The effect of different light regimes on pigments in Coscinodiscus granii.

The influence of six different light regimes throughout the photosynthetically active radiation range (from 400 to 700 nm, including blue, green, yellow, red-orange, red, and white) at two intensities (100 and 300 µmol photons m-2 s-1) on pigmentation was assessed for the centric marine diatom Coscinodiscus granii for the first time. Chlorophyll (Chl) a and fucoxanthin were the dominating pigments in all treatments. The cellular concentrations of light harvesting pigment (Chl a, Chl c1 + c2, and fucoxanthin) were higher at 100 than at 300 µmol photons m-2 s-1 at all wavelengths, with the largest increases at red and blue light. The normalized concentrations of photoprotective pigments (violaxanthin, zeaxanthin, diadinoxanthin, and diatoxanthin) were higher at high light intensity than in cells grown at low light intensity. An increase in ß-carotene in low light conditions is expected as the increased Chl a was related to increased photosynthetic subunits which require ß-carotene (bound to photosystem core). At 300 µmol photons m-2 s-1, yellow light resulted in significantly lower concentration of most of the detected pigments than the other wavelengths. At 100 µmol photons m-2 s-1, W and B light led to statistically lower and higher concentration of most of the detected pigments than the other wavelengths, respectively.

Ultrasonic pretreatment of carrot slices: Effects of sonication source on drying kinetics and product quality.

In this study effects of ultrasonic pretreatment with different sonication sources on drying behavior of carrot slices were evaluated. Fresh carrot slices were pretreated with ultrasonic probe at 65, 75 and 85 W or ultrasonic bath at 10, 20 and 30°C for 3, 5 and 10 min before air drying. Water gain % and solid loss % of pretreated samples were calculated and color values, ß-carotene content and rehydration ratios of dried samples were determined. Drying behavior of the pretreated samples was evaluated and the drying data were fitted to thin layer drying models. Constant drying rate period was not observed for the carrot slices; however two definite falling-rate periods having different slopes were obtained. Drying time was significantly reduced (up to 20%) depending on the type of pretreatment. The redness value, total color difference and Chroma values of pretreated and control samples were in the same group (p>0.05). ß-carotene content of ultrasonic bath pretreated samples were significantly higher than the samples pretreated with ultrasonic probe and the sample dried without any pretreatment as well (p<0.05). Also rehydration ratios of control samples were found lower than the ultrasound pretreated samples.

Lipid and carotenoid cooperation-driven adaptation to light and temperature stress in Synechocystis sp. PCC6803.

Polyunsaturated lipids are important components of photosynthetic membranes. Xanthophylls are the main photoprotective agents, can assist in protection against light stress, and are crucial in the recovery from photoinhibition. We generated the xanthophyll- and polyunsaturated lipid-deficient ROAD mutant of Synechocystis sp. PCC6803 (Synechocystis) in order to study the little-known cooperative effects of lipids and carotenoids (Cars). Electron microscopic investigations confirmed that in the absence of xanthophylls the S-layer of the cellular envelope is missing. In wild-type (WT) cells, as well as the xanthophyll-less (RO), polyunsaturated lipid-less (AD), and the newly constructed ROAD mutants the lipid and Car compositions were determined by MS and HPLC, respectively. We found that, relative to the WT, the lipid composition of the mutants was remodeled and the Car content changed accordingly. In the mutants the ratio of non-bilayer-forming (NBL) to bilayer-forming (BL) lipids was found considerably lower. Xanthophyll to ß-carotene ratio increased in the AD mutant. In vitro and in vivo methods demonstrated that saturated, monounsaturated lipids and xanthophylls may stabilize the trimerization of Photosystem I (PSI). Fluorescence induction and oxygen-evolving activity measurements revealed increased light sensitivity of RO cells compared to those of the WT. ROAD showed a robust increase in light susceptibility and reduced recovery capability, especially at moderate low (ML) and moderate high (MH) temperatures, indicating a cooperative effect of xanthophylls and polyunsaturated lipids. We suggest that both lipid unsaturation and xanthophylls are required for providing the proper structure and functioning of the membrane environment that protects against light and temperature stress.

Radical production by infrared A irradiation in human tissue.

The influence of the ultraviolet (UV) irradiation of the sun on the formation of free radicals in human skin is well investigated. Up to now, only small amounts of data are available stating that infrared (IR) irradiation can produce free radicals in the skin. In the present study, the formation of free radicals in human skin, subsequent to IRA irradiation (600-1,500 nm), has been demonstrated by means of two different methods. Firstly, the radical formation was detected indirectly by the degradation of the cutaneous carotenoid antioxidants beta-carotene and lycopene, which was investigated in vivo by resonance Raman spectroscopic measurements. Secondly, the direct observation of produced radicals subsequent to IRA irradiation of the skin was performed in vitro by electron paramagnetic resonance spectroscopy. Taking into account the results of the present study and previous UV light studies, it can be expected that also solar irradiation in the visible spectral range will produce free radicals in the human skin. Therefore, the current sun protection strategies should be reconsidered. Furthermore, it was shown in the present study that the side effect in the form of radical formation could be significantly reduced by increasing the protection system of the human organism in form of the antioxidant network.

Improvement of thermal and UV-light stability of ß-carotene-loaded nanoemulsions by water-soluble chitosan coating.

ß-Carotene is a vitamin A precursor and antioxidant with well-known health benefits; however, it is unstable and poorly soluble in water. In this study, ß-carotene-loaded nanoemulsions (BC-NEs) and water-soluble chitosan-coated BC-NEs (WSC-BC-NEs) were prepared to improve the stability of ß-carotene against high temperature and UV-light. WSC-BC-NEs were round droplets with two distinct layers and an average diameter of 218 nm and zeta potential of +40 mV. The thermal and UV light stability of the WSC-BC-NEs were improved compared to those of both free ß-carotene and BC-NEs. Free ß-carotene degraded readily during storage, particularly when exposed to high temperature and UV light. By contrast, the WSC-BC-NEs retained 82.0% of ß-carotene after 21 days of storage at 37 °C, and 77.6% after 21 days of UV light exposure (253 nm) at room temperature. Furthermore, compared with the BC-NEs, the WSC-BC-NEs improved the thermal stability of ß-carotene by about 45.1% after 21 days at 37 °C, and by 28.6% after 21 days of UV light exposure (253 nm). Therefore, the WSC-BC-NEs effectively increased the stability of the encapsulated ß-carotene, and show potential for application in the food and beverage industries.

Cyclic endoperoxides of beta-carotene, potential pro-oxidants, as products of chemical quenching of singlet oxygen.

Photoprotection by carotenoids is generally considered to be based on the photophysical quenching of triplets and singlet oxygen. There is also accumulating evidence of an alternative, chemical quenching of triplets and singlet oxygen by carotenoids. We report the identification of relatively stable cyclic mono- and diendoperoxides as first products of such an alternative reaction. Nevertheless, these species remain reactive and in the dark cause autooxidation of beta-carotene in our model system. Their formation could explain the intriguing pro-oxidant and cytotoxic activity of carotenoids.

Heat-induced and light-induced isomerization of the xanthophyll pigment zeaxanthin.

Zeaxanthin is a xanthophyll pigment that plays important physiological functions both in the plant and in the animal kingdom. All-trans is a stereochemical conformation of zeaxanthin reported as specific for the thylakoid membranes of the photosynthetic apparatus and the retina of an eye. On the other hand, the pigment is subjected, in natural environment, to the conditions that promote stereochemical isomerization, such as illumination and elevated temperature. In the present work, the light-induced and heat-induced (the temperature range 35-95 degrees C) isomerization of all-trans zeaxanthin in organic solvent environment has been analyzed by means of the HPLC technique. The 13-cis conformation has been identified as a major one among the isomerization products. The activation energy of the all-trans to 13-cis isomerization has been determined as 83 +/- 4 kJ/mol and the activation energy of the back reaction as 30 +/- 7 kJ/mol. The reaction of isomerization of the all-trans zeaxanthin at 25 degrees C was substantially more efficient upon illumination. Four different wavelengths of light have been selected for photo-isomerization experiments: 450, 540, 580 and 670 nm, corresponding to the electronic transitions of zeaxanthin from the ground state to the singlet excited states: 1(1)Bu+,3(1)Ag-,1(1)Bu- and 2(1)Ag-, respectively. The quantum efficiency of the all-trans zeaxanthin isomerization induced by light at different wavelengths: 450, 540, 580 and 670 nm was found to differ considerably and was in the ratio as 1:15:160:29. The sequence of the quantum efficiency values suggests that the carotenoid triplet state 1(3)Bu, populated via the internal conversion from the 1(3)Ag triplet state which is generated by the intersystem crossing from the 1(1)Bu- state may be involved in the light-induced isomerization. A physiological importance of the isomerization of zeaxanthin in the retina of an eye, photosynthetic apparatus and of the pigment active as a blue light photoreceptor in stomata is briefly discussed.

Photostability evaluation of five UV-filters, trans-resveratrol and beta-carotene in sunscreens.

Trans-resveratrol (RES) is used in cosmetic formulations and beta-carotene (BTC) is a classical sunscreen antioxidant, but their photostability in sunscreens, a property directly correlated to performance and safety has not been addressed in the literature. This paper reports the assessment of RES and/or BTC influence on the photostability of five UV-filters (octyl methoxycinnamate - OMC, avobenzone -AVO, octocrylene - OCT, bemotrizinole - BMZ, octyltriazone - OTZ) in three different combinations after UVA exposure followed by the identification of degradation products and the assessment of photoreactivity. The evaluation of sunscreen photostability was performed by HPLC and spectrophotometric analysis, and degradation products were identified by GC-MS analysis. Components RES, BTC, OMC and AVO were significantly degraded after UV exposure (reduction of around 16% in recovery). According to HPLC analysis, all formulations presented similar photostability profiles. Eleven degradation products were identified in GC-MS analysis, among them products of RES, BTC, OMC and AVO photodegradation. All evaluated formulations were considered photoreactive, as well as the isolated compounds RES and AVO. Considering HPLC, spectrophotometric and GC-MS results, it is suggested that formulations containing BMZ were considered the most photostable. The combination RES+BTC in a sunscreen improved the photostability of AVO. The benefits of using a combination of antioxidants in sunscreens was demonstrated by showing that using RES+BTC+studied UV-filters led to more photostable formulations, which in turn implies in better safety and efficacy.

Beta-carotene suppresses UVA-induced HO-1 gene expression in cultured FEK4.

The ultraviolet region of sunlight causes a significant oxidative stress to human skin cells and modulates expression of a series of genes in dermal fibroblasts and other cell types. The human heme oxygenase 1 (HO-1) gene is strongly activated within the first hours that follow UVA irradiation of normal human dermal fibroblasts (FEK4) and this response is being used as a marker of oxidative stress in cells. It has been shown that the induction of this gene occurs via singlet oxygen ((1)O(2)) produced upon interaction of UVA radiation with an as yet undefined cellular chromophore. Carotenoids, as the most potent singlet oxygen quenchers in nature, are expected to effectively suppress the UVA-induced HO-1 gene activation in human cells. In this study, we measured the suppression of UVA-induced levels of HO-1 mRNA after the addition of a series of six all-trans-beta-carotene concentrations (0.07, 0.2, 0.8, 2.3, 8.0, and 21 microM) to the culture medium of exponentially growing FEK4 cells. The corresponding levels of beta-carotene uptake and apo-carotenal formation were measured following HPLC separation. The results of this study show a concentration-dependent suppression of UVA- (250 kJ/m(2)) induced transcriptional activation of HO-1 in exponentially growing FEK4 cells by beta-carotene. Suppression occurred at concentrations that have been observed in human plasma after dietary supplementation with beta-carotene.

Pulse radiolysis studies of beta-carotene in oxygenated DMSO solution. Formation of beta-carotene radical cation.

The spectroscopic and kinetic characteristics of beta-carotene radical cation (beta-carotene(.+)) were studied by pulse radiolysis in aerated DMSO solution. The buildup of beta-carotene(.+) with k(1) = (4.8 +/- 0.2) x 10(8) dm(3) mol(-1) s(-1) [lambda(max) = 942 nm, epsilon = (1.6 +/- 0.1) x 10(4) dm(3) mol(-1) cm(-1)] results from an electron transfer from beta-carotene to DMSO(.+). The beta-carotene(.+) species decays exclusively by first-order reaction, k = (2.1 +/- 0.1) x 10(3) s(-1), probably by two processes: (1) at low substrate concentration by hydrolysis and (2) at high concentrations also by formation of dimer radical cation (beta-carotene)(2)(.+). Under the experimental conditions, a small additional beta-carotene triplet-state absorption ((3)beta-carotene) in the range of 525 to 660 nm was observed. This triplet absorption is quenched by oxygen (k = 7 x 10(4) s(-1)), resulting in singlet oxygen ((1)O(2)), whose reactions can also lead to additional formation of beta-carotene(.+).

Photodynamics of the bacteriochlorophyll-carotenoid system. 1. Bacteriochlorophyll-photosensitized oxygenation of beta-carotene in acetone.

Carotenoids are well-known physical quenchers of chlorophyll excited states and reactive oxygen species both in vivo and in vitro. They may also be involved in chemical quenching undergoing, e.g. isomerizations or oxidations. We have found that beta-carotene (Car) in aerobic acetone is rapidly oxygenated under strong illumination with red light (lambda exc > or = 630 nm) in the presence of bacteriopheophytin a. At the same time the photosensitizer undergoes only slight (< 10%) photodegradation. By preparative high-performance liquid chromatography as many as seven major products of oxygen attachment to Car have been isolated. Their molecular masses show that Car sequentially accumulates up to six oxygen atoms while its C40-skeleton remains intact.

Photodynamics of the bacteriochlorophyll-carotenoid system. 2. Influence of central metal, solvent and beta-carotene on photobleaching of bacteriochlorophyll derivatives.

Bacteriochlorophyll (BChl) derivatives (with central Mg replaced by metal "M") ([M]-BChl with M = 2H, Mg, Zn, Pd, Cu) have been investigated for their photodynamic capacity and stability toward photodegradation in organic solvents and aqueous micellar solution. A protocol has been developed for screening new sensitizers. BChl and [Zn]-BChl are efficient sensitizers, but they are also quickly degraded by the reactive oxygen species (ROS) produced by autosensitization, as well as by hetero-sensitization with 17(4)-methyl-13(2)-demethoxycarbonyl-pheophorbide a (MPP). Photostable [Cu]-BChl is a poor sensitizer, whereas [Pd]-BChl and bacteriopheophytin a are not only very efficient sensitizers but are also very stable toward ROS. beta-Carotene is no efficient physical quencher of ROS in the system; rather, it acts as a photochemical quencher that competes with [M]-BChl and undergoes photooxygenation at high rates. Photolability seems to depend on the pigment oxidation potential and, in parallel, on the presence of central metals preferring coordination numbers higher than 4, whereas photodynamic capacity depends on long excited state life-times of the pigment or efficient intersystem crossing (or both).

The light environment and cellular optics of the snow alga Chlamydomonas nivalis (Bauer) Wille.

The alga Chlamydomonas nivalis lives in a high-light, cold environment: persistent alpine snowfields. Since the algae in snow receive light from all angles, the photon fluence rate is the critical parameter for photosynthesis, but it is rarely measured. We measured photon irradiance and photon fluence rate in the snow that contained blooms of C. nivalis. On a cloudless day the photon fluence rate at the snow surface was nearly twice the photon irradiance, and it can be many times greater than the photon irradiance when the solar angle is low or the light is diffuse. Beneath the surface the photon fluence rate can be five times the photon irradiance. Photon irradiance and photon fluence rate declined exponentially with depth, approximating the Bouguer-Lambert relationship. We used an integrating sphere to measure the spectral characteristics of a monolayer of cells and microscopic techniques to examine the spectral characteristics of individual cells. Astaxanthin blocked blue light and unknown absorbers blocked UV radiation; the penetration of these wavelengths through whole cells was negligible. We extracted astaxanthin, measured absorbance on a per-cell basis and estimated that the layer of astaxanthin within cells would allow only a small percentage of the blue light to reach the chloroplast, potentially protecting the chloroplast from excessive light.

Synergistic effect of dehydroascorbic acid and mixtures with vitamin E and beta-carotene on mitomycin C efficiency under irradiation in vitro.

Experiments in vitro have shown that dehydroascorbic acid (DHA) possesses antitumor properties under irradiation, which are gradually enhanced by combination with beta-carotene or vitamin E. On the other hand the cytostatic efficiency of mitomycin C (MMC) is increased from deltaD37 = -93 up to deltaD37 = -141 in the presence of DHA. It has also been shown that Escherichia coli bacteria are able, to some extent, to reduce DHA to ascorbate under the same experimental conditions. The results are of interest for the radiation therapy of cancer.

Molecular flexibility of retinoic acid under white fluorescent light.

Among the series of metabolic analogs of the eccentric cleavage pathway of beta-carotene with different side chain lengths, retinoic acid was shown to have exceedingly higher molecular flexibility to undergo photoisomerization into the geometrical isomers under white fluorescent light. When irradiated with white fluorescent lamps (1,200 lx), the velocity of photoisomerization of all-trans-retinoic acid (8.4 x 10(-7) mol/L.min) was exceedingly higher than those of the other analogs: ionylideneacetic acid (4 x 10(-8) mol/L.min), ionylidenecrotonic acid (3.0 x 10(-7) mol/L.min), all-trans-beta-apo-14'-carotenoic acid (1.7 x 10(-7) mol/L.min), all-trans-beta-apo-12'-carotenoic acid (1.3 x 10(-7) mol/L.min), and all-trans-beta-apo-8'-carotenoic acid (0.1 x 10(-7) mol/L.min). beta-Carotene did not undergo photoisomerization under the experimental conditions. The molecular flexibility of retinoic acid is assumed to be an important basis of the mechanism of action of retinoic acid.

Reduction of deoxynivalenol contaminating corn silage by short-term ultraviolet irradiation: a pilot study.

We evaluated the effects of short-term (up to 60 min) irradiation of corn silage with ultraviolet (UV) light (intensity: 1.5 mW/cm(2) at 254 nm UV-C wavelength), along with constant stirring of the silage, on the concentration of deoxynivalenol (DON), a major feed-contaminating mycotoxin, and those of α-tocopherol (vitamin E) and ß-carotene (pro-vitamin A). The initial DON concentration in artificially contaminated silage was set at approximately 60 µg/g dry silage weight. After irradiation, the level of DON was decreased significantly (P<0.05) by approximately 13 µg/g (22%) on average at 30 min, and by 12 µg/g (21%) at 60 min. However, the concentrations of the vitamins remained relatively unaffected. Although further improvement is needed, short-term UV irradiation seems a promising on-farm method for reducing the level of DON in feedstuffs.

Resonance Raman spectroscopy as an effective tool for the determination of antioxidative stability of cosmetic formulations.

Carotenoids beta-carotene, lutein, lycopene and others are well-known powerful antioxidants acting as an effective neutralizer of free radicals produced in the human organism as a result of the influence of stress factors, such as UV irradiation. The protective effect of antioxidants is used in cosmetic products to increase the skin protection against the destructive action of free radicals and for the stabilization of formulations against oxidation. In the skin, the different antioxidant substances form protection chains to avoid their destruction by the interaction with the free radicals. Similar effects have to be expected also in topically applied formulations. In the present study the influence of different mixtures of antioxidants (beta-carotene, vitamins C and E) on the stability of antioxidants in formulations used for skin treatment was investigated. The measurements were carried out by using non-invasive resonance Raman spectroscopy for the detection of the carotenoid concentration in the cosmetic formulations.

UV-A mediated induction of carotenoid accumulation in Dunaliella bardawil with retention of cell viability.

The effect of adding UV-A radiation (320-400 nm) to photosynthetically active radiation (PAR, 400-700 nm) during growth of the photosynthetic marine microalga Dunaliella bardawil was investigated in this work in terms of cell growth and carotenoid production. Although signs of slow cell growth (slight reduction of chlorophyll and protein content) were observed after 24 h of cell exposure to UV-A (40 micromol photons m(-2) s(-1) and 70 micromol photons m(-2) s(-1)) plus 140 micromol photons m(-2) s(-1) PAR , 84 h exposure to these UV-A conditions slightly stimulated cell growth and increased the photosynthetic efficiency of the exposed cultures. The enhanced cell growth was coupled with an increase in total carotenoid content. Besides beta-carotene as the major pigment, increases in the well-known antioxidants lutein and zeaxanthin of about 3-fold and 5-fold, respectively, were determined in cultures exposed to UV-A radiation of 70 micromol photons m(-2) s(-1)for 84 h. As a consequence, far from being negative to cell growth, low and medium UV-A radiation are stress factors that could be successfully applied to long-term processes for large scale carotenoid production using D. bardawil cultures with retention of cell viability. UV-A exposure has the advantage of being a factor either easily applied or removed as required, in contrast to other nutrient stresses, which require medium replacement for their application.

Reduction in photostability by the esterification of beta-cryptoxanthin.

Liposomes, in which beta-carotene, beta-cryptoxanthin, zeaxanthin, beta-cryptoxanthin palmitate or beta-cryptoxanthin acetate had been embedded, were irradiated by UVA, and the rate of degradation of each carotenoid was measured. There was no significant difference in the degradation rate between beta-carotene, beta-cryptoxanthin and zeaxanthin. The degradation rates of beta-cryptoxanthin palmitate and beta-cryptoxanthin acetate were faster than that of beta-cryptoxanthin, and the degradation rate of beta-cryptoxanthin palmitate was faster than that of beta-cryptoxanthin acetate.