Chromatographic performance on a C30-bonded stationary phase of monohydroxycarotenoids with variable chain length or degree of desaturation and of lycopene isomers synthesized by various carotene desaturases

Suitability of stationary phase for LC analysis of biomolecules

Biologically active compounds such as carotenoids/isoprenoids, vitamins, steroids, saponins, sugars, long chain fatty acids, and amino acids play a very important role in coordinating functions in living organisms. Determination of those substances is indispensable in advanced biological sciences. Engineered stationary phase in LC for the analysis of biomolecules has become easier with the development of chromatographic science. In general, C₁₈ column is being used for routine analysis but specific columns are being used for specific molecule. Monolithic columns are found to have higher efficiency than normal column. Among recent introduction, triacontyl stationary phases, designed for the separation of carotenoid isomers, are widely used for the estimation of carotenoids. In comparison to conventional C₁₈ phases, C₃₀ phases exhibited superior shape selectivity for the separation of isomers of carotenoids. It is also found useful for better elution and analysis of tocopherols, vitamin K, sterols, and fatty acids. Vitamin K, E, and their isomers are also successfully resoluted and analyzed by using C₃₀ column. Amino bonded phase column is specifically used for better elution of sugars, whereas phenyl columns are suitable for the separation and analysis of curcuminoids and taxol. Like triacontyl stationary phase, pentafluorophenyl columns are also used for the separation and analysis of carotenoids. Similarly, HILIC column are best suited for sugar analysis. All the stationary phases are made possible to resolute and analyze the target biomolecules better, which are the future of liquid chromatography. The present article focuses on the differential interaction between stationary phase and target biomolecules. The applicability of these stationary phases are reported in different matrices.

Guide for Carotenoid Identification in Biological Samples

In recent years there has been considerable interest in carotenoids with respect to their biological roles in animals, microorganisms, and plants, in addition to their use in the chemical, cosmetics, food, pharmaceutical, poultry, and other industries. However, the structural diversity, the different range of concentration, and the presence of cis/trans-isomers complicate the identification of carotenoids. This review provides updated information on their physical and chemical properties as well as spectroscopic and chromatographic data for the unambiguous determination of carotenoids in biological samples.

Photoinduced isomerization of lycopene and application to tomato cultivation

The present study aimed to investigate if growth conditions have an impact on the isomeric composition of lycopene in tomatoes. First a model system for photoinduced isomerization was established. Tomato extracts were irradiated with a halogen lamp, whose wavelength spectrum is close to the spectrum of daylight and thus mimics field-grown cultivation. Different optical filters were interposed between lamp and samples to simulate greenhouse conditions. 5-cis-Lycopene was formed preferentially while the concentration of 7-cis-lycopene decreased in field-grown model systems. The change of isomerization in greenhouse model systems led to a significantly different ratio. Consequently 5-cis- and 7-cis-lycopene were identified as potent markers for the differentiation of various lighting conditions during cultivation. This result was verified in biological samples. Authentic field-grown tomatoes (var. Lycopersicon esculentum Mill. var. commune L. H. Bailey "Harzfeuer") showed a significantly higher content of 5-cis-lycopene 5.90 ± 0.45% compared to tomatoes of the same variety grown under electric lighting 4.11 ± 0.10%. Additionally, the ratio of 7-cis-lycopene was significantly lower under field-grown conditions.

The impact of industrial processing on health-beneficial tomato microconstituents

The effect of industrial processing was investigated on the stability of tomato carotenoids, phenolic compounds and ascorbic acid. A deep insight in the processed products allowed the quantification of caffeic acid hexosides, which are far more important contributors than the well-known chlorogenic acid, dicaffeoylquinic acids and quercetin oligosaccharides (new feruloyl, sinapoyl and syringoyl derivatives of quercetin apiosylrhamnosylglucoside). (E)-β-Carotene and (E)-lycopene were also quantified along with different mono- and di-(Z)-isomers of lycopene which were tentatively assigned. Processing of fresh tomato into paste had an overall positive effect on the contents in phenolic compounds, no effect on lycopene and a slight and high detrimental effect on β-carotene and ascorbic acid, respectively. The balance between the increase in tomato matrix extractability and microconstituent catabolism was further observed in two contrasted transformations of paste into sauce. Overall, the nutritional quality of tomato-processed products, except for ascorbic acid, is mainly preserved through manufacture.

Cloning and functional characterization of the maize carotenoid isomerase and β-carotene hydroxylase genes and their regulation during endosperm maturation

In order to gain further insight into the partly-characterized carotenoid biosynthetic pathway in corn (Zea mays L.), we cloned cDNAs encoding the enzymes carotenoid isomerase (CRTISO) and β-carotene hydroxylase (BCH) using endosperm mRNA isolated from inbred line B73. For both enzymes, two distinct cDNAs were identified mapping to different chromosomes. The two crtiso cDNAs (Zmcrtiso1 and Zmcrtiso2) mapped to unlinked genes each containing 12 introns, a feature conserved among all crtiso genes studied thus far. ZmCRTISO1 was able to convert tetra-cis prolycopene to all-trans lycopene but could not isomerize the 15-cis double bond of 9,15,9'-tri-cis-ζ-carotene. ZmCRTISO2 is inactivated by a premature termination codon in B73 corn, but importantly the mutation is absent in other corn cultivars and the active enzyme showed the same activity as ZmCRTISO1. The two bch cDNAs (Zmbch1 and Zmbch2) mapped to unlinked genes each coding sequences containing five introns. ZmBCH1 was able to convert β-carotene into β-cryptoxanthin and zeaxanthin, but ZmBCH2 was able to form β-cryptoxanthin alone and had a lower overall activity than ZmBCH1. All four genes were expressed during endosperm development, with mRNA levels rising in line with carotenoid accumulation (especially zeaxanthin and lutein) until 25 DAP. Thereafter, expression declined for three of the genes, with only Zmcrtiso2 mRNA levels maintained by 30 DAP. We discuss the impact of paralogs with different expression profiles and functions on the regulation of carotenoid synthesis in corn.

Carotenoids and carotenogenic genes in Podospora anserina: engineering of the carotenoid composition extends the life span of the mycelium

Carotenoids have been identified in the fungus Podospora anserina and a parallel pathway to neurosporene and beta-carotene was established. Three genes for the beta-carotene branch have been cloned and their function elucidated. They correspond to the al-1, al-2 and al-3 genes from Neurospora crassa. They were individually and in combinations over-expressed in P. anserina in order to modify the carotenoid composition qualitatively and quantitatively. In the resulting transformants, carotenoid synthesis was up to eightfold increased and several intermediates of the pathway together with special cyclic carotenoids, beta-zeacarotene and 7,8-dihydro-beta-carotene, accumulated. All transformants with an over-expressed al-2 gene (encoding a phytoene synthase and a lycopene cyclase) displayed up to 31% prolonged life span.

Evolution of carotene desaturation: the complication of a simple pathway

In a series of desaturation reactions, the trienoic structures of phytoene and diapophytoene are extended to a maximum of 15 or 11 conjugated double bonds, respectively. After the cloning of several genes from bacteria and eukaryotes, the desaturation reactions were first analyzed in a heterologous host by functional genetic complementation. In addition, different desaturases were heterologously expressed and the reactions studied in vitro. This revealed that in archaea, non-photosynthetic prokaryotes and fungi the desaturases differ significantly from convergently evolved desaturases in cyanobacteria, Chlorobaculum (old name Chlorobium) species and eukaryotic photosynthetic organisms including plants. Detailed analysis of the desaturation reactions including the determination of the substrates converted by the enzymes, the intermediates and the products formed in the reactions revealed the bacterial all-trans desaturation pathway catalyzed by a single enzyme and the cyanobacterial/plant type poly-cis desaturation pathway which involves two closely related desaturases. This indicates that in the course of evolution of carotenogenesis from bacteria via cyanobacteria to plants, the simple situation of one enzyme for the entire reaction sequence from phytoene to all-trans lycopene changed to a more complex process. Three individual enzymes, newly acquired phytoene and zeta-carotene desaturases, as well as a carotene isomerase which is phylogenetically related to CrtI are involved. Only the CrtI-type enzymes seem to have the property to catalyze cis to trans conversion of carotenes.

Impact of the stage of ripening and dietary fat on in vitro bioaccessibility of beta-carotene in 'Ataulfo' mango

Pulp from "slightly ripe", "moderately ripe", or "fully ripe" mangoes was digested in vitro in the absence and presence of processed chicken as a source of exogenous fat and protein to examine the impact of stage of ripening of mango on micellarization during digestion and intestinal cell uptake (i.e., bioaccessibility) of beta-carotene. The quantity of beta-carotene transferred to the micelle fraction during simulated digestion significantly increased as the fruit ripened and when chicken was mixed with mango before digestion. Qualitative and quantitative changes that occur in pectin from mango pulp during the ripening process influenced the efficiency of micellarization of beta-carotene. Finally, the uptake of beta-carotene in micelles generated during simulated digestion by Caco-2 human intestinal cells confirmed the bioaccessibility of the provitamin A carotenoid in mango.

Identification and quantification of xanthophyll esters, carotenes, and tocopherols in the fruit of seven Mexican mango cultivars by liquid chromatography-atmospheric pressure chemical ionization-time-of-flight mass spectrometry [LC-(APcI(+))-MS]

A liquid chromatography-mass spectrometry (LC-MS) method was developed to simultaneously identify and quantify carotenoids and tocopherols in the fruit of seven mango cultivars grown in Mexico. Fruit maturity was characterized objectively, and carotenoids and tocopherols were isolated by solvent extraction and analyzed by HPLC coupled to a C30 stationary phase and diode array, fluorescence, and mass (time-of-flight) detectors. All cultivars had a similar carotenoid pattern, in which all-trans-beta-carotene and dibutyrates of all-trans-violaxanthin and 9-cis-violaxanthin were the most abundant. The content of all-trans-beta-carotene ranged between 0.4 and 2.8 mg/100 g, and 'Haden' and 'Ataulfo' mangoes had the highest amount. The amounts of all-trans-violaxanthin and 9-cis-violaxanthin (as dibutyrates) ranged between 0.5 and 2.8 mg/100g and between 0.4 and 2.0 mg/100 g, respectively. The content of alpha-tocopherol was low (200-500 microg/100 g). The results of this study indicate that all-trans-beta-carotene, all-trans-violaxanthin, and 9-cis-violaxanthin are the most abundant carotenoids in mango grown in Mexico.

Cooperation of two carotene desaturases in the production of lycopene in Myxococcus xanthus

In Myxococcus xanthus, all known carotenogenic genes are grouped together in the gene cluster carB-carA, except for one, crtIb (previously named carC). We show here that the first three genes of the carB operon, crtE, crtIa, and crtB, encode a geranygeranyl synthase, a phytoene desaturase, and a phytoene synthase, respectively. We demonstrate also that CrtIa possesses cis-to-trans isomerase activity, and is able to dehydrogenate phytoene, producing phytofluene and zeta-carotene. Unlike the majority of CrtI-type phytoene desaturases, CrtIa is unable to perform the four dehydrogenation events involved in converting phytoene to lycopene. CrtIb, on the other hand, is incapable of dehydrogenating phytoene and lacks cis-to-trans isomerase activity. However, the presence of both CrtIa and CrtIb allows the completion of the four desaturation steps that convert phytoene to lycopene. Therefore, we report a unique mechanism where two distinct CrtI-type desaturases cooperate to carry out the four desaturation steps required for lycopene formation. In addition, we show that there is a difference in substrate recognition between the two desaturases; CrtIa dehydrogenates carotenes in the cis conformation, whereas CrtIb dehydrogenates carotenes in the trans conformation.

A small-scale method for quantitation of carotenoids in bacteria and yeasts

Microbial carotenoids are difficult to extract because of their embedding into a compact matrix and prominent sensitivity to degradation. Especially for carotenoid analysis of bacteria and yeasts, there is lack of information about capability, precision and recovery of the method used. Accordingly, we investigated feasibility, throughput and validity of a new small-scale method using Micrococcus luteus and Rhodotorula glutinis for testing purposes. For disintegration and extraction, we combined primarily mild techniques: enzymatically we used combinations of lysozyme and lipase for bacteria as well as lyticase and lipase for yeasts. Additional mechanical treatment included sonication and freeze-thawing cycles. Chemical treatment with dimethylsulfoxide was applied for yeasts only. For extraction we used a methanol-chloroform mixture stabilized efficiently with butylated hydroxytoluene and alpha-tocopherol. Separation of compounds was achieved with HPLC, applying a binary methanol/tert-butyl methyl ether gradient on a polymer reversed C30 phase. Substances of interest were detected and identified applying a photodiode-array (PDA) and carotenoids quantitated as all-trans-beta-carotene equivalents. For evaluation of recovery and reproducibility of the extraction method, we used beta-8'-apo-carotenal as internal standard. The method provides a sensitive tool for the determination of carotenoids from bacteria and yeasts and also for small changes in carotenoid spectrum of a single species. Corequisite large experiments are facilitated by the high throughput of the method.

Identification of isolutein (lutein epoxide) as cis-antheraxanthin in orange juice

The carotenoid profile of orange juice is very complex, a common characteristic for citrus products in general. This fact, along with the inherent acidity of the product, which promotes the isomerization of some carotenoids, makes the correct identification of some of these pigments quite difficult. Thus, one of the carotenoids occurring in orange juice has been traditionally identified as isolutein, a term used to refer to lutein epoxide, although enough evidence to support that identification has not been given. In this study, the carotenoid previously identified as isolutein/lutein epoxide in orange juice has been isolated and identified as a 9 or 9'-cis isomer of antheraxanthin as a result of different tests. To support this identification, a mixture of geometrical isomers of lutein epoxide isolated from petals of dandelions was analyzed under the same conditions used for orange juice carotenoids to check that neither their retention times nor their spectroscopic features matched with those of the orange juice carotenoid now identified as a cis isomer of antheraxanthin.

Carotenoid biosynthesis in Gloeobacter violaceus PCC4721 involves a single crtI-type phytoene desaturase instead of typical cyanobacterial enzymes

Gloeobacter violaceus is a cyanobacterium isolated from other groups by lack of thylakoids and unique structural features of its photosynthetic protein complexes. Carotenoid biosynthesis has been investigated with respect to the carotenoids formed and the genes and enzymes involved. Carotenoid analysis identified ss-carotene as major carotenoid and echinenone as a minor component. This composition is quite unique and the cellular amounts are up to 10-fold lower than in other unicellular cyanobacteria. Carotenoid biosynthesis is up-regulated in a light-dependent manner. This enhanced biosynthesis partially compensates for photooxidation especially of ss-carotene. The sequenced genome of G. violaceus was analyzed and several gene candidates homologous to carotenogenic genes from other organisms obtained. Functional expression of all candidates and complementation in Escherichia coli led to the identification of all genes involved in the biosynthesis of the G. violaceus carotenoids with the exception of the lycopene cyclase gene. An additional diketolase gene was found that functioned in E. coli but is silent in G. violaceus cells. The biggest difference from all other cyanobacteria is the existence of a single bacterial-type 4-step desaturase instead of the poly cis cyanobacterial desaturation pathway catalyzed by two cyanobacterial-type desaturases and an isomerase. The genes for these three enzymes are absent in G. violaceus.

Identification of zeinoxanthin in orange juices

The monohydroxycarotenoid fraction of orange juice has been isolated by TLC and studied to determine whether the carotenoid accompanying beta-cryptoxanthin was alpha-cryptoxanthin or zeinoxanthin. The provitamin A carotenoid alpha-cryptoxanthin has been widely reported in orange juice, although its identification has been carried out mainly on the basis of its spectral features, which are virtually identical with those of its non-provitamin A isomer, zeinoxanthin. As a result of a study of the UV-vis and mass spectra of the monohydroxycarotenoid fraction and of the methylation test, it was concluded that the carotenoid accompanying beta-cryptoxanthin was the non-provitamin A carotenoid zeinoxanthin.

zeta-Carotene cis isomers as products and substrates in the plant poly-cis carotenoid biosynthetic pathway to lycopene

The plant carotenoid biosynthetic pathway to cyclic carotenes proceeds via carotene precursors in cis configuration. Involvement of individual isomers was elucidated by genetic complementation of desaturations and in vitro reactions of the corresponding enzyme. Determination of substrate and product specificity of phytoene and zeta-carotene desaturase revealed that 15-cis-phytoene is converted to 9,15,9'-tricis-zeta-carotene with 15,9'-dicis-phytofluene as intermediate by the first desaturase. Prior to a subsequent conversion by zeta-carotene desaturase, the 15-cis double bond of 9,15,9'-tricis-zeta-carotene has to be (photo)isomerized to all-trans. Then, the resulting 9,9'-dicis-zeta-carotene is utilized by zeta-carotene desaturase via 7,9,9'-tricis-neurosporene to 7,9,7',9'-tetracis-lycopene. Other zeta-carotene isomers that are assumed to be spontaneous isomerization products were not converted, except for the asymmetric 9-cis-zeta-carotene. This isomer is desaturated only to 7,9-dicis-neurosporene resembling a dead-end of the pathway. Prolycopene, the product of the desaturation reactions, is finally isomerized by a specific isomerase to all-trans-lycopene, which is a prerequisite for cyclization to beta-carotene. The 5-cis-lycopene and the 9-cis-and 13-cis-beta-carotene isomers detected in leaves are thought to originate independently from cis precursors by non-enzymatic isomerization of their all-trans forms.

Slr1293 in Synechocystis sp. strain PCC 6803 Is the C-3',4' desaturase (CrtD) involved in myxoxanthophyll biosynthesis

When grown at high light intensity, more than a quarter of the total carotenoids in the unicellular cyanobacterium Synechocystis consists of myxoxanthophyll, a polar carotenoid glycoside. The biosynthetic pathway of myxoxanthophyll is unknown but is presumed to involve a number of enzymes, including a C-3',4' desaturase required to add one double bond to generate 11 conjugated double bonds in the monocyclic myxoxanthophyll. A candidate for this desaturase is Slr1293, which was identified by genome similarity searching. To determine whether Slr1293 is a desaturase recognizing neurosporene and lycopene, slr1293 was expressed in Escherichia coli strains accumulating neurosporene or lycopene. Confirming such a desaturase function for Slr1293, these E. coli strains accumulated 3',4'-didehydroneurosporene and 3',4'-didehydrolycopene, respectively. Indeed, deletion of slr1293 in Synechocystis provides further evidence that Slr1293 is a desaturase recognizing neurosporene: In the slr1293 deletion mutant, neurosporene was found to accumulate and was further processed to produce neurosporene glycoside. Neurosporene hereby becomes a primary candidate to be the branch point molecule between carotene and myxoxanthophyll biosynthesis in this cyanobacterium. The slr1293 gene was concluded to encode a C-3',4' desaturase that is essential for myxoxanthophyll biosynthesis, and thus it was designated as crtD. Furthermore, as Slr1293 appears to recognize neurosporene and to catalyze the first committed step on the myxoxanthophyll biosynthesis pathway, Slr1293 plays a pivotal role in directing a portion of the precursor pool for carotenoid biosynthesis toward myxoxanthophyll biosynthesis in Synechocystis sp. strain PCC 6803.

A novel type of lycopene epsilon-cyclase in the marine cyanobacterium Prochlorococcus marinus MED4

Chlorophyll- b-possessing cyanobacteria of the genus Prochlorococcus share the presence of high amounts of alpha- and beta-carotenoids with green algae and higher plants. The branch point in carotenoid biosynthesis is the cyclization of lycopene, for which in higher plants two distinct enzymes are required, epsilon- and beta-lycopene cyclase. All cyanobacteria studied so far possess a single beta-cyclase. Here, two different Prochlorococcus sp. MED4 genes were functionally identified by heterologous gene complementation in Escherichia coli to encode lycopene cyclases. Whereas one is both functionally and in sequence highly similar to the beta-cyclase of Synechococcus sp. strain PCC 7942 and other cyanobacteria, the other showed several intriguing features. It acts as a bifunctional enzyme catalyzing the formation of epsilon- as well as of beta-ionone end groups. Expression of this cyclase in E. coli resulted in the simultaneous accumulation of alpha- beta-, delta-, and epsilon-carotene. Such an activity is in contrast to all lycopene epsilon-cyclases known so far, including those of the higher plants. Thus, for the first time among prokaryotes, two individual enzymes were identified in one organism that are responsible for the formation of cyclic carotenoids with either beta- or epsilon-end groups. These two genes are suggested to be designated as crtL-b and crtL-e. The results indicate that both enzymes might have originated from duplication of a single gene. Consequently, we suggest that multiple gene duplications followed by functional diversification resulted several times, and in independent lineages, in the appearance of enzymes for the biosynthesis of cyclic carotenoids.