Degradation of lycopene, from all trans-lycopene to cis-lycopen, by heating

Red tomatoes and red-fleshed watermelons contain a high level of lycopene with two isomers, cis- and all trans- isomers. All trans-lycopene is more valuable nutrient than cis-lycopene. A high content of cis-lycopene lowers the dietary value of fruit or the fruit - products. Individuals eat food staff with lycopene contents without awareness whether lycopene has been degraded or not. However, there is no researched information existing so far in Uganda to establish the dietary value of lycopene before and after heating. The objective of this study was to isolate all trans-lycopene and cis-lycopene and then to measure their maximum peaks of characteristic before and after degradation by heat from selected tomato and watermelon varieties from Uganda. Hexane solutions of cis-lycopene and all trans-lycopene were scanned by using UV - VIS spectroscopy. The results obtained showed that the UV - VIS absorption spectra of all trans-lycopene and cis-lycopene extracted from Citrullus lanatus has three peaks with maximum wavelengths of (503, 473 and 444 nm) and (502, 471 and 444 nm) respectively. When heated at 740C for 2 hours their maximum wavelengths were (501, 469 and 443 nm) for all trans-lycopene and (500, 469 and 444 nm) for cis-lycopene. When heated again at 740C for 2 hours their maximum wavelengths were (502, 470 and 444 nm) for both all trans-lycopene and cis-lycopene and hence lycopene has been completely degraded by heating. The absorption spectra characteristics of all trans-lycopene and cis-lycopene from tomato had three peaks with maximum wavelengths of (502, 472 and 444 nm) and (502, 471 and 444 nm) respectively. When heated at 740C for 2 hours their maximum wavelengths were (500, 469 and 443 nm) for both all trans-lycopene and cis-lycopene and hence lycopene has been completely degraded by heating. The significance of this result is that all trans-lycopene from watermelon takes longer time to be totally converted to cis-lycopene by heating rather than all trans-lycopene from tomato and hence is more stable to undergo degradation and losing its quality by heat. This gives more a preference of watermelon for dietary purpose to tomato.