Model Studies on the Photosensitized Isomerization of Bixin

Abstract

The photosensitized isomerization reaction of the natural cis carotenoid bixin (methyl hydrogen 9'-cis-6, 6'-diapocarotene-6, 6'-dioate) with rose bengal or methylene blue as the sensitizer in acetonitrile/methanol (1:1) solution was studied using UV-vis spectroscopy, high-performance liquid chromatography (HPLC), and time-resolved spectroscopic techniques, such as laser-flash photolysis and singlet oxygen phosphorescence detection. In both N(2)- and air-saturated solutions, the main product formed was all-trans-bixin. The observed isomerization rate constants, k(obs), decreased in the presence of air or with increase in the bixin concentration, suggesting the participation of the excited triplet state of bixin, (3)Bix, as precursor of the cis--> trans process. On the other hand, bixin solutions in the absence of sensitizer and/or light did not degrade, indicating that the ground state of bixin is stable to thermal isomerization at room temperature. Time-resolved spectroscopic experiments confirmed the formation of the excited triplet state of bixin and its deactivation by ground state bixin and molecular oxygen quenching processes. The primary isomerization products only degraded in the presence of air and under prolonged illumination conditions, probably due to the formation of oxidation products by reaction with singlet molecular oxygen. An energy-transfer mechanism was used to explain the observed results for the bixin transformations, and the consequences for food color are discussed.

In vitro scavenging capacity of annatto seed extracts against reactive oxygen and nitrogen species

“…As expected, bixin showed lower IC 50 than all annatto extracts. Model studies on the photosensitized isomerisation of bixin show that while bixin in the ground electronic state is stable to thermal isomerization, energy transfer via photosensitization gives rise to the higher energy triplet state precursor, which readily isomerizes to the trans-isomer (Montenegro et al, 2004). Rios et al (2007) showed that bixin, is a very efficient 1 O 2 quencher in fluid solutions due to an efficient energy-transfer process, and confirmed that the triplet state energy level for bixin is lower than that of 1 O 2 (18 kcal mol À1 and 22.5 kcal mol À1 , respectively).…”

“…1), representing approximately 80% of the total carotenoids (Preston & Rickard, 1980). Besides the colorant property, bixin is known to be a very efficient quencher of singlet oxygen ( 1 O 2 ) and triplet state of sensitizers (Montenegro, Rios, Mercadante, Nazareno, & Borsarelli, 2004;Rios, Mercadante, & Borsarelli, 2007). The main phenolic compounds identified in the seeds and/or annatto extracts were hypolaetin and a caffeoyl acid derivative (Chisté, Yamashita, Gozzo & Mercadante, 2011).…”

The effects of colorifico on lipid oxidation, colour and vitamin E in raw and grilled chicken patties during frozen storage

“…The carotenoids containing more than seven conjugated double bonds are singlet oxygen quenchers (Di Mascio, Kaiser, & Sies, 1989), can deactivate the triplet excited state of sensitisers responsible for synglet oxygen formation (Montenegro, Rios, Mercadante, Nazareno, & Borsarelli, 2004), and are free radicals scavengers (Bohm, Puspitasari-Nienaber, Ferruzi, & Schwartz, 2002).…”

Characterization of different annatto extracts based on antioxidant and colour properties

“…Bixin, as almost all carotenoids, is an efficient quencher of singlet oxygen ( 1 O 2 ) (Di Mascio, Kaiser, & Sies, 1989;Montenegro, Rios, Mercadante, Nazareno, & Borsarelli, 2004) due to its triplet energy level of 18 kcal/mol being lower than the energy level of 1 O 2 (Rios, Mercadante, & Borsarelli, 2007). In addition, carotenoids are also able to quench the excited triplet state of sensitizers, which are relevant species in the oxidation of lipids, vitamins and proteins (Montenegro, Nunes, Mercadante, & Borsarelli, 2007;Montenegro et al, 2004).…”