Carotenoids continued

Thorough biochemical analysis of carotenoid biosynthesis, classical genetics, and more recently molecular genetics resulted in the elucidation of the main routes for the synthesis of acyclic and cyclic carotenoids at a molecular level (Sandmann 2001). Little is known, however, about the biosynthesis of carotenoids containing additional modifications of the end groups, the polyene chain, the methyl groups, or molecular rearrangements that contribute to the tremendous structural diversity of carotenoids. At present, hundreds of individual carotenoids have been characterized (Britton et al. 1998), and novel carotenoids continue to be isolated. All carotenoids are derived from the isoprenoid or terpenoid pathway. 

Despite the absence of clear evidence for a role in prevention of diseases, carotenoids continue to play a role in the diet of consumers and continue to be debated in the light of recent dietary trends [16]. Thus, the research on the effects of carotenoids on health should go on, as well as the efforts to provide new varieties... 

The stability of phytoene desaturase and lycopene cyclase transcripts also influenced accumulation of carotenoids. Efforts in directed evolution of carotenogenic enzymes have also continued. Alternate approaches using systematic and combinatorial gene knockout targets have allowed for enhancement of carotenoid production in the absence of a priori assumptions of regulatory mechanisms. 

It is recognized that carotenoid analysis is inherently difficult and errors can be introduced in aU steps. Thus continued efforts focusing on analytical refinements are justified so that analytical variability is not mistaken for natural variation of samples. 

The analysis of carotenoid identity, conformation, and binding in vivo should allow further progress to be made in understanding of the functions of these pigments in the photosynthetic machinery. One of the obvious steps toward improvement could be the use of continuously tuneable laser systems in order to obtain more detailed resonance Raman excitation profiles (Sashima et al 2000). This technique will be suitable for the investigation of in vivo systems with more complex carotenoid composition. In addition, this method may be applied for the determination of the energy of forbidden Sj or 2 Ag transition. This is an important parameter, since it allows an assessment of the energy transfer relationship between the carotenoids and chlorophylls within the antenna complex. 

Dietary fats are required for carotenoid uptake by intestinal cells. Fats have an important role in the continuation of the process of carotenoid absorption, because the human intestine is incapable of secreting significant quantities of chylomicrons into the bloodstream in the absence of fats (Ornelas-Paz and others 2008b). Some studies have suggested that at least 5 g/day of dietary fat are required for suitable (3-carotene absorption (West and Castenmiller 1998), whereas others suggested the consumption... 

Sun M and Temelli F. 2006. Supercritical carbon dioxide extraction of carotenoids from carrot using canola oil as a continuous co-solvent. J Supercrit Fluids 37(3) 397-408. 

Although the benefits of many functional ingredients have yet to be proven, there is a possibility for new health problems to arise if the market for fortified functional foods continues to expand. Some consumers may ingest excessive amounts of certain nutritional food additives such as iron, which could lead to an increased incidence of hemachromatosis in genetically predisposed people. Fortification with specific carotenoids may competitively inhibit the bioavailability of other carotenoids, perhaps leading to adverse physiological consequences. 

Regulation. Inhibition continues to be useful for the elucidation of some details of carotenoid biosynthesis some examples have been reported above. 4-[ -... 

The body s natural defenses against overenthusiastic oxidation include a-lipoic acid, reduced glutathione, ascorbic acid, the tocopherols, the carotenoids, and a number of enzymes such as epoxide hydrolase and the like. Very efficient DNA repair systems also operate defensively. These various means are remarkably effective, but DNA assault is continuous, cumulative, and implacable. Thus, many degenerative diseases are associated with aging because of the gradual slippage in functional fidelity of cellular machinery which occurs with age. 

Paprika can be extracted to recover carotenoids, not only with CO2 but also with other gases. For example, by using ethane or ethylene, better results were obtained for the yield, extraction time, and quality of product. The solubilities of carotenoids are better in these gases, which is why the consumption of solvent and the extraction time were reduced. Practically water-free dye-concentrate was recovered by supercritical fluid ethane (under the conditions extraction 250 bar, 45°C separation 46 bar, 45 °C). The separation of pungent substances (capsaicinoids, free fatty acids) from the pigments can be carried out effectively in a continuous, counter-current extraction column with a large number of theoretical plates. 

Basic Protocol 2 Fast Atom Bombardment, Liquid Secondary Ion Mass Spectrometry, and Continuous-Flow Fast Atom Bombardment of Carotenoids F2.4.2... 

This protocol begins with the extraction of a dehydrated sample. It continues with a saponification scheme to initiate the isolation of the carotenoid mixture. During saponification, the esters are hydrolyzed and the free pigments released. Then, to continue the isolation, column chromatography is suggested as a simple and fast means of separating the three main groups of carotenoids based on their different polarities. 

Mass Spectrometry of Carotenoids NOTE For LC/MS or flow injection using continuous-flow FAB, the mass spectrometer must be equipped with a continuous-flow ionization source. 

FAB ionization has been used in combination with LC/MS in a technique called continuous-flow FAB LC/MS (Schmitz et al., 1992 van Breemen et al., 1993). Although any standard HPLC solvent can be used, including methyl-ferf-butyl ether and methanol, the mobile phase should not contain nonvolatile additives such as phosphate or Tris buffers. Volatile buffers such as ammonium acetate are compatible at low concentrations (i.e., <10 mM). Continuous-flow FAB has also been used in combination with MS/MS (van Breemen et al., 1993). The main limitationsof continuous-flow FAB compared to other LC/MS techniques for carotenoids, such as ESI and APCI, are the low flow rates and the high maintenance requirements. During use, the 3-nitrobenzyl alcohol matrix polymerizes on the continuous-flow probe tip causing loss of sample signal. As a result, the continuous-flow probe must be removed and cleaned approximately every 3 hr. 

---