Molecular characterisation of kappa- and lambda-carrageenan by gel permeation chromatography, light scattering, sedimentation analysis and osmometry

Preparation, Properties and Potential of Carrageenan-Based Hard Capsules for Replacing Gelatine: A Review

Intense efforts to develop alternative materials for gelatine as a drug-delivery system are progressing at a high rate. Some of the materials developed are hard capsules made from alginate, carrageenan, hypromellose and cellulose. However, there are still some disadvantages that must be minimised or eliminated for future use in drug-delivery systems. This review attempts to review the preparation and potential of seaweed-based, specifically carrageenan, hard capsules, summarise their properties and highlight their potential as an optional main component of hard capsules in a drug-delivery system. The characterisation methods reviewed were dimensional analysis, water and ash content, microbial activity, viscosity analysis, mechanical analysis, scanning electron microscopy, swelling degree analysis, gel permeation chromatography, Fourier-transform infrared spectroscopy and thermal analysis. The release kinetics of the capsule is highlighted as well. This review is expected to provide insights for new researchers developing innovative products from carrageenan-based hard capsules, which will support the development goals of the industry.

An analytical ultracentrifugation based study on the conformation of lambda carrageenan in aqueous solution

The conformation and heterogeneity of lambda-carrageenan, a sulphonated galactan from red seaweed, solubilised in aqueous solvent with the assistance of microwave irradiation, has been assessed by a combination of analytical ultracentrifugation, size-exclusion chromatography, light scattering and capillary viscometry. Preparations appeared generally unimodal on the basis of sedimentation coefficient distributions from sedimentation velocity although at the highest concentrations a shoulder appears with a sedimentation coefficient approximately 1.1 times greater than that of the main component. Even under conditions commensurate with charge suppression simple linear regression was insufficient to represent non-ideal concentration dependence and the extraction of the Grálen concentration dependence parameter ks. A more general fitting algorithm was therefore employed. Mark-Houwink-Kuhn-Sakurada analysis of the change in intrinsic viscosity [η] with molecular weight, together with the Wales-van Holde ratio (combination of ks with [η]) point to an extended flexible conformation for lambda-carrageenan in the (weight average) molecular weight range Mw=340,000-870,000g/mol. The origin of the larger sedimentation coefficient component appearing at the higher concentrations is considered.

Rheological behavior and non-enzymatic degradation of a sulfated galactan from Halymenia durvillei (Halymeniales, Rhodophyta)

The rheological behavior of a sulfated galactan extracted from Halymenia durvillei, a red seaweed collected in the coastal waters of a small island of Madagascar (Nosy-be in Indian Ocean), was investigated in dilute and semi-dilute solutions. In dilute solution with NaCl at 0.3 M, the polysaccharide adopted a coil conformation whereas, at higher concentrations, the polymer had the behavior of shear-thinning fluid, typical of polymer with high molar mass or semi-rigid conformation. Degradations of this lambda carrageenan-like, using radical depolymerization, and high-pressure homogenization led to several samples of various and controlled molar masses. The measure of their intrinsic viscosities permitted the determination of the relationship of Mark-Houwink-Sakurada.

Polysaccharides of the red algae

Red algae (Rhodophyta) are known as the source of unique sulfated galactans, such as agar, agarose, and carrageenans. The wide practical uses of these polysaccharides are based on their ability to form strong gels in aqueous solutions. Gelling polysaccharides usually have molecules built up of repeating disaccharide units with a regular distribution of sulfate groups, but most of the red algal species contain more complex galactans devoid of gelling ability because of various deviations from the regular structure. Moreover, several red algae may contain sulfated mannans or neutral xylans instead of sulfated galactans as the main structural polysaccharides. This chapter is devoted to a description of the structural diversity of polysaccharides found in the red algae, with special emphasis on the methods of structural analysis of sulfated galactans. In addition to the structural information, some data on the possible use of red algal polysaccharides as biologically active polymers or as taxonomic markers are briefly discussed.

Thermoreversible gelation of kappa-carrageenan: relation between conformational transition and aggregation

We have studied, by optical rotation dispersion, light scattering and rheology, the kappa-Carrageenan system to elucidate the processes involved in gel formation (on decreasing the temperature) and gel melting (on increasing the temperature). Our results show that, on decreasing the temperature, a conformational transition from coils to double helices first occurs, followed by aggregation of the double helices into domains and gel formation at appropriate polymer concentration. Structural details of this sequence are better revealed by re-heating the system. Melting appears as a two-step process characterized by first a conformational change of helices involved in junction zones between aggregates, followed by the conformational transition of the helices inside the aggregates. These helices can regain the coil conformation only when the aggregates melt at higher temperature, in full agreement with the old 'domain' model. The full description of the sol-gel mechanism of this system can be useful in the search for new methods to control the gel texture, a relevant property for many industrial applications.

On-line direct determination of the second virial coefficient of a natural polysaccharide using size-exclusion chromatography and multi-angle laser light scattering

By combining a size-exclusion chromatographic (SEC) separation and an on-line multi-angle light scattering (MALLS) analysis, we have elaborated an original methodology permitting on-line direct determination of the second virial coefficient of molar mass fractions of polydisperse polysaccharides. By assimilating the SEC-MALLS data to a batch mode acquisition, we have obtained on-line the complete Zimm plot of the eluted fractions, leading to knowledge of their weight-average molar mass Mw, radius of gyration r(g) and second virial coefficient A2. Our methodology was successfully applied to a iota carrageenan sample in LiCl 100 mM, EDTA 1 g/l.

Molecular weight distribution of carrageenans studied by a combined gel permeation/inductively coupled plasma (GPC/ICP) method

Degraded carrageenan (known as poligeenan molecular weight: 20 kDa to 30 kDa) causes ulcerative colitis in experimental animals. In this paper, the molecular weight distributions of 29 samples of food-grade refined carrageenans were studied by high performance liquid gel permeation chromatography (GPC) directly connected to vacuum-ultraviolet inductively coupled plasma-atomic emission spectrometry (ICP) (GPC/ICP) as well as GPC/refractive index (RI) detection. All samples of food-grade carrageenan had a major broad peak of high molecular weight which eluted at around 6.5 min in both RI and ICP mode (sulphur and carbon), and each sample of them had no obvious peak of poligeenan (the detection limit was about 5%). The number average molecular weights of these carrageenans ranged from 193 kDa to 324 kDa, and the weight average molecular weights ranged from 453 kDa to 652 kDa based on RI data. Some samples had a few minor peaks which eluted around 10-12 min. These peaks came from ionic sulphate, sucrose or glucose. It was considered that if the data-sampling programme was improved, the GPC/ICP system would become a more powerful technique for evaluation of carrageenan samples containing ionic substances and sugar.

Influence of ionic effects on the ordering and association phenomena in dilute and semidilute carrageenan solutions

A small angle X-ray scattering (SAXS) study was made on Na(+)-kappa- and Na(+)- or Li(+)-iota-carrageenan in aqueous solutions with and without added salt in the dilute (approximately 6 mg/ml) and semidilute (approximately 16 mg/ml) regime close to the critical concentration (approximately 9-11 mg/ml). This concentration should be understood to be determined by contacts between blobs rather than between isolated molecules. The SAXS data of carrageenan solutions are described in terms of the fluctuation model of Borue-Erukhimovich rather than by a particle-type model, although the latter form of scattering appears when aggregates of ordered fragments are formed. According to current models of carrageenan the ordered fragments are single or double chain helices. In conditions favorable for the appearance of the ordered conformation, two polymer subsystems with a different characteristic screening scale of Coulombic interaction for the ideal Gaussian chain are detected. The system with the larger characteristic screening scale corresponds to molecular fragments with an ordered conformation. The contribution of both systems to the scattering can be separated which allows for discussion of their behaviour in the framework of the fluctuation theory. The SAXS results suggest that in all dilute and in the semidilute solutions with added NaCl or LiCl for both kappa- and iota-carrageenans there is a transformation from short-length correlated (disordered) to longer-length correlated (ordered) molecular fragments followed by the association of the ordered fragments, whereas a transformation from an association of disordered fragments to a structure with ordered fragments is detected in semidilute solutions of Li(+)-iota-carrageenan in Li(+)-iota-carrageenan in LiI and Na(+)-kappa-carrageenan in NaI. In the semidilute solutions of Na(+)-iota-carrageenan in NaI the formation of ordered fragments seems to follow an intermediate sequence.

Small-angle X-ray scattering of kappa- and iota-carrageenan in aqueous and in salt solutions

Aqueous and saline (0.03-0.08 M NaCl) solutions of the Na(+)-salt of kappa- and iota-carrageenan (3-17 mg/ml) have been investigated using small-angle X-ray scattering (SAXS). Investigation of the SAXS curves normalized for concentration allows to detect the transition from the dilute to the semidilute regime. Some of the experimental curves exhibit a clear maximum. In the case of kappa-carrageenan, the position of this maximum is proportional to the cube root of polysaccharide concentration. The fluctuation theory of Borue and Erukhimovich (BE theory), which predicts a maximum in the scattering curves for low ionic strength, gives a good fit for all our experiments. An increase of the polymer concentration or the ionic strength causes the appearance of two subsystems in solution exhibiting a different characteristic screening scale of Coulombic interaction for ideal Gaussian chains (and two different segment lengths). The condition for an increase of the relative contribution of the subsystem with the larger segment length correlates with the one for the disorder-order transition of carrageenan. In the most concentrated (17.1 mg/ml) solution of Na(+)-iota-carrageenan, the increase of NaCl molarity above 0.06 M gives rise to additional scattered intensity at the smallest angles, indicating molecular association.