Spectroscopic study on formation of aggregated structures by carotenoids: Role of water

Fabrication, characterization, stability and re-dispersity of H-aggregates fucoxanthin/whey protein/chitosan nanoparticles

This study aimed to establish a unique and controlled protocol of H-aggregates fucoxanthin and improve the water dispersibility and stability of H-aggregates fucoxanthin. H-aggregates fucoxanthin has been controllably prepared by regulating the key factor of the molecular self-aggregation of fucoxanthin in hydrated-organic systems. The H-aggregates fucoxanthin/BSA/chitosan nanoparticles (H-FBC-NPs), with a hydrated size around 171 ± 4 nm, were prepared by adjusting the three types of whey protein and initial concentration of fucoxanthin, which was constructed by a layer-by-layer self-assembly method. The spectroscopy studies indicated that chitosan and BSA formed hydrophobic microdomain by the intermolecular electrostatic interactions with remarkable changes of secondary structure in protein, which encapsulate fucoxanthin as H-aggregate. H-FBC-NPs were nearly spherical and uniformly dispersed via SEM and TEM. The EE of fucoxanthin in the H-FBC-NPs was >93.6 %. The successfully prepared H-FBC-NPs nanosuspension was lyophilized by vacuum freeze-drying technique with lyoprotectants, which was applied to the long-term preservation of H-FBC-NPs. H-FBC-NPs were stable within 48 h at 4 °C, 25 °C, 37 °C and different pH-value environments. This study broadens the application of fucoxanthin and its H-aggregates in the fields of food and biomedicine.

Discovery of ultra-weakly coupled β-carotene J-aggregates by machine learning

Carotenoid aggregates are omnipresent in natural world and can be synthesized in hydrophilic environments. Despite different types of carotenoid aggregates have been reported hitherto, the way to predict the formation of carotenoid aggregates, i.e. H- or J-aggregates, is still challenging. Here, for the first time, we established machine learning models that can predict the formation behavior of carotenoid aggregates. The models are trained based on a database containing different types of carotenoid aggregates reported in the literatures. With the help of these machine learning models, we found a series of unknown types of β-carotene J-aggregates. These novel aggregates are ultra-weakly coupled and have absorption bands up to 700 nm, different from all the carotenoid aggregates reported previously. Our work demonstrates that the machine learning is a powerful tool to predict the formation behavior of carotenoid aggregates and can further lead into the discovery of new carotenoid aggregates for different applications.

Astaxanthin Isomers: A Comprehensive Review of Isomerization Methods and Analytic Techniques

The presence of multiple conjugated double bonds and chiral carbon atoms endows astaxanthin with geometric and optical isomers, and these isomers widely exist in biological sources, food processing, and in vivo absorption. However, there remains no systematic summary of astaxanthin isomers regarding isomerization methods and analytic techniques. To address this need, this Review focuses on a comprehensive analysis of Z-isomerization methods of astaxanthin, including solvent system, catalyst, and heat treatment. Comparatively, high-efficiency and health-friendly methods are more conducive to put into practical use, such as food-grade solvents and food-component catalysts. In addition, we outline the recent advances in analysis techniques of astaxanthin isomers, as well as the structural characteristics reflected by various methods (e.g., HPLC, NMR, FTIR, and RS). Furthermore, we summarized the related research on the safety evaluation of astaxanthin isomers. Finally, future trends and barriers in Z-transformation and analysis of astaxanthin isomers are also discussed.

Mechanism underlying joint loading and controlled release of β-carotene and curcumin by octenylsuccinated Gastrodia elata starch aggregates

This study aimed to fabricate a novel codelivery system to simultaneously load β-carotene and curcumin in a controlled and synergistic manner. We hypothesized that the aggregates of octenylsuccinated Gastrodia elata starch (OSGES) could efficiently load and control the release of β-carotene and curcumin in combination. Mechanisms underlying the self-assembly of OSGES, coloading, and corelease of β-carotene and curcumin by relevant aggregates were studied. The OSGES could form aggregates with a size of 120.2 nm containing hydrophobic domains surrounded by hydrophilic domains. For coloading, the increased solubilities were attributed to favorable interactions between β-carotene and curcumin as well as interactions with octenyl and starch moieties via hydrophobic and hydrogen-bond interactions, respectively. The β-carotene and curcumin molecules occupied the interior and periphery of hydrophobic domains of OSGES aggregates, respectively, and they did not exist in isolation but interacted with each other. The β-carotene and curcumin combination-loaded OSGES aggregates with a size of 310.5 nm presented a more compact structure than β-carotene-only and curcumin-only loaded OSGES aggregates with sizes of 463.5 and 202.9 nm respectively, suggesting that a transition from a loose cluster to a compact cluster was accompanied by coloading. During in vitro digestion, the joint effect of β-carotene and curcumin prolonged their release and increased their bioaccessibility due to competition between favorable hydrophobic and hydrogen-bond interactions and the unfavorable structure erosion and relaxation of the loaded aggregates. Therefore, OSGES aggregates were designed for the codelivery of β-carotene and curcumin, indicating their potential to be applied in functional foods and dietary supplements.

Co-aggregation between whey proteins and carotenoids from yellow mombin (Spondias mombin): Impact of carotenoids' self-aggregation

The interaction between whey proteins and carotenoid is reported to improve carotenoid solubility and stability, however, the strong trend of carotenoids to aggregate when in polar systems is often neglected in papers addressing their molecular interaction. Therefore, this study focused on characterizing the aggregative behavior of the carotenoids from yellow mombin (Spondias mombin) and to understand how these carotenoids behave when added to aqueous dispersions of whey proteins. Carotenoids-rich extract, containing mainly β-cryptoxanthin and lutein, was obtained from freeze-dried yellow mombin pulp and its aggregative behavior in ethanol/water medium was studied. By increasing the medium polarity, carotenoids trend to form J-aggregation, causing a drop in the color intensity of the solution. When added to whey protein aqueous dispersions, rather than a protein-carotenoid bimolecular interaction, the formation of co-aggregates between carotenoids and whey proteins was evidenced by preparative size exclusion chromatography. These results may contribute to the developing functional food products.

Lycopene, but not zeaxanthin, serves as a skeleton for the formation of an orthorhombic organization of intercellular lipids within the lamellae in the stratum corneum: Molecular dynamics simulations of the hydrated ceramide NS bilayer model

Carotenoids play an important role in the protection of biomembranes against oxidative damage. Their function depends on the surroundings and the organization of the lipid membrane they are embedded in. Carotenoids are located parallel or perpendicular to the surface of the lipid bilayer. The influence of carotenoids on the organization of the lipid bilayer in the stratum corneum has not been thoroughly considered. Here, the orientation of the exemplary cutaneous carotenoids lycopene and zeaxanthin in a hydrated ceramide NS24 bilayer model and the influence of carotenoids on the lateral organization of the lipid bilayer model were studied by means of molecular dynamics simulations for 32 °C and 37 °C. The results confirm that lycopene is located parallel and zeaxanthin perpendicular to the surface of the lipid bilayer. The lycopene-loaded lipid bilayer appeared to have a strong orthorhombic organization, while zeaxanthin-loaded and pure lipid bilayers were organized in a disordered hexagonal-like and liquid-like state, respectively. The effect is stronger at 32 °C compared to 37 °C based on p-values. Therefore, it was assumed that carotenoids without hydroxyl polar groups in their structure facilitate the formation of the orthorhombic organization of lipids, which provides the skin barrier function. It was shown that the distance between carotenoid atoms matched the distance between atoms in the lipids, indicating that parallel located carotenoids without hydroxyl groups serve as a skeleton for lipid membranes inside the lamellae. The obtained results provide reasonable prediction of the overall qualitative properties of lipid model systems and show the importance of parallel-oriented carotenoids in the development and maintenance of the skin barrier function.

Effect of environmental factors on the aggregation behavior of astaxanthin in water

Molecular aggregation is a common phenomenon widely found in natural organisms, which is crucial for some specific functions of biological systems. To study the aggregating behavior of hydrophobic carotenoids in water, astaxanthin was employed and dispersed under different surroundings to induce aggregation. The results showed that astaxanthin tended to form J- or H-type aggregates when the water content was higher than 60%. Both hydrochloric acid (HCl) and sodium hydroxide (NaOH) were beneficial for the formation of astaxanthin J-aggregates, but they were not good for inducing H-aggregates. Small-molecule electrolytes, like sodium salts, mostly played an enormous hindrance role to the formation of astaxanthin H- and J-aggregates, except for sodium chloride (NaCl) which helped astaxanthin to form J-aggregates. Both sodium periodate (NaIO₄) and sodium acetate (CH₃COONa) could prevent the formation of astaxanthin H- and J-aggregates, but sodium chloride (NaCl) could only hinder the formation of H-aggregates. As for polyelectrolytes chitosan and DNA, the difference of chain structure led to different aggregation effects. The soft single chain of chitosan tended to induce J-aggregates formation, while double-stranded DNA preferred to guide the formation of H-aggregates. By choosing and integrating the advantageous environmental factors that facilitate each type of astaxanthin aggregates, J- and H-type astaxanthin aggregates were stably loaded in DNA/CS nanoparticles with distinct particle sizes. Controlled preparation of either H- or J-type aggregates is of great significance for further studies concerning the structure-activity relationship of carotenoid aggregates.

Simulation of absorption and scattering spectra of crystalline organic nanoparticles with the discrete dipole approximation: Effects of crystal shape, crystal size, and refractive index of the medium

The effect of the shape (habit) of crystalline organic nanoparticles on their absorption spectra is studied by simulations using the discrete dipole approximation, focusing, in particular, on the vibronic structure of the absorption bands in the spectra. Simulations predict a significant effect that, for sufficiently small particles, can be simply rationalized by the depolarization factor. The crystal size and the refractive index of the medium in which the nanoparticles are embedded are also found to have an effect on the absorption spectra. All factors mentioned are found to influence also the spectra of scattered light. These effects, already broadly documented for metallic nanoparticles, are here demonstrated theoretically for the first time for crystalline organic nanoparticles, providing novel insight into the optical response of such particles. The effects are expected to be displayed by all organic nanoparticles, as long as they have a well-defined crystal structure and are large enough for the optical properties to be understandable using a macroscopic dielectric tensor. The effects demonstrated here should be taken into account when rationalizing differences in absorption spectra of a substance in solution and in nanoparticle form, e.g., in deducing the type of intermolecular packing. The effects are much less pronounced for optically isotropic nanoparticles.

DFT study of Raman spectra of polyenes and ß-carotene: Dependence on length of polyene chain and isomer type

We carried out calculations of non-resonance Raman spectra of ß-carotene and polyenes CH₂(CHCH)_n-2CHCH₂ using the density functional theory (DFT). We revealed that the peak positions and intensities of the CC and CC stretching bands depend on length of the polyene chain and type of the isomer. Our experimental non-resonance Raman spectra of ß-carotene powder match well the DFT-simulated Raman spectrum of ß-carotene in the all-trans form. The peak positions and relative intensities of the CC and CC stretching bands of ß-carotene turned out to be similar in the resonance and non-resonance Raman spectra. An increase in the number of conjugated double bonds (n = 3-30) in a polyene structure results in a monotonous shift of the positions of the most intense CC and CC bands towards lower wavenumbers with an increase in the band intensities. An increase in the isomer number results in the monotonous decrease of the CC stretching band intensity for polyenes with 9, 10, 11, 15 and 24 double bonds. An increase in the isomer number inhomogeneously influences the form, position and intensity of the CC stretching band.

The non-homogenous distribution and aggregation of carotenoids in the stratum corneum correlates with the organization of intercellular lipids in vivo

The human stratum corneum (SC) contains an abundant amount of carotenoid antioxidants, quenching free radicals and thereby protecting the skin. For the precise measurements of the depth-dependent carotenoid concentration, confocal Raman microscopy is a suitable method. The quantitative concentration can be determined by the carotenoid-related peak intensity of a Gaussian function approached at ≈1524 cm^-1 using non-linear regression. Results show that the carotenoid concentration is higher at the superficial layers of the SC then decreases to a minimum at 20% SC depth and increases again towards the bottom of the SC. In the present work, two carotenoid penetration pathways into the SC are postulated. The first pathway is from the stratum granulosum to the bottom of the SC, while in the second pathway, the carotenoids are delivered to the skin surface by sweat and/or sebum secretion and penetrate from outside. The carotenoids are aggregated at the superficial layers, which are shown by high correlation between the aggregation states of carotenoids and the lateral organization of lipids. At the 30%-40% SC depths, the ordered and dense lipid molecules intensify the lipid-carotenoid interactions and weaken the carotenoid-carotenoid interaction and thus exhibit the disaggregation of carotenoids. At 90%-100% SC depths, the carotenoid-lipid interaction is weakened and the carotenoids have a tendency to be aggregated. Thus, the molecular structural correlation of carotenoid and SC lipid might be reserved in the intercellular space of the SC and also serves as the skeleton of the intercellular lipids.

Stabilization of Crystalline Carotenoids in Carrot Concentrate Powders: Effects of Drying Technology, Carrier Material, and Antioxidants

Coloring concentrates of carotenoid-rich plant materials are currently used in the food industry to meet the consumer's demand for natural substitutes for food colorants. The production of shelf-stable powders of such concentrates comes with particular challenges linked to the sensitivity of the active component towards oxidation and the complexity of the composition and microstructure of such concentrates. In this study, different strategies for the stabilization of crystalline carotenoids as part of a natural carrot concentrate matrix during drying and storage were investigated. The evaluated approaches included spray- and freeze drying, the addition of functional additives, and oxygen free storage. Functional additives comprised carrier material (maltodextrin, gum Arabic, and octenyl succinic anhydride (OSA)-modified starch) and antioxidants (mixed tocopherols, sodium ascorbate). Degradation and changes in the physical state of the carotenoid crystals were monitored during processing and storage. Carotenoid losses during processing were low (>5%) irrespective of the used technology and additives. During storage, samples stored in nitrogen showed the highest carotenoid retention (97-100%). The carotenoid retention in powders stored with air access varied between 12.3% ± 2.1% and 66.0% ± 5.4%, having been affected by the particle structure as well as the formulation components used. The comparative evaluation of the tested strategies allows a more targeted design of processing and formulation of functional carrot concentrate powders.

The Dose-Response Effect of Lycopene on Cerebral Vessel and Neuron Impairment Induced by Hyperlipidemia

To study the dose-response effect of lycopene on vessel and neuron damage in the brain against hyperlipidemia, rats were fed with hypercholesterolemic feed and treated with lycopene orally by gavage at the dose of 5, 25, 45, 65, 85, and 105, 125 mg/kg/bw^-1/d^-1. At the end of the fourth week, lycopene doses and serum lycopene concentration showed an inverse U-shape curve. Serum lycopene concentration was negatively correlated with the levels of serum TC, TG, LDL-C, as well as the cerebral LDL-C, VEGF, and VCAM-1. Serum lycopene concentration was positively correlated with the expression of Claudin-5 and the number of neurons in hippocampal CA1 and CA3. Lycopene could also reduce the pathologic change of these areas. These results suggested an inverse U-shape relation between dose and serum concentration of lycopene, and intermediate doses were most effective to protect cerebral vessels and neurons from being damaged by hyperlipidemia.

Different molecular organization of two carotenoids, lutein and zeaxanthin, in human colon epithelial cells and colon adenocarcinoma cells

Two cell lines, human normal colon epithelial cells (CCD 841 CoTr) and human colon adenocarcinoma cells (HT-29) were cultured in the presence of exogenous carotenoids, either zeaxanthin or lutein. Both carotenoids demonstrated cytotoxicity with respect to cancer cells but not to normal cells. Cells from both the cell lines were analyzed with application of fluorescence lifetime imaging microscopy and Raman scattering microscopy. Both imaging techniques show effective incorporation of carotenoid molecules into growing cells. Comparison of the Raman scattering and fluorescence lifetime characteristics reveals different molecular organization of carotenoids in the carcinoma and normal cells. The main difference consists in a carotenoid aggregation level which is substantially lower in the carcinoma cells as compared to the normal cells. Different molecular organization of carotenoids was interpreted in terms of a different metabolism of normal and carcinoma cells and has been concluded to provide a possibility of cancer diagnosis based on spectroscopic analyses.

Rapid and Efficient Conversion of All-E-astaxanthin to 9Z- and 13Z-Isomers and Assessment of Their Stability and Antioxidant Activities

An optimized isomerization method was developed by heating all-E-astaxanthin in ethyl acetate (70 °C) with I-TiO₂ catalyst, yielding 22.7% and 16.9% of 9Z- and 13Z-astaxanthin, respectively, in 2 h, with 92-95% purity after semipreparative HPLC purification. 13Z-Astaxanthin had higher antioxidant activity than all-E- and 9Z-astaxanthins in oxygen radical absorbing capacity assay for lipophilic compounds, photochemiluminescence, and cellular antioxidant activity (CAA) assays, and 9Z-astaxanthin was higher in DPPH radical-scavenging activity assay and lower in CAA assay. All isomers were relatively stable between pH 2.0 and 11.6, except 13Z- and 9Z-astaxanthins at pH 2.0, suggesting they may be converted after passing the gastric phase in vivo. Metal ions did not significantly (p < 0.05) affect the stability. Results of the current study provides a means for further study into the mechanisms related to in vivo transformation and bioavailability of Z-astaxanthins, and their application in the development of functional foods and nutraceutical products.

Temperature dependence of aggregated structure of β-carotene by absorption spectral experiment and simulation

β-carotene can self-assemble to form J- or H-type aggregate in hydrophilic environments, which is crucial for the proper functioning of biological system. Although several ways controlling the formation of the two types of aggregate in hydrated ethanol have been investigated in recent years, our study provided another way to control whether J- or H- β-carotene was formed and presented a method to investigate the aggregated structure. For this purpose, the aggregates of β-carotene formed at different temperatures were studied by UV-Vis spectra and a computational method based on Frenkel exciton was applied to simulate the absorption spectra to obtain the aggregated structure of the β-carotene. The analysis showed that β-carotene formed weakly coupled H-aggregate at 15°C in 1:1 ethanol-water solvent, and with the increase of temperature it tended to form J-type of aggregate. The absorption spectral simulation based on one-dimensional Frenkel exciton model revealed that good fit with the experiment was obtained with distance between neighbor molecules r=0.82nm, disorder of the system D=1500cm(-1) for H-type and r=1.04nm, D=1800cm(-1) for J-type.

Surface-Enhanced Raman and Surface-Enhanced Hyper-Raman Scattering of Thiol-Functionalized Carotene

A thiol-modified carotene, 7'-apo-7'-(4-mercaptomethylphenyl)-β-carotene, was used to obtain nonresonant surface-enhanced Raman scattering (SERS) spectra of carotene at an excitation wavelength of 1064 nm, which were compared with resonant SERS spectra at an excitation wavelength of 532 nm. These spectra and surface-enhanced hyper-Raman scattering (SEHRS) spectra of the functionalized carotene were compared with the spectra of nonmodified β-carotene. Using SERS, normal Raman, and SEHRS spectra, all obtained for the resonant case, the interaction of the carotene molecules with silver nanoparticles, as well as the influence of the resonance enhancement and the SERS enhancement on the spectra, were investigated. The interaction with the silver surface occurs for both functionalized and nonfunctionalized β-carotene, but only the stronger functionalization-induced interaction enables the acquisition of nonresonant SERS spectra of β-carotene at low concentrations. The resonant SEHRS and SERS spectra are very similar. Nevertheless, the SEHRS spectra contain additional bands of infrared-active modes of carotene. Increased contributions from bands that experience low resonance enhancement point to a strong interaction between silver nanoparticles and electronic levels of the molecules, thereby giving rise to a decrease in the resonance enhancement in SERS and SEHRS.

Light-Driven Reconfiguration of a Xanthophyll Violaxanthin in the Photosynthetic Pigment-Protein Complex LHCII: A Resonance Raman Study

Resonance Raman analysis of the photosynthetic complex LHCII, immobilized in a polyacrylamide gel, reveals that one of the protein-bound xanthophylls, assigned as violaxanthin, undergoes light-induced molecular reconfiguration. The phototransformation is selectively observed in a trimeric structure of the complex and is associated with a pronounced twisting and a trans-cis molecular configuration change of the polyene chain of the carotenoid. Among several spectral effects accompanying the reconfiguration there are ones indicating a carotenoid triplet state. Possible physiological importance of the light-induced violaxanthin reconfiguration as a mechanism associated with making the pigment available for enzymatic deepoxidation in the xanthophyll cycle is discussed.

Influence of polar and nonpolar carotenoids on structural and adhesive properties of model membranes

Carotenoids, which are known primarily for their photoprotective and antioxidant properties, may also strongly influence the physical properties of membranes. The localization and orientation of these pigments in the lipid bilayer depends on their structure and is determined by their interactions with lipid molecules. This affects both phase behavior and the mechanical properties of membranes. Differential scanning calorimetry (DSC) and atomic force microscopy (AFM) allowed us to gain a direct insight into the differences between the interaction of the non-polar β-carotene and polar zeaxanthin embedded into DPPC liposomes. DSC results showed that zeaxanthin, having polar ionone rings, interacts more strongly with the membrane lipids than β-carotene. The decrease in molar heat capacity by a factor of 2 with a simultaneous broadening of the main phase transition (gel-to-liquid crystalline phase transition) as compared to the two other systems studied suggests some increased length of the coupled interactions between the polar xanthophyll and lipids. Long-distance interactions lead to the formation of larger clusters which may exhibit higher flexibility than small clusters when only short-distance interactions occur. AFM experiments show that adhesive forces are 2 and 10 times higher for DPPC membranes enriched in β-carotene and zeaxanthin, respectively, than those observed for an untreated system. Temperature dependent measurements of adhesion revealed that subphases can be formed in the gel lamellar state of DPPC bilayers. The presence of the non-polar carotenoid enhanced the effect and even a bifurcation of the substates was detected within a temperature range of 30.0-32.5°C prior to pretransition. It is the first time when the presence of subphases has been demonstrated. This knowledge can be helpful in better understanding the functioning of carotenoids in biological membranes. AFM seem to be a very unique and sensitive method for detecting such fine changes in the lipid bilayers.

Characterizing microbial diversity and damage in mural paintings

Mural paintings are some of the oldest and most important cultural expressions of mankind and play an important role for the understanding of societies and civilizations. These cultural assets have high economic and cultural value and therefore their degradation has social and economic impact. The present work presents a novel microanalytical approach to understand the damages caused by microbial communities in mural paintings. This comprises the characterization and identification of microbial diversity and evaluation of damage promoted by their biological activity. Culture-dependent methods and DNA-based approaches like denaturing gradient gel electrophoresis (DGGE) and pyrosequencing are important tools in the isolation and identification of the microbial communities allowing characterization of the biota involved in the biodeterioration phenomena. Raman microspectrometry, infrared spectrometry, and variable pressure scanning electron microscopy coupled with energy-dispersive X-ray spectrometry are also useful tools for evaluation of the presence of microbial contamination and detection of the alteration products resulting from metabolic activity of the microorganisms. This study shows that the degradation status of mural paintings can be correlated to the presence of metabolically active microorganisms.

Free radical scavenging properties of phytofluene and phytoene isomers as compared to lycopene: a combined experimental and theoretical study

Free radical scavenging properties of Lycopene (LYC), Phytofluene (PF), and Phytoene (PE) are studied experimentally, considering the electron transfer mechanism and using the ABTS(•+) decolouration assay. Density Functional Theory is used to obtain the theoretical UV-visible spectra of ABTS (neutral and cation) and to determine the free radical scavenger capacity in terms of the electron donor mechanism and the deactivation of singlet oxygen. The experimental data agreed very well with the theoretical results. Considering both mechanisms, LYC, PF, and PE can be considered good free radical scavengers, with LYC turning out to be the best and PE the worst antiradical. However, the triplets that formed following the deactivation of singlet oxygen presented similar capacity for donating electrons. In the case of triplets, the antiradical capacity of LYC, PF, and PE is similar in terms of the electron donor mechanism. Although the results indicated that PF and PE are not as effective antiradicals as LYC, which is to be expected due to the number of conjugated double bonds, they do present a higher antioxidant capacity than expected considering the small number of conjugated double bonds.