RAPID ISOMERIZATION AND STORAGE STABILITY OF LYCOPENE

The objective of this work was to prepare a stable lycopene mixture with higher bioavailability, i.e., lycopene with higher ratio of Z-isomers. Isomerization of lycopene was studied in organic solvents. Refluxing all-E lycopene in ethyl acetate with or without microwave assistant to isomerize lycopene, then, separate the all-E lycopene from the mixture by low-temperature crystallization to increase the ratio of Z-isomers. The ratio of Z-lycopene could reach 37.3% after refluxing all-E lycopene in ethyl acetate for 10-12 h. Microwave-assisted refluxing in ethyl acetate improved the conversion rate and content of Z-isomers, 5-Z and 9-Z especially. The processing times to reach equilibrium in ethyl lactate were 120, 25, 15 and 5 min at the temperatures of 90, 110, 130 and 150°C respectively. By using low-temperature freezing crystallization technology (-18°C) for 24 h and suitable separation, the ratio of Z-isomers was increased to 78-85%. The stability test of lycopene showed that retro-isomerization occurred in lycopene isomers with 13Z-lycopene being the least stable. The developed technology works more efficiently than existing methods of lycopene isomerization. These findings are very important for Z-lycopene commercialization and the product with higher ratio of Z-lycopene can be widely used in the functional food industry.