Carrageenan Molecules Research Articles

Effect of amphiphilic compounds on the thermoreversible conformational transition of κ carrageenan in aqueous-saline solutions

The effect of amino acids, phenylalanine and lysine, and lithium ions on the conformation state of κ carrageenan has been studied by high-sensitivity DSC. The binding constants of lysine and lithium ions with the helical and coil forms of polysaccharide have been measured. The preferential binding of lysine molecules and lithium ions by the helical conformation of κ carrageenan has been demonstrated. The affinity of the helical form of κ carrageenan to lysine is much higher than that to lithium ions. The conformational state of κ carrageenan in the presence of cetyltrimethylammonium bromide has been investigated. The binding of cetyltrimethylammonium by κ carrageenan molecules leads to development of a new ordered structure of the polysaccharide.

Irreversible Thermal Denaturation of β-Lactoglobulin Retards Adsorption of Carrageenan onto β-Lactoglobulin-Coated Droplets

The influence of isothermal heat treatments on the adsorption of anionic carrageenan molecules to the surfaces of anionic beta-lactoglobulin-coated droplets has been investigated. The zeta-potential, mean particle diameter, microstructure, and creaming stability of emulsions containing beta-lactoglobulin-coated droplets and/or carrageenan molecules that had previously been heat treated at temperatures ranging from 30 to 90 degrees C for 20 min were measured (pH 6.0, 150 mM NaCl). Three different heat treatments were used to establish the physicochemical origin of the influence of thermal history on the adsorption of carrageenan molecules to the protein coated droplets: (i) droplets and carrageenan were mixed at room temperature, then heated together; (ii) droplets were heated, cooled to room temperature, then mixed with carrageenan; (iii) carrageenan was heated, cooled to room temperature, then mixed with droplets. For treatments i and ii appreciably more carrageenan adsorbed to the protein-coated droplet surfaces at temperatures < or = 60 degrees C than at higher temperatures. For treatment iii, carrageenan adsorbed to the droplet surfaces across the whole temperature range. These results suggest that an irreversible thermal denaturation of the adsorbed beta-lactoglobulin molecules inhibited the adsorption of carrageenan molecules to the droplet surfaces. We postulate that there is a patch of positive charge on the surface of the native globular protein molecules which becomes more diffuse upon thermal denaturation. We found that the carrageenan molecules were unable to protect the beta-lactoglobulin-coated droplets at high temperatures (T > 60 degrees C) because they desorbed from the droplet surfaces. Nevertheless, adsorption of iota-carrageenan was capable of protecting the droplets against flocculation caused by surface denaturation of the adsorbed proteins at lower temperatures (T < or = 50 degrees C).

The effect of the linear charge density of carrageenan on the ion binding investigated by differential scanning calorimetry, dc conductivity, and kHz dielectric relaxation

The effect of the linear charge density of natural polyelectrolyte, carrageenan, on the ion binding to carrageenan molecules in relation to the gelation was investigated by using the dielectric relaxation spectroscopy, dc conductivity, optical rotation, and differential scanning calorimetry (DSC). Although carrageenan is an anionic polysaccharide, carrageenan molecules in the helix state at low temperatures can bind not only cation, such as potassium and cesium, but also anion, such as iodide. The dc conductivity steeply decreases just below the coil–helix transition temperature, which indicates the binding of ion to the carrageenan molecules in the helix state due to the increase of the linear charge density compared with that in the coil state. The addition of NaI promotes the helix formation, and prevents from aggregation of helices, which was suggested by the results of the dynamic shear modulus and the DSC, and resulted in an increase of the relaxation amplitude of the lowest frequency relaxation (∼kHz) attributed to the fluctuation of the tightly bound counter ions along the high charge density region (helix). It is concluded that binding of iodide induces (1) the increase in the amount of tightly bound counterions to carrageenan molecules and (2) the formation of non-aggregated helix.

SANS study of surfactant ordering in κ-carrageenan/cetylpyridinium chloride complexes

Small-angle neutron scattering using contrast variation by H2O/D2O has been applied for the structural investigation of κ-carrageenan/cetylpyridinium chloride (CPC) complexes. Interaction of κ-carrageenan with an ionic surfactant involves self-assembly of the surfactant molecules in conjunction with the carrageenan molecules and the formation of an ordered structure. Contrast matching conditions for the polysaccharide (70% H2O/30% D2O) allowed to obtain the small-angle scattering pattern from the surfactant part of the complexes. The SANS curves reveal that the observed scattering heterogeneities represent regions with sharp phase boundaries. From the Guinier part of the scattering curves, the size of these regions is determined. The obtained values are in good agreement with the structural characteristics of the κ-carrageenan/CPC complexes determined independently by SAXS and SANS from the position and the half-width of the Braggs peaks of the scattering patterns.

Structural investigations of carrageenan-surfactant systems by synchrotron X-ray scattering

Small-angle X-ray scattering by means of synchrotron radiation was used to study the interaction of κ- and ι-carrageenan of different molar mass in the presence of the gel-inducing ions, K', with the ionic surfactants cetylpyridinium chloride (CPC) and dodecylpyridinium chloride (DPC). This interaction resulted in a more or less complete shrinking of the gel and in the formation of ordered periodic structures of the surfactant in conjunction with the carrageenan molecules. The influence of the polymer concentration for a given surfactant concentration, the content of surfactant for the same concentration of the polysaccharide, the molar mass, and the linear charge density of the polymer were all investigated. Decreasing the length of the alkyl chain of the surfactant, increasing the charge density of the polymer chain, and increasing the polymer concentration for the samples explored improved the ordering in the carrageenan-surfactant complexes. The structures of the K-carrageenan-CPC complexes were investigated as a function of temperature during reversible heating-cooling cycles, and it was shown that the addition of the surfactant lead to a more pronounced temperature stability of polymer network.

The influence of locust bean gum and dextran on the gelation of κ-carrageenan

The interaction of κ-carrageenan with locust bean gum and dextran has been studied by rheology, differential scanning calorimetry (DSC), and electron spin resonance spectroscopy (ESR). Rheological measurements show that the carrageenan gel characteristics are greatly enhanced in the presence of locust bean gum but not in the presence of dextran. Carrageenan/locust bean gum mixtures show two peaks in the dsc cooling curves. The higher temperature peak corresponds to the temperature of gelation and its intensity increases at the expense of the lower temperature peak as the proportion of locust bean gum in the mixture increases. Furthermore, the DSC heating curves show enhanced broadening when locust bean gum is present, indicating increased aggregation. These results are taken as evidence of carrageenan/locust bean gum association. The gelation process has also been followed by ESR using spin-labeled carrageenan. On cooling carrageenan solutions, an immobile component appears in the ESR spectra signifying a loss of segmental mobility consistent with chain stiffening due to the coil → helix conformational transition and helix aggregation. For carrageenan/locust bean gum mixtures, carrageenan ordering occurs at temperatures corresponding to the higher temperature DSC setting peak and the temperature of gelation. Similar studies using spin-labeled locust bean gum show that its mobility remains virtually unaffected during the gelation process. It is evident, therefore, that carrageenan and locust bean gum interact only weakly. It is proposed that at low carrageenan concentrations the gel network consists of carrageenan helices cross-linked by locust bean gum chains. At high carrageenan concentrations the network is enhanced by the additional self-aggregation of the “excess” carrageenan molecules. For carrageenan/dextran mixtures, only one peak is observed in the dsc cooling curves. The onset of gelation shifts to higher temperatures only at very high (20%) dextran concentrations and this is attributed to volume exclusion effects. Furthermore, there is no enhanced broadening of the peaks in the DSC heating curves as for the carrageenan/locust bean gum systems. It is therefore concluded that carrageenan/dextran association does not occur. The difference in behavior between locust bean gum and dextran is attributed to the greater flexibility of the dextran chains. © 1996 John Wiley & Sons, Inc.

The effect of charge density and conformation on the polyelectrolyte complex formation between carrageenan and chitosan

The formation of polyelectrolyte complexes (PECs) between chitosan varying in degree of deacetylation (DD) and κ-, ι- and λ-carrageenan, respectively, was investigated, in moderately concentrated solutions, with emphasis on the effect of charge density and conformation. Results obtained indicate that macroscopically electroneutral PECs were formed when chitosan interacted with carrageenan molecules in coil or non-aggregated helical conformation. When the κ-carrageenan existed in an aggregated helical conformation the interaction with chitosan produced PECs with a charge ratio of chitosan to carrageenan below unity. Furthermore, the PEC formation process proved to be significantly affected by the presence of low molecular weight polyelectrolyte components.

Acid Hydrolysis of K‐Carrageenan in a Batch Reactor: Stochastic Simulation of Change of Molecular Weight Distribution with Time

AbstractThe degradation of K‐carrageenan by acid hydrolysis in a LiCl/HCl (pH 2) buffer solution has been studied at various temperatures in a batch reactor. The reduction in the weight‐average molecular weight and the variation in the molecular weight distribution (MWD) have been followed over time by an SEC‐MALLS‐RI chromatography system. While a deterministic rate equation can be fit to the average molecular weight‐time data, this is not the case for the MWD‐time data. Since depolymerization by hydrolysis usually proceeds via nonspecific (random) bond cleavage, a stochastic approach can be appropriate for the resultant MWD‐time data. In the present work, the master equation has been derived from the stochastic population balance for this batch hydrolysis system characterized by a set of discrete states, each representing a particular molecular weight range. The governing equations for the means, variances, and covariances of the random variables, each representing the number of carrageenan molecules in an individual state, have been extracted from the master equation. The equations for the means have been applied to the MWD‐reaction time data, and the unknown reaction rate parameters have been estimated. These parameters can be used to generate the MWD at any hydrolysis reaction time from any initial MWD. The applicability, limitations, advantages, and sources of error of the derived model have been discussed.

Effect of pressure on the sol-gel transition of carrageenans

The effects of pressure on the sol-gel transition of κ- and ι-carrageenans were studied in KCl solutions under high pressures up to 3000 kg/cm 2. The carrageenan gels were destabilized by pressure: the pressure depression of melting temperature, ( dT/ dP) m , was −5.7 × 10 −3 and −4.0 × 10 −3 K cm 2/kg independent of KCl concentration for κ- and ι-carrageenans, respectively. The enthalpy, entropy and volume changes accompanying the gel formation were calculated from the Eldridge-Ferry's plots and the Clausius-Clapeyron equation. The volume change per unit cross-link (two disaccharide residues) was estimated to be (2.5 ∼ 4.9) and (1.7 ∼ 3.4) ml/mol for κ- and ι-carrageenans, respectively. The compressibility of both carrageenan molecules appeared to be larger by (1.6 ∼ 2.6) × 10 −12 (κ-form) and by (0.8 ∼ 1.3) × 10 −12 cm 2/ dyn (i-form) in gel state as compared with in sol state These increases in volume and compressibility on gelation were attributed to a reduction of water of hydration from the carrageenan molecules, which is mainly due to a replacement of the polymer-water hydrogen bond by the polymer-polymer hydrogen bond. These results seemed not inconsistent with the idea that a double helix structure of carrageenan gels may persist in solution as well as in the solid state.

Carrageenans in the cell walls of Chondrus crispus Stack. (Rhodophyceae, Gigartinales) II. Birefringence

Positive values of intrinsic birefringence were obtained with respect to circumferential directions in the cell walls of fixed but unstained sections of Chondrus crispus. With respect to the same directions, negative values of birefringence were obtained in sections stained with toluidine blue (the ‘topooptical reaction’). These results suggest that the carrageenan occurring in the walls contributes to their intrinsic birefringence, and that the orientation of the carrageenan molecules in the cell walls is similar to that of the microfibrilsseen by electron microscopy, i.e. parallel to the surface of the wall, but random in face view.The intrinsic birefringence of the cortical and subcortical intercellular matrix was positive, and the topooptical reaction negative, with respect to the direction of the cell rows. Cortical and subcortical birefringence in the tetrasporophyte is more extensive than that in the female gametophyte. This difference may be used to differentiate the nuclear phase of non-reproductive plants.

Carrageenan: The effect of molecular weight and polymer type on its uptake, excretion and degradation in animals

A variety of τ-, κ- and λ-carrageenans was given to guinea-pigs, monkeys and rats, either in the drinking-water, by gavage or in the diet. Faecal and liver samples were examined qualitatively by gel electrophoresis, to determine any changes in the apparent molecular weight of carrageenans after administration. Quantitative measurements of carrageenans were carried out on samples of liver and urine. That there was little or no absorption of carrageenans of high molecular weight was evidenced by the absence of carrageenan from the livers of guinea-pigs or rats or from the urine of guinea-pigs or monkeys. By contrast, substantial amounts of carrageenan were found in the livers of guinea-pigs and rats given low-molecular-weight carrageenans (M n ⩽ 40,000). Intermediate amounts of carrageenan were found in livers of animals given carrageenans ranging in M n between 40,000 and 150,000. Urinary excretion of carrageenan was limited to low-molecular-weight material (M n ⩽ 20.000). Qualitative and quantitative evidence indicated that there was an upper limit to the size of carrageenan molecules absorbed, but estimates of this upper limit ranged from 10,000 to 85.000 depending upon the analytical approach. Absorption of carrageenan from the drinking-water may differ qualitatively from absorption from the diet. Analysis of faecal samples by gel electrophoresis showed that degradation of high-molecular-weight carrageenan had occurred, either in the gut or in the faeces.