Far UV peaks contribute for identification of carotenoids E/Z isomers

By using iodine-catalyzed photoisomerization, and HPLC-DAD, we found that were: in the spectrum of each carotene there is a “far UV peak”, which maintains the maximum in all its E/Z isomers and this maximum it is different from E/Z isomers of other carotene. The values of these absorption maxima 294-296 nm for lycopene E/Z isomers; 266-269 nm for α-carotene E/Z isomers; 273-276 nm for β-carotene E/Z isomers; 281-283 nm for γ-carotene E/Z isomers; and 280-282 nm for γ-carotene E/Z isomers. These UV absorption peaks are highly valuable to determine which components are geometrical isomers of the same carotene, since that not only the maximum absorbance is specific for each carotene, but also the shapes of these peaks are clearly different. The utility of this “far UV peak” was tested, by identifying Z isomers in Bactris gasipaes fruit. We found that two carotenoids previously identified as all-E-δ-carotene and Z-γ-carotene, are actually Z-γ-carotene and Z-lycopene respectively.