Light exposure degrades carotenoids, and several mechanisms
of action have been proposed. Photooxidation produces
species thought to be carotenoid radical cations (Konovalova
et al., 2001; Mortensen and Skibsted, 1996). Laser flash photolysis
studies have produced evidence to suggest that rapid
bleaching of beta-carotene in some solvents like chloroform,
can occur due to light exciting the beta-carotene molecules,
which then instantly react with the solvent (chloroform in this
case) to form either a carotenoid-solvent free radical adduct or
a beta-carotene radical (due to hydrogen abstraction). The same
work has also shown that the beta-carotene molecules in the
excited state may return to ground state, where they may be attacked
by radical by-products created during the above reaction
and undergo a slower degradation process thought to possibly
form beta-carotene radical cations