Low carotenoid concentration

HOW THE MEMBRANE ITSELF AFFECTS DISTRIBUTION AND LOCALIZATION OF CAROTENOIDS IN THE LIPID BlLAYER (LOW CAROTENOID CONCENTRATION)... 

It has been shown in many studies that protective effects of carotenoids can be observed only at small carotenoid concentrations, whereas at high concentrations carotenoids exert pro-oxidant effects via propagation of free radical damage (Chucair et al., 2007 Lowe et al., 1999 Palozza, 1998, 2001 Young and Lowe, 2001). For example, supplementation of rat retinal photoreceptors with small concentrations of lutein and zeaxanthin reduces apoptosis in photoreceptors, preserves mitochondrial potential, and prevents cytochrome c release from mitochondria subjected to oxidative stress induced by paraquat or hydrogen peroxide (Chucair et al., 2007). However, this protective effect has been observed only at low concentrations of xanthophylls, of 0.14 and 0.17 pM for lutein and zeaxanthin, respectively. Higher concentrations of carotenoids have led to deleterious effects (Chucair et al., 2007). 

Also degradation products of carotenoids exhibit immunomodulatory effects. For example, P-carotene degradation products can stimulate production of superoxide by activated neutrophils at low micromolar concentrations but exhibit inhibitory effects at concentrations above 20 pM (Siems et al., 2003). 

Chlorella zofingensis cells are transferred to a growth medium, with a low nitrogen concentration (10% of normal concentration). After approximately 6-8 wk they develop a red colour, due to the decomposition of chlorophylls and synthesis of secondary carotenoids (stored in lipid droplets within the cytoplasm of the cells). At this stage the chloroplast are intact, although the surface area of thylacoids is mostly reduced. 

Resonance Raman Spectroscopy. A review of the interpretation of resonance Raman spectra of biological molecules includes a consideration of carotenoids and retinal derivatives. Another review of resonance Raman studies of visual pigments deals extensively with retinals. Excitation profiles of the coherent anti-Stokes resonance Raman spectrum of j8-carotene have been presented. Resonance Raman spectroscopic methods have been used for the detection of very low concentrations of carotenoids in blood plasma and for the determination of carotenoid concentrations in marine phytoplankton, either in situ or in acetone extracts. ... 

The concentrations of carotenoids and the level of oxygen they are exposed to can also influence their antioxidant activities. At low oxygen partial pressures, diverse carotenoids effectively inhibit in vitro oxidation reactions, and their antioxidative abilities increase with increasing carotenoid concentration." " As oxygen levels are increased, however, their antioxidant potential typically decreases." " Certain carotenoids, notably P-carotene but also lycopene, exhibit unusual behavior beyond a threshold carotenoid concentration, they actually decrease in antioxidant ability with increasing carotenoid concentration, and this effect is further exacerbated at high oxygen levels." This prooxidant... 

The carotenoid activity during oxidation is strongly influenced by the oxygen pressure (PO2) of the experimental conditions. Kiokias and Oreopoulou have shown that certain natural carotenoid mixtures (paprika, bixin and tomato, and palm-oil preparations) inhibited the azo-initiated oxidation of sunflower oil-in-water emulsions (operated rapidly under low pOj) in terms of both primary and secondary oxidation products. However, other studies " concluded that carotenoids not only did not inhibit aerial lipid autoxidation (high PO2) but even exerted a prooxidant character, a phenomenon also observed at high carotenoid concentrations that could be due mainly to a more increased formation of carotene-peroxyl radicals, promoting the propagation of autoxidation. 

This method offers the evaluation of spectra showing strong background noise and only low spectral variation and the prediction of the relative carotenoid concentration by using only a single reference spectrum. In addition, this reference compound does not need to be structurally identical to the target compound, as demonstrated for the predicted versus measured target spectrum for carotenoids [162]. 

Russell 1992), and volunteers who habitually have a low plasma carotenoid concentration show a much smaller (but proportional) response than volunteers who have a high fasting plasma carotenoid concentration. However there is a high degree of intra-individual consistency (Borel et al. 1998). These results have been interpreted as reflecting differences in absorption. 

The tomato waste/solvent ratio was 1 10 and different extraction parameters (type of solvent, extraction time, temperature, and number of successive extractions) were tested. Regarding the extraction temperature, the experiments were carried out at 25 C. Carotenoid concentration (expressed as lycopene, since this carotenoid represents around 80-90% of total tomato carotenoids) increased with time and the equilibrium concentration was achieved at approximately 30 min of extraction time. The concentration was considerably low in ethanol (0.38 mg/L) and higher in ethyl lactate (12.52 mg/L) at equilibrium. The concentration for the other solvents was between 1.99-2.82 mg/L. 

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