Lycopene has a large number of geometric isomers caused by E/Z isomerization at arbitrary sites within the 11 conjugated double bonds, offering varying characteristics related to features such as antioxidant capacity and bioavailability. However, the geometric structures of only a few lycopene Z-isomers have been thoroughly identified from natural sources. In this study, seven multi-Z-isomers of lycopene, (9Z,13'Z)-, (5Z,13Z,9'Z)-, (9Z,9'Z)-, (5Z,13'Z)-, (5Z,9'Z)-, (5Z,9Z,5'Z)-, and (5Z,9Z)-lycopene, were obtained from tomato samples by thermal isomerization, and then isolated by elaborate chromatography, and fully assigned using proton nuclear magnetic resonance. Moreover, the theoretically preferred pathway from (all-E)-lycopene to di-Z-isomers was examined with a computational approach using a Gaussian program. Fine-tuning of the HPLC separation conditions led to the discovery of novel multi-Z-isomers, and whose formation was supported by advanced theoretical calculations.

Since Z‐isomers of lycopene are more bioavailable and show a higher antioxidant capacity than the (all‐E)‐isomer, it is important to investigate foods containing high amount of the Z‐isomer and develop practically feasible method for Z‐isomerization of (all‐E)‐lycopene. First, we investigated the E/Z isomer ratio of lycopene in raw and commercially available processed tomato products using an improved normal‐phase HPLC method. The tomato products contained 4.6–33.4% of Z‐isomers to the total lycopene, (5Z)‐lycopene being the most abundant Z‐isomer. The oil‐containing products like tomato sauce and tomato soup suffered heat processing contained a higher percentage of Z‐isomers of lycopene (27.4–33.4%). Subsequently, the impact of the amount and types of oils added on thermal Z‐isomerization of (all‐E)‐lycopene contained in tomato puree was investigated. Increased addition of olive oil to tomato puree increased the production of lycopene Z‐isomers upon heating at 120°C. (all‐E)‐Lycopene contained in tomato puree was converted to Z‐isomers in the range of 39.2–50.7%, when 5% of vegetable oil (linseed, soybean, corn, sesame, rapeseed, rice bran, safflower seed, olive, sunflower seed, or coconut oils) or animal fat (beef tallow and pork lard) was added before heating at 120°C for 30 min. When sesame oil was employed, the total Z‐isomerization ratio and (5Z)‐lycopene content were significantly increased. Practical applications: The dietary intake of lycopene offers many health benefits such as decreased risk of cancer and arteriosclerosis. Lycopene has a large number of geometric isomers caused by E/Z isomerization at arbitrary sites within the eleven conjugated double bonds, and the functionalities such as antioxidant capacity and bioavailability of the Z‐isomers are higher than those of the all‐E‐isomer. This study clarified the foods richly containing Z‐isomers of lycopene and demonstrated thermal Z‐isomerization of (all‐E)‐lycopene contained in tomato puree with edible oils and fats. These findings will contribute to effective intake of lycopene and the development of facile isomerization of (all‐E)‐lycopene to Z‐isomers in the fields of food, drink, and dietary supplement manufacturing, as well as for daily cooking at home. The Z‐isomers of lycopene contents in processed tomato products and thermal isomerization of (all‐E)‐lycopene to the Z‐isomers with edible oils and fats were investigated. The tomato products cooked with oils contained higher levels of the Z‐isomers, and sesame oil had excellent promoting effect of thermal Z‐isomerization of (all‐E)‐lycopene.

No abstract

This study aimed to efficiently separate and concentrate lycopene Z-isomers from tomato pulp using supercritical CO 2 (SC-CO 2). The separation relies on the different solubility of (all-E)-lycopene and the Zisomers. Total lycopene recovery using SC-CO 2 at 50 °C and 30 MPa for 1 h was extremely low (1.2%). Thus, before the separation test, an optimal co-solvent was selected from water, organic chemicals, and edible vegetable oils; hazelnut oil, which had the highest lycopene recovery (21.6%), was adopted. When using hazelnut oil as a co-solvent, the extraction of lycopene Z-isomers was completed in a short time compared to (all-E)-lycopene. Furthermore, when the extraction was conducted at higher pressure (50 MPa) and temperature (80 °C), the Z-isomer content decreased due to the improvement of (all-E)-lycopene solubility. Thus, to selectively and efficiently extract lycopene Z-isomers, addition of a co-solvent, and a relatively short contact time, low pressure, and low temperature extraction were important.

Based on our findings and as supported by its long history of consumption, tomato oleoresin that contains high amounts of Z-isomers of lycopene prepared with supercritical carbon dioxide can be considered as safe for human consumption. © 2016 Society of Chemical Industry.