Carotenoids and β-cyclodextrin inclusion complexes: Raman spectroscopy and theoretical investigation

Fast outdoor screening and discrimination of carotenoids of halophilic microorganisms using miniaturized Raman spectrometers

Eight miniaturized Raman spectrometers were used to perform a fast outdoor screening and discrimination of carotenoids of a series of halophilic and non-halophilic microorganisms on a set of eight lyophilized samples, each containing high concentrations of a specific dominant carotenoid pigment. Raman spectra were acquired using different excitations (532, 785, sequentially shifted excitation of 785 and 853, and 1064 nm), based on the model of each Raman spectrometer, in order to ascertain the feasibility of individual wavelengths. The wavenumber positions of diagnostic Raman bands of carotenoids were observed for the different carotenoid species. Characteristic carotenoid Raman bands of the pigment bacterioruberin were reported (using the 532 nm excitation) at 1504-1509 cm^-1, salinixanthin at 1510-1513 cm^-1, spirilloxanthin at 1509-1513 cm^-1, decaprenoxanthin at 1519 cm^-1, β-carotene at 1526 cm^-1, and sarcinaxanthin at 1526-1528 cm^-1. A 532 nm excitation consistently provided best results due to the significant resonance signal enhancement (both quantitative and qualitative carotenoid detection). Good results were also obtained using the sequentially shifted excitation combining two lasers in the near infrared spectral region, and similarly good results were acquired using a standard 1064 nm excitation. The least suitable was a 785 nm excitation, with the carotenoid Raman signal almost always weaker compared to major fluorescence signal arising from other types of pigments or biomolecules in the samples. A thorough light shielding was essential in order to acquire good quality data. This study shows that miniaturized Raman spectrometers, some even equipped with longer wavelength excitation, are able to detect different carotenoid pigments under non-laboratory conditions in a fast way, and discriminate between them, to a certain degree. The implications of this type of research are especially useful in astrobiology, where the searching, detection and discrimination of biomarkers such as carotenoids is receiving significant attention.

Utilizing Raman Spectroscopy as a Tool for Solid- and Solution-Phase Analysis of Metalloorganic Cage Host-Guest Complexes

The host-guest chemistry of coordination cages continues to promote significant interest, not least because confinement effects can be exploited for a range of applications, such as drug delivery, sensing, and catalysis. Often a fundamental analysis of noncovalent encapsulation is required to provide the necessary insight into the design of better functional systems. In this paper, we demonstrate the use of various techniques to probe the host-guest chemistry of a novel Pd₂L₄ cage, which we show is preorganized to selectively bind dicyanoarene guests with high affinity through hydrogen-bonding and other weak interactions. In addition, we exemplify the use of Raman spectroscopy as a tool for analyzing coordination cages, exploiting alkyne and nitrile reporter functional groups that are contained within the host and guest, respectively.

Kinetic Study of Encapsulated β-Carotene Degradation in Dried Systems: A Review

β-Carotene serves as a precursor of vitamin A and provides relevant health benefits. To overcome the low bioavailability of β-carotene from natural sources, technologies have been designed for its encapsulation in micro- and nano-structures followed by freeze-drying, spray-drying, supercritical fluid-enhanced dispersion and electrospraying. A technological challenge is also to increase β-carotene stability, since due to its multiple conjugated double bonds, it is particularly prone to oxidation. This review analyzes the stability of β-carotene encapsulated in different dried micro- and nano-structures by comparing rate constants and activation energies of degradation. The complex effect of water activity and glass transition temperature on degradation kinetics is also addressed, since the oxidation process is remarkably dependent on the glassy or collapsed state of the matrix. The approaches to improve β-carotene stability, such as the development of inclusion complexes, the improvement of the performance of the interface between air and oil phase in which β-carotene was dissolved by application of biopolymer combinations or functionalization of natural biopolymers, the addition of hydrophilic small molecular weight molecules that reduce air entrapped in the powder and the co-encapsulation of antioxidants of various polarities are discussed and compared, in order to provide a rational basis for further development of the encapsulation technologies.

An Optimization Procedure for Preparing Aqueous CAR/HP-CD Aggregate Dispersions

β-Carotene is a very important molecule for human health. It finds a large application in the food industry, especially for the development of functional foods and dietary supplements. However, β-carotene is an unstable compound and is sensitive to light, temperature, and oxygen. To overcome those limitations, various delivery systems were developed. The inclusion of β-carotene by cyclodextrin aggregates is attractive due to non-toxicity, low hygroscopicity, stability, and the inexpensiveness of cyclodextrins. In this study, β-carotene/2-hydroxypropyl-β-cyclodextrin aggregates were prepared based on the procedure of the addition of β-carotene in an organic solvent to the hot water dispersion of 2-hydroxypropyl-β-cyclodextrin and the following instant evaporation of the organic solvent. The best conditions for the aggregate preparation were found to be as follows: 25% concentration of 2-hydroxypropyl-β-cyclodextrin in water, 65 °C temperature, and acetone for β-carotene dissolution. The efficiency of entrapping was equal to 88%. The procedure is attractive due to the short time of the aggregate preparation.

Proving Nanoscale Chiral Interactions of Cyclodextrins and Propranolol Enantiomers by Means of SERS Measurements Performed on a Solid Plasmonic Substrate

Chiral separation is an important issue for the pharmaceutical industry. Over the years, several separation methods have been developed, mainly based on chromatography. Their working principle is based on the formation of transient diastereoisomers, but the very subtle nanoscale interactions responsible for separation are not always understood. Recently, Raman and surface-enhanced Raman (SERS) spectroscopy have provided promising results in this field. Here we present Raman/SERS experimental data that provide useful information concerning the nanoscale interactions between propranolol enantiomers and α, β, and γ cyclodextrins. Raman spectroscopy was used to prove the formation of host–guest intermolecular complexes having different geometries of interaction. The occurrence of new vibrational bands and a change in the intensities of others are direct proofs of complexes’ formation. These observations were confirmed by DFT calculations. By performing SERS measurements on a new type of plasmonic substrate, we were able to prove the intermolecular interactions responsible for PRNL discrimination. It turned out that the interaction strength between the substrate and the intermolecular complexes is of paramount importance for SERS-based chiral discrimination. This approach could represent a very good starting point for the evaluation of molecular interactions manifesting between other pharmaceutical compounds and different classes of chiral selectors.

Structure elucidation of the novel carotenoid gemmatoxanthin from the photosynthetic complex of Gemmatimonas phototrophica AP64

Gemmatimonas phototrophica AP64 is the first phototrophic representative of the bacterial phylum Gemmatimonadetes. The cells contain photosynthetic complexes with bacteriochlorophyll a as the main light-harvesting pigment and an unknown carotenoid with a single broad absorption band at 490 nm in methanol. The carotenoid was extracted from isolated photosynthetic complexes, and purified by liquid chromatography. A combination of nuclear magnetic resonance (1H NMR, COSY, 1H-13C HSQC, 1H-13C HMBC, J-resolved, and ROESY), high-resolution mass spectroscopy, Fourier-transformed infra-red, and Raman spectroscopy was used to determine its chemical structure. The novel linear carotenoid, that we have named gemmatoxanthin, contains 11 conjugated double bonds and is further substituted by methoxy, carboxyl and aldehyde groups. Its IUPAC-IUBMB semi-systematic name is 1'-Methoxy-19'-oxo-3',4'-didehydro-7,8,1',2'-tetrahydro- Ψ, Ψ carotene-16-oic acid. To our best knowledge, the presence of the carboxyl, methoxy and aldehyde groups on a linear C40 carotenoid backbone is reported here for the first time.

Encapsulation of Carotenoids as Food Colorants via Formation of Cyclodextrin Inclusion Complexes: A Review

The use of natural carotenoids as food colorants is an important trend of innovation in the industry due to their low toxicity, their potential as bio-functional ingredients, and the increasing demand for natural and organic foods. Despite these benefits, their inclusion in food matrices presents multiple challenges related to their low stability and low water solubility. The present review covers the main concepts and background of carotenoid inclusion complex formation in cyclodextrins as a strategy for their stabilization, and subsequent inclusion in food products as color additives. The review includes the key aspects of the molecular and physicochemical properties of cyclodextrins as complexing agents, and a detailed review of the published evidence on complex formation with natural carotenoids from different sources in cyclodextrins, comparing complex formation methodologies, recovery, inclusion efficiency, and instrumental characterization techniques. Moreover, process flow diagrams (PFD), based on the most promising carotenoid-cyclodextrin complex formation methodologies reported in literature, are proposed, and discussed as a potential tool for their future scale-up. This review shows that the inclusion of carotenoids in complexes with cyclodextrins constitutes a promising technology for the stabilization of these pigments, with possible advantages in terms of their stability in food matrices.

Molecular Structure of Cefuroxime Axetil Complexes with α-, β-, γ-, and 2-Hydroxypropyl-β-Cyclodextrins: Molecular Simulations and Raman Spectroscopic and Imaging Studies

The formation of cefuroxime axetil+cyclodextrin (CA+CD) complexes increases the aqueous solubility of CA, improves its physico-chemical properties, and facilitates a biomembrane-mediated drug delivery process. In CD-based tablet formulations, it is crucial to investigate the molecular details of complexes in final pharmaceutical preparation. In this study, Raman spectroscopy and mapping were applied for the detection and identification of chemical groups involved in α-, β-, γ-, and 2-hydroxypropyl-β-CD (2-HP- β-CD)+CA complexation process. The experimental studies have been complemented by molecular dynamics-based investigations, providing additional molecular details of CA+CD interactions. It has been demonstrated that CA forms the guest–host type inclusion complexes with all studied CDs; however, the nature of the interactions is slightly different. It seems that both α- and β-CD interact with furanyl and methoxy moieties of CA, γ-CD forms a more diverse pattern of interactions with CA, which are not observed in other CDs, whereas 2HP-β-CD binds CA with the contribution of hydrogen bonding. Apart from supporting this interpretation of the experimental data, molecular dynamics simulations allowed for ordering the CA+CD binding affinities. The obtained results proved that the molecular details of the host–guest complexation can be successfully predicted from the combination of Raman spectroscopy and molecular modeling.

Quantum chemical investigation of beta-CD–catechin flavonoid encapsulation in solution through NMR analysis: an adequate controlled drug-delivery system

DFT–PCM–water calculations of ¹H NMR chemical shifts for 28 optimized catechin–beta-CD complex structures revealed that adsorption mode of complexion should be predominant in aqueous media, with full-inclusion 1 : 1 structure being in total disagreement with experimental ¹H NMR profile (D₂O).

The Diversity of Linear Conjugated Polyenes and Colours in Nature: Raman Spectroscopy as a Diagnostic Tool

This review is centered on the linear conjugated polyenes, which encompasses chromatic biomolecules, such as carotenoids, polyunsaturated aldehydes and polyolefinic fatty acids. The linear extension of the conjugated double bonds in these molecules is the main feature that determines the spectroscopic properties as light-absorbing. These classes of compounds are responsible for the yellow, orange, red and purple colors which are observed in their parent flora and fauna in nature. Raman spectroscopy has been used as analytical tool for the characterization of these molecules, mainly due to the strong light scattering produced by the delocalized pi electrons in the carbon chain. In addition, conjugated polyenes are one of the main target molecular species for astrobiology, and we also present a brief discussion of the use of Raman spectroscopy as one of the main analytical tools for the detection of polyenes extra-terrestrially.

The characterization and evaluation of the synthesis of large-ring cyclodextrins (CD9-CD22) and α-tocopherol with enhanced thermal stability

Large-ring cyclodextrins LR-CDs (CD₉–CD₂₂) were obtained from rice starch using cyclodextrin glycosyltransferase (CGTase), and were used as a wall material for embedding α-tocopherol. Complexes of α-tocopherol and LR-CDs were prepared by co-precipitation. A molar ratio of α-tocopherol/LR-CD of 1 : 2 showed the highest encapsulation efficiency. The surface morphology of the complex particles was observed to vary from irregular flakes to the formation of smaller clusters of particles using scanning electron microscopy (SEM). Based on ¹H NMR and FT-IR observations, the inclusion complexes exhibited significant chemical shifts of 0.3 ppm and decreased peak signals. In addition, thermal analysis showed that the microcapsules improved the thermostability of the α-tocopherols. Antioxidant activity analysis proved the stability of α-tocopherol during storage. This study could serve as a reference for the more effective use of LR-CDs as wall materials.

Large-ring cyclodextrins LR-CDs (CD₉–CD₂₂) were obtained from rice starch using cyclodextrin glycosyltransferase (CGTase), and were used as a wall material for embedding α-tocopherol.

A Spectroscopic Study of Solid-Phase Chitosan/Cyclodextrin-Based Electrospun Fibers

In this study, chitosan (chi)/hydroxypropyl-β-cyclodextrin (HPCD) 2:20 and 2:50 Chi:HPCD fibers were assembled via an electrospinning process that contained a mixture of chitosan and HPCD with trifluoroacetic acid (TFA) as a solvent. Complementary thermal analysis (thermal gravimetric analysis (TGA)/differential scanning calorimetry (DSC)) and spectroscopic methods (Raman/IR/NMR) were used to evaluate the structure and composition of the fiber assemblies. This study highlights the multifunctional role of TFA as a solvent, proton donor and electrostatically bound pendant group to chitosan, where the formation of a ternary complex occurs via supramolecular host–guest interactions. This work contributes further insight on the formation and stability of such ternary (chitosan + HPCD + solvent) electrospun fibers and their potential utility as “smart” fiber coatings for advanced applications.

Structural diversity in the host-guest complexes of the antifolate pemetrexed with native cyclodextrins: gas phase, solution and solid state studies

The complexation of the antifolate pemetrexed (PTX) with native cyclodextrins was studied. This process, along with the findings gathered for the structurally related folic acid was treated as a model for exploiting host–guest interactions of this class of guest molecules in the gas phase, in solution and in the solid state. Mass spectrometry was employed for the investigation of the architecture and relative gas-phase stabilities of these supramolecular complexes. The mode of complexation was further tracked by 1D and 2D NMR proving the formation of the exclusion-type complex with α-CD and pseudorotaxane inclusion-type complexes with β-, and γ-CDs. UV–vis titrations at pH 7.4 gave association constants for the obtained complexes. The stability of the complexes increases in the series: α-CD/PTX < γ-CD/PTX << β-CD/PTX. The association of PTX with a monomer cyclodextrin equivalent – methyl α-D-glucopyranoside – was investigated for a deeper understanding of the type of host–guest interactions. Solid state studies of PTX/CDs were performed using FTIR–ATR and Raman spectroscopy techniques.

Stimulus-responsive light-harvesting complexes based on the pillararene-induced co-assembly of β-carotene and chlorophyll

The locations and arrangements of carotenoids at the subcellular level are responsible for their designated functions, which reinforces the necessity of developing methods for constructing carotenoid-based suprastructures beyond the molecular level. Because carotenoids lack the binding sites necessary for controlled interactions, functional structures based on carotenoids are not easily obtained. Here, we show that carotene-based suprastructures were formed via the induction of pillararene through a phase-transfer-mediated host-guest interaction. More importantly, similar to the main component in natural photosynthesis, complexes could be synthesized after chlorophyll was introduced into the carotene-based suprastructure assembly process. Remarkably, compared with molecular carotene or chlorophyll, this synthesized suprastructure exhibits some photocatalytic activity when exposed to light, which can be exploited for photocatalytic reaction studies of energy capture and solar conversion in living organisms.

Gold nanoparticles interacting with β-cyclodextrin-phenylethylamine inclusion complex: a ternary system for photothermal drug release

We report the synthesis of a 1:1 β-cyclodextrin-phenylethylamine (βCD-PhEA) inclusion complex (IC) and the adhesion of gold nanoparticles (AuNPs) onto microcrystals of this complex, which forms a ternary system. The formation of the IC was confirmed by powder X-ray diffraction and NMR analyses ((1)H and ROESY). The stability constant of the IC (760 M(-1)) was determined using the phase solubility method. The adhesion of AuNPs was obtained using the magnetron sputtering technique, and the presence of AuNPs was confirmed using UV-vis spectroscopy (surface plasmon resonance effect), which showed an absorbance at 533 nm. The powder X-ray diffractograms of βCD-PhEA were similar to those of the crystals decorated with AuNPs. A comparison of the one- and two-dimensional NMR spectra of the IC with and without AuNPs suggests partial displacement of the guest to the outside of the βCD due to attraction toward AuNPs, a characteristic tropism effect. The size, morphology, and distribution of the AuNPs were analyzed using TEM and SEM. The average size of the AuNPs was 14 nm. Changes in the IR and Raman spectra were attributed to the formation of the complex and to the specific interactions of this group with the AuNPs. Laser irradiation assays show that the ternary system βCD-PhEA-AuNPs in solution enables the release of the guest.

Study of carotenoids in cyanobacteria by Raman spectroscopy

Cyanobacteria have established dominant aquatic populations around the world, generally in aggressive environments and under severe stress conditions, e.g., intense solar radiation. Several marine strains make use of compounds such as the polyenic molecules for their damage protection justifying the range of colours observed for these species. The peridinin/chlorophyll-a/protein complex is an excellent example of essential structures used for self-prevention; their systems allow to them surviving under aggressive environments. In our simulations, few protective dyes are required to the initial specimen defense; this is an important data concern the synthetic priority in order to supply adequate damage protection. Raman measurements obtained with 1064 and 514.5 nm excitations for Cylindrospermopsis raciborskii and Microcystis aeruginosa strains shows bands assignable to the carotenoid peridinin. It was characterized by bands at 1940, 1650, 1515, 1449, 1185, 1155 and 1000 cm(-1) assigned to ν(C=C=C) (allenic vibration), ν(C=C/CO), ν(C=C), δ(C-H, C-18/19), δ(C-H), ν(C-C), and ρ(C-CH3), respectively. Recognition by Raman spectroscopy proved to be an important tool for preliminaries detections and characterization of polyene molecules in several algae, besides initiate an interesting discussion about their synthetic priority.

Water soluble biocompatible vesicles based on polysaccharides and oligosaccharides inclusion complexes for carotenoid delivery

Since carotenoids are highly hydrophobic, air- and light-sensitive hydrocarbon compounds, developing methods for increasing their bioavailability and stability towards irradiation and reactive oxygen species is an important goal. Application of inclusion complexes of "host-guest" type with polysaccharides and oligosaccharides such as arabinogalactan, cyclodextrins and glycyrrhizin minimizes the disadvantages of carotenoids when these compounds are used in food processing (colors and antioxidant capacity) as well as for production of therapeutic formulations. Cyclodextrin complexes which have been used demonstrated enhanced storage stability but suffered from poor solubility. Polysaccharide and oligosaccharide based inclusion complexes play an important role in pharmacology by providing increased solubility and stability of lipophilic drugs. In addition they are used as drug delivery systems to increase absorption rate and bioavailability of the drugs. In this review we summarize the existing data on preparation methods, analysis, and chemical reactivity of carotenoids in inclusion complexes with cyclodextrin, arabinogalactan and glycyrrhizin. It was demonstrated that incorporation of carotenoids into the "host" macromolecule results in significant changes in their physical and chemical properties. In particular, polysaccharide complexes show enhanced photostability of carotenoids in water solutions. A significant decrease in the reactivity towards metal ions and reactive oxygen species in solution was also detected.

Analytical techniques for characterization of cyclodextrin complexes in the solid state: A review

Cyclodextrins are cyclic oligosaccharides able to form inclusion complexes with a variety of hydrophobic guest molecules, positively modifying their physicochemical properties. A thorough analytical characterization of cyclodextrin complexes is of fundamental importance to provide an adequate support in selection of the most suitable cyclodextrin for each guest molecule, and also in view of possible future patenting and marketing of drug-cyclodextrin formulations. The demonstration of the actual formation of a drug-cyclodextrin inclusion complex in solution does not guarantee its existence also in the solid state. Moreover, the technique used to prepare the solid complex can strongly influence the properties of the final product. Therefore, an appropriate characterization of the drug-cyclodextrin solid systems obtained has also a key role in driving in the choice of the most effective preparation method, able to maximize host-guest interactions. The analytical characterization of drug-cyclodextrin solid systems and the assessment of the actual inclusion complex formation is not a simple task and involves the combined use of several analytical techniques, whose results have to be evaluated together. The objective of the present review is to present a general prospect of the principal analytical techniques which can be employed for a suitable characterization of drug-cyclodextrin systems in the solid state, evidencing their respective potential advantages and limits. The applications of each examined technique are described and discussed by pertinent examples from literature.

Raman spectroscopy as a tool in differentiating conjugated polyenes from synthetic and natural sources

This work presents the Raman spectroscopic characterization of synthetic analogs of natural conjugated polyenals found in octocorals, focusing the unequivocal identification of the chemical species present in these systems. The synthetic material was produced by the autocondensation reaction of crotonaldehyde, generating a demethylated conjugated polyene containing 11 carbon-carbon double bonds, with just a methyl group on the end of the carbon chain. The resonance Raman spectra of such pigment has shown the existence of enhanced modes assigned to ν₁(CC) and ν₂(CC) modes of the main chain. For the resonance Raman spectra of natural pigments from octocorals collected in the Brazilian coast, besides the previously cited bands, it could be also observed the presence of the ν₄(CCH₃), related to the vibrational mode who describes the vibration of the methyl group of the central carbon chain of carotenoids. Other interesting point is the observation of overtones and combination bands, which for carotenoids involves the presence of the ν₄ mode, whereas for the synthetic polyene this band, besides be seen at a slightly different wavenumber position, does not appear as an enhanced mode and also as a combination, such as for the natural carotenoids. Theoretical molecular orbital analysis of polyenal-11 and lycopene has shown the structural differences which are also responsible for the resonance Raman data, based on the appearance of the (CH3) vibrational mode in the resonant transition only for lycopene. At last, the Raman band at ca. 1010 cm(-1), assigned to the (CH₃) vibrational mode, can be used for attributing the presence of each one of the conjugated polyenes: the resonance Raman spectrum containing the band at ca. 1010 cm(-1) refers to the carotenoid (in this case lycopene), and the absence of such band in resonance conditions refers to the polyenal (in this case the polyenal-11).

Conjugated polyenes as chemical probes of life signature: use of Raman spectroscopy to differentiate polyenic pigments

Polyenes, which are represented by carotenes, carotenoids and conjugated polyenals, are some of the most important targets for astrobiology, because they can provide strong evidence of the presence of organic compounds in the most extreme environments, such as on Mars. Raman spectroscopy has been used as the main analytical tool in the identification of such compounds, for the greatest variety of living species, from microorganisms to animals and plants. However, using only the position of the characteristic Raman bands can lead to errors in tentatively identifying chemicals. In this work, we present a series of observations that can provide a more complete and robust way to analyse the Raman spectrum of a polyenal, in which the position, the intensity, the use of various laser lines for excitation, and the combination of more than one pigment can be considered in the complete analysis.

Spectroscopic studies of R(+)-α-lipoic acid--cyclodextrin complexes

α-Lipoic acid (ALA) has a chiral center at the C6 position, and exists as two enantiomers, R(+)-ALA (RALA) and S(−)-ALA (SALA). RALA is naturally occurring, and is a cofactor for mitochondrial enzymes, therefore playing a major role in energy metabolism. However, RALA cannot be used for pharmaceuticals or nutraceuticals because it readily polymerizes via a 1,2-dithiolane ring-opening when exposed to light or heat. So, it is highly desired to find out the method to stabilize RALA. The purpose of this study is to provide the spectroscopic information of stabilized RALA and SALA through complexation with cyclodextrins (CDs), α-CD, β-CD and γ-CD and to examine the physical characteristics of the resultant complexes in the solid state. The RALA-CD structures were elucidated based on the micro fourier transform infrared (FT-IR) and Raman analyses. The FT-IR results showed that the C=O stretching vibration of RALA appeared at 1717 cm⁻¹ and then shifted on formation of the RALA-CD complexes. The Raman spectra showed that the S–S and C–S stretching vibrations for RALA at 511 cm⁻¹ (S–S), 631 cm⁻¹ (C–S) and 675 cm⁻¹ (C–S) drastically weakened and almost disappeared upon complexation with CDs. Several peaks indicative of O–H vibrations also shifted or changed in intensity. These results indicate that RALA and CDs form host-guest complexes by interacting with one another.

Raman spectroscopy as a tool for polyunsaturated compound characterization in gastropod and limnic terrestrial shell specimens

The colours of mollusc shells were determined using the Raman spectroscopy and these analyses suggest that the conjugated polyenes (carotenoids) and psittacofulvins are the organic pigments incorporated into their skeletal structures responsible by their colorations. The symmetric stretching vibration of the carbonate ion gives rise to a very strong Raman band at ca. 1089 cm(-1) and a weak band at 705 cm(-1), for all samples; the second band characterizes the aragonite as the inorganic matrix and can be used as a marker. The specimens show bands at 1523-1500 and at 1130-1119 cm(-1), assigned to the ν1 and ν2 modes of the polyenic chain vibrations, respectively. Another band at 1293 cm(-1), assigned to the CH=CH in-plane rocking mode of the olefinic hydrogen is also observed in all samples, which reinforces the psittacofulvin compound as the main pigment present in the analyzed samples.

Inclusion complexes of red bell pepper pigments with β-cyclodextrin: preparation, characterisation and application as natural colorant in yogurt

This work aimed to prepare inclusion complexes between red bell pepper pigments and β-cyclodextrin using two different procedures (i.e., magnetic stirring and ultrasonic homogenisation), to characterise the prepared inclusion complexes and to evaluate the colour stability of a selected complex added to yogurt. The mass ratio of extract to β-cyclodextrin was 1:4. The formed extract: β-cyclodextrin complexes and a physical mixture of extract and β-cyclodextrin were evaluated by differential scanning calorimetry, Fourier transform-infrared spectroscopy, proton nuclear magnetic resonance, particle size distribution and Zeta potential. The obtained data showed that ultrasonic homogenisation resulted in better yield and inclusion efficiency compared to magnetic stirring. The yogurt with the added complex produced by ultrasonic homogenisation showed slower variations for the a(∗) (redness) and b(∗) (yellowness) indices compared to yogurt with added extract, indicating a higher protection of the colour during storage.