Isomerization of carotenoids

In dark conditions, the spontaneous isomerization of carotenoids occurs in solution the rate is dependent on temperature, solvent, and carotenoid structure. In the case of P-carotene, 13-di-P-carotene was formed approximately three times faster than the 9-cis- isomer at room temperature and at 150°C. ... 

When the aim is isolation for identification by direct probe insertion mass spectrometry (MS), plastic materials, filter papers, and blenders should be avoided to prevent contamination during extraction and chromatography. It is also very important to avoid the cis-trans isomerization of carotenoids in solution, which is accelerated by heat, light, acids, and active surfaces. Therefore, a pure carotenoid or even a crude extract should never be stored in solution it should be kept completely dry in an inert atmosphere at low temperature. 

Foote, C. S., Y. C. Chang, and R. W. Denny. 1970. Chemistry of singlet oxygen. XI. Cis-trans isomerization of carotenoids by singlet oxygen and a probable quenching mechanism. J. Am. Chem. Soc. 92 5218-5219. 

To assess the effects of processing on the nutritional value of a plant food with respect to vitamin A activity, the various isomeric forms of provitamin A carotenoids present in both the fresh and processed states must be accurately measured. In such investigations it must be demonstrated that the analytical procedure does not itself cause trans-cis isomerization of carotenoids. 

IMS is a relatively new technique in which ions are separated based on size and shape using an electric field. IMS was utilized by Dong et ah (2010) to separate all-trans -lycopene from cw-lycopene and all-irans -(3-carotene from cw-(3-carotene. Unfortunately, the various cis isomers could not be separated from each other using IMS alone. The authors provided evidence to suggest that cis/trans isomerization of carotenoids occur in-source (ESI positive mode was used in these experiments). Because of this isomerization, it does not appear likely that IMS will replace HPLC as a means of separating geometrical isomers of carotenoids in the near future (Dong et ah, 2010). 

The use of iodine as starter for the preparation of Grignard reagents has been mentioned. Work of Zechmeister has abundantly demonstrated the efficiency of iodine as a catalyst for the cis-trans isomerization of carotenoid pigments. ... 

Jeevarajan AS, Kispert LD and Piekara-Sady L (1993b) An ENDOR study of carotenoid cation radicals on silica-alumina solid supports. Chem Phys Lett 209 269-274 Jeevarajan AS, Wei CC and Kispert LD (1994a) Geometrical isomerization of carotenoids in dichloromethane. J Chem Soc Perkin Trans 2 861-869... 

Carotenoids are chemically more stable than chlorophyll. Freezing and thawing of the food causes little change in the carotenoid content. Thermal processing has minimal effect on the carotenoid content (Boileau and Erdman, 2004 Updike and Schwartz, 2003). However, thermal treatments of food induce isomerization of carotenoids from trans to cis isomers, thereby decreas-... 

The cis-trans isomerization of carotenoids has been examined in detail by Zechmeister (1%2). This topic has also been discussed in two reviews (Wee-... 

The literature on geometrical isomerism of carotenoids from 1923 to 1970 has been discussed in detail by Zechmeister 181,182) and Weedon 174). Problems related to conformation have also been considered 174). 

The effects of temperature on carotenoid content can be considered from three perspectives (1) evaluation of stability or retention of carotenoids, (2) study of the chemical changes (isomerization, oxidation, epoxy-furanoid rearrangement), and (3) their effects on the nutritional value and other carotenoid actions in humans. The first two topics are discussed in the following sections. The third is presented in Section 3.2.4.1 of Section 3.2. 

Among thermal processes, canning caused the largest trans-to-cis isomerization of provitamin A carotenoids, increasing the total cis isomers by 39% for sweet potatoes, 33% for carrots, 19% for collards, 18% for tomatoes, and 10% for peaches 13-di-P-carotene was the isomer formed in highest amonnts. ... 

Losses of 45 to 48% in the P-carotene contents and formation of cis isomers were also verified by pasteurization of carrot juice at 110 and 120°C for 30 sec. No significant effects on trans-to-cis isomerization of a- and P-carotene isomers were observed after acidification and heating of carrot juice at 105°C for 25 sec. In addition, an increase of only 3% in the cis isomers of provitamin A carotenoids was observed after orange juice pasteurization. " ... 

Aside from isomerization, transformation of the 5,6-epoxy to the 5,8-furanoid group is a common alteration during heating treatments of carotenoids. Violaxanthin was found to be the major carotenoid in mangoes however, in commercially processed mango juice, violaxanthin was not detected while auroxanthin, not present in the... 

Scotter, M.J., Characterization of the coloured thermal degradation products of bixin from annatto and a revised mechanism for their formation, Food Chem., 53, 111, 1995. Zechmeister, L., Cis-trans isomerization and stereochemistry of carotenoids and diphenylpolyenes, Chem. Rev., 34, 267, 1944. 

The carotenoid isomerase (CRTISO) was the first isomerase associated with the desaturation steps and named at a time when Z-ISO was unknown to exist ise.ws.ieo.iei (and reviewed in references ). In vitro analysis of substrate conversion " and transcript profiling in planta associated CRTISO with the desaturation steps. Isaacson demonstrated that CRTISO is specific for the 7,9 or 7,9- cis bond configuration and is not involved in the isomerization of the l5-l5-cis double bond to the trans conformation. As recently shown, Z-ISO is required for isomerization of the 15-15 cis double bond of phytoene produced in dark-grown tissues as well as in stressed photosynthetic tissues. Therefore, desaturation of phytoene to lycopene involves a two-step desaturation by PDS, followed l5-cis isomerization by Z-ISO, and then each pair of double bonds introduced by ZDS is followed by CRT-ISO-mediated isomerization of the resulting conjugated double bond pair. 

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... 

The spontaneous isomerization of all-trans- carotenoids at room temperature is a slow process, and its rate depends on the solvent and the pigment structure. For example, the initial solutions of P-carotene in a mixture of tetrahydrofuran (THF), methanol, and acetonitrile containing ca. 95% of all -trans- and 5% of 9-cis- plus 13-co-isomers was transformed to 90% all-fra ns- p -ca rot ene and 9% of 9-cis- plus 13-cA-carotene after 24h of spontaneous isomerization at 25°C (Pesek et al. 

The photosensitized transformation of carotenoids has been studied using several sensitizer molecules, such as chlorophylls, iodine, rose bengal (RB), and methylene blue (MB) and in general terms isomerization is the major pathway of reaction. 

Zechmeister, L. 1944. Cis-trans isomerization and stereochemistry of carotenoids and diphenylpolyenes. Chem. Rev. 34 267-344. 

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