In unprocessed plants, usually all-trans (all E) double-bond configurations occur, but
cis isomers of each carotenoid are also possible. Processing and storage can cause
isomerization of carotenoids in foods and affect the color. The compounds with all-trans
configurations have the deepest color. Increasing the number of cis bonds results in gradual
lightening of the color. The cis isomers not only absorb less strongly than the all-trans
isomer, but they also show a so-called cis peak at 330–340 nm.