method including ethyl acetate reflux, microwave assisted reflux and ultrasound/microwave assisted reflux were investigated. The results showed that proportion of cis-isomers in 6% oleoresin samples were higher than that in 90% lycopene samples after ethyl acetate reflux. Nitrogen had insignificant effects on the isomerization of lycopene. Although microwave and ultrasound-microwave assisted reflux had no significant difference with each other, both showed significance influence over refluxing in ethyl acetate reflux, proportion of cis-isomers reached more than 54% after 5 h procession. Consequently, microwave was the best way to isomerization of lycopene.

Key words: lycopene, cis-isomers, isomerization, microwave, ultrasound-microwave