Oxidation of carotenoids

Fertile sources of carotenoids include carrots and leafy green vegetables such as spinach. Tomatoes contain significant amounts of the red carotenoid, lycopene. Although lycopene has no vitamin A activity, it is a particularly efficient antioxidant (see Antioxidants). Oxidation of carotenoids to biologically inactive xanthophyUs represents an important degradation pathway for these compounds (56). 

Interestingly, early examples of carotenoid autoxidation in the literature described the influence of lipids and other antioxidants on the autoxidation of carotenoids." " In a stndy by Budowski et al.," the influence of fat was fonnd to be prooxidant. The oxidation of carotenoids was probably not only cansed by molecnlar oxygen bnt also by lipid oxidation products. This now well-known phenomenon called co-oxidation has been stndied in lipid solntions, in aqueons solntions catalyzed by enzymes," and even in food systems in relation to carotenoid oxida-tion." The inflnence of a-tocopherol on the antoxidation of carotenoids was also stndied by Takahashi et al. ° who showed that carotene oxidation was snppressed as... 

In conclusion, oxidation of carotenoids by molecular oxygen, the so-called autoxidation process, is a complex phenomenon that is probably initiated by an external factor (radical, metal, etc.) and for which different mechanisms have been proposed. The autoxidation of a carotenoid is important to take into account when studying antioxidant activity because it can lower the apparent antioxidant activity of a carotenoid. ... 

Carotenoid oxidation products were not only formed from the parent molecules in order to elucidate structure, they were also obtained by partial or total synthesis or by direct oxidation of carotenoid precursors. Thus, apo-8 -lycopenal was synthesized in 1966 more recently, the ozonide of canthaxanthin was obtained by chemical oxidation of canthaxanthin. ... 

Perez-Galvez, A. and Minguez-Mosquera, M.I., Structure-reactivity relationship in the oxidation of carotenoid pigments of the pepper Capsicum annuum L.), J. Agric. Food Chem., 49, 4864, 2001. 

Zurcher, M. and Pfander, H., Oxidation of carotenoids II. Ozonides as products of the oxidation of canthaxanthin, Tetrahedron, 55, 2307, 1999. 

A more difficult problem to overcome is the overestimation of carotenoid concentrations in processed foods due to the usually more efficient extraction of carotenoids in such foods as a result of the denaturation of the carotenoid-protein complexes and cell damage. In addition, weight changes due to loss or gain of water or fat, enzymatic oxidation of carotenoids in raw samples, and leaching of soluble solids during processing should be considered. 

The origin of many of the components of black tea aroma has been studied. Aldehydes are produced by catechin quinone oxidation of amino acids. Enzymic oxidation of carotenoids during manufacture generates ionones and their secondary oxidation products such as theaspirone and dihydroactinidolide. Oxidation of linoleic acid is responsible for the formation of trans-2-hexenal.82... 

EPR techniques have also been used to detect and establish the structure of the carotenoid I3 complexes formed upon oxidation of carotenoids with I2 (Ding et al. 1988). At 77 K the equilibrium is shifted so that Car" , forms where n=5,7, or 9, and the polymeric l resides over the polyene chain in a n-n interaction giving rise to a detectable shift in the g-value. 

Photo-oxidation of carotenoids in Ni-MCM-41 produces an intense EPR signal (Figure 9.11) with -value 2.0027 due to the carotenoid radical another, less intense EPR signal, with =2.09 is attributed to an isolated Ni(I) species produced as a result of electron transfer from the carotenoid molecule to Ni(II). It has been reported that Ni(I) ions prepared upon reduction of Ni(II)-MCM-41 by heating in a vacuum or in dry hydrogen exhibits an EPR spectrum with , =2.09 and N=2.5... 

Jeevarajan, J. A. and L. D. Kispert (1996). Electrochemical oxidation of carotenoids containing donor/acceptor substituents. J. Electroanal. Chem. 411 57-66. 

The chemically catalyzed oxidation of carotenoids by metalloporphyrins has also been described in the literature. In 2000, French et al. described a central cleavage mimic system (ruthenium porphyrin linked to cyclodextrins) that exhibited a 15,1 S -regiosclectivity of about 40% in the oxidative cleavage of [3-carotene by tert-butyl hydroperoxide in a biphasic system (French et al. 2000). 

The literature contains other examples of the chemical oxidation of carotenoids that aim to mimic oxidation processes that potentially occur in vivo. For example, hypochlorous acid, an oxidant produced by polymorphonuclear leukocytes during inflammatory processes, was shown to oxidatively cleave [3-carotene into apocarotenals and shorter chain compounds (Sommerburg et al. 2003). 

Zurcher, M. et al. (1997). Oxidation of carotenoids-I. Dihydrooxepin derivatives as products of oxidation of canthaxanthin and beta,beta-carotene. Tet. Lett. 38(45) 7853-7856. 

Although trans to cis isomerization per se is not expected to cause major changes in color, it is the first step for intramolecular cyclization to form cyclic volatile compounds under conditions of high temperature. The oxidation of carotenoid is also required for subsequent reorganization... 

Woodall, A.A., Lee, S.W.-M., Weesie, R.J., Jackson, M.J., and Britton, G. 1997a. Oxidation of carotenoids by free radicals Relationship between structure and reactivity. Biochim. Biophys. Acta 1336 33 12. 

Moreover, carotenoid cation radicals can be formed as a result of oxidation of carotenoids by iron ions, Fe(III) (Equation 15.9) (Polyakov et al., 2001) ... 

Hurst, JS, Contreras, JE, Siems, WG, and van Kuijk, F, 2004. Oxidation of carotenoids by heat and tobacco smoke. Biofactors 20, 23-35. 

It may be supposed that cyclic y-lactones were formed by lac-tonization of acids which might represent intermediates in a bacterial or abiogenic oxidation of carotenoids into naphthenic acids. Corresponding acids were isolated from a Californian petroleum and it was assumed that they were formed by oxidation of the 3-ionone portion of 3-carotene (25) ... 

It is well established that unsatnrated fatty acids undergo oxidation, via a radical reaction mechanism. Carotenoids undergo similar reactions and indeed do this so readily they can act as antioxidants in food materials. This antioxidant ability of carotenoids derives from their ability to form a resonance stabilised free radical. In certain controlled conditions chemical oxidation of carotenoids can give rise to epoxide formation and isomerisation of this to a furanoxide (Wong,... 

Carotenoid Chemistry.—Chromic oxide oxidation of carotenoids gives extensive degradation. However, subtle control factors are present. Thus oxidation of vitamin A acid (45) gave a diketone (47), whereas its ester (46) gave a rearranged product (48). Its stereochemistry was deduced by degradation to the triol (49) which was examined by AT-ray crystallography and synthesized. Milder... 

BASF is a major producer of vitamin A, a carotenoid which is found naturally in various foods and is important for vision and for tissue growth and differentiation. Carotenoid derivatives have also been used as pharmaceuticals and as colorants for a wide variety of foods. The synthesis of vitamin A by BASF involves the Wittig coupling of an ylide and aldehyde to form the desired vitamin A product (Scheme 6.3) [34], and BASF explored variations of the Semmelhack catalyst system for the oxidation of carotenoid precursors [35]. The high copper and TEMPO loading originally reported by Semmelhack (10 mol%) were lowered to make the process more suitable for industrial scale, while mild temperatures, bubbling O2, and the use of DMF as a solvent were maintained in the modified procedure... 

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