Viscometric studies on xanthan and galactomannan systems

Dietary roles of non-starch polysaccharides in human nutrition: a review

Nonstarch polysaccharides (NSPs) occur naturally in many foods. The physiochemical and biological properties of these compounds correspond to dietary fiber. Nonstarch polysaccharides show various physiological effects in the small and large intestine and therefore have important health implications for humans. The remarkable properties of dietary NSPs are water dispersibility, viscosity effect, bulk, and fermentibility into short chain fatty acids (SCFAs). These features may lead to diminished risk of serious diet related diseases which are major problems in Western countries and are emerging in developing countries with greater affluence. These conditions include coronary heart disease, colo-rectal cancer, inflammatory bowel disease, breast cancer, tumor formation, mineral related abnormalities, and disordered laxation. Insoluble NSPs (cellulose and hemicellulose) are effective laxatives whereas soluble NSPs (especially mixed-link β-glucans) lower plasma cholesterol levels and help to normalize blood glucose and insulin levels, making these kinds of polysaccharides a part of dietary plans to treat cardiovascular diseases and Type 2 diabetes. Moreover, a major proportion of dietary NSPs escapes the small intestine nearly intact, and is fermented into SCFAs by commensal microflora present in the colon and cecum and promotes normal laxation. Short chain fatty acids have a number of health promoting effects and are particularly effective in promoting large bowel function. Certain NSPs through their fermented products may promote the growth of specific beneficial colonic bacteria which offer a prebiotic effect. Various modes of action of NSPs as therapeutic agent have been proposed in the present review. In addition, NSPs based films and coatings for packaging and wrapping are of commercial interest because they are compatible with several types of food products. However, much of the physiological and nutritional impact of NSPs and the mechanism involved is not fully understood and even the recommendation on the dose of different dietary NSPs intake among different age groups needs to be studied.

An overview of mannan structure and mannan-degrading enzyme systems

Hemicellulose is a complex group of heterogeneous polymers and represents one of the major sources of renewable organic matter. Mannan is one of the major constituent groups of hemicellulose in the wall of higher plants. It comprises linear or branched polymers derived from sugars such as D-mannose, D-galactose, and D-glucose. The principal component of softwood hemicellulose is glucomannan. Structural studies revealed that the galactosyl side chain hydrogen interacts to the mannan backbone intramolecularly and provides structural stability. Differences in the distribution of D-galactosyl units along the mannan structure are found in galactomannans from different sources. Acetyl groups were identified and distributed irregularly in glucomannan. Some of the mannosyl units of galactoglucomannan are partially substituted by O-acetyl groups. Some unusual structures are found in the mannan family from seaweed, showing a complex system of sulfated structure. Endohydrolases and exohydrolases are involved in the breakdown of the mannan backbone to oligosaccharides or fermentable sugars. The main-chain mannan-degrading enzymes include beta-mannanase, beta-glucosidase, and beta-mannosidase. Additional enzymes such as acetyl mannan esterase and alpha-galactosidase are required to remove side-chain substituents that are attached at various points on mannan, creating more sites for subsequent enzymatic hydrolysis. Mannan-degrading enzymes have found applications in the pharmaceutical, food, feed, and pulp and paper industries. This review reports the structure of mannans and some biochemical properties and applications of mannan-degrading enzymes.

Characterization of polysaccharide hydrogels for modified drug delivery

Hydrogels are hydrophilic macromolecular networks that are capable of retaining a large amount of water. A precise description of these systems is actually quite complex and the practical use of hydrogels for drug delivery and biomedical applications is often not supported by a well-defined knowledge of the overall structure of the polymeric network. In this paper, we report the characterization of two different systems: a chemical network based on Guar Gum (GG) and a physical gel prepared with Xanthan (Xanth) and Locust Bean Gum (LBG). The dynamo-mechanical properties of the gels were analysed: the cohesiveness and the adhesion of the networks were strongly dependent on time, temperature, and composition. The kinetics of the chemical crosslinking was followed by means of rheological measurements, i.e. recording the mechanical spectra of the gelling system, and the power law exponent at the gel point was evaluated. Furthermore, the networks, loaded with model drugs with different steric hindrance, were used as matrices for tablets and the rate of release of such model drugs was studied. The diffusion of the guest molecules was deeply dependent on their dimensions; in the case of Xanth-LBG tablets the release profiles were almost independent from the different cohesion properties of the starting hydrogel composition.

Rheological Study of Binary Gels with Carbopol UltrezTM 10 and Hyaluronic Acid

The objective of this study is to provide a rheological characterization of binary hydroalcoholic gels made with Carbopol Ultrez 10 (U10) and Hyaluronic Acid (HA) as a function of polymer concentration: U10 (0.0-2.0% w/w) and HA (0.00-0.20% w/w), and to determine the influence of this combination on the thixotropic properties of the resulting binary systems. Interaction of the two polymers was measured using the Viscose Synergy Index (I(S)) and thixotropic analysis, which indicate the structural changes that take place in binary gels attributable to molecular interactions between the gelling agents. The maximum values for viscose synergy (I(S)=1.22-1.44) are obtained for the U10 : HA mixtures with a polymer proportion of 10 : 1. The behavior of the binary gels studied is the result of the formation of a more structured three-dimensional network between the U10 and HA molecules. Shearing of this polymer network requires application of a greater force than is needed to shear the structure of the separate gels. Inclusion of HA in a proportion of 1 : 10 has a fixing effect on the polymer network, resulting in greater resistance to shearing in the compound gel. The relative thixotropic area -A(R)- shows maximum values (A(R)=17.215%) for the same polymer composition. The evolution of the two parameters indicates that restructuring of the molecular interactions for this polymer proportion (10 : 1) takes place; the result is a reinforced three-dimensional structure in the gelled system, which increases the thixotropic properties. The same composition leads to a maximum of thixotropic properties as well as viscose synergy because both characteristics are closely related to structural changes observed in the binary systems of this composition. Thixotropic systems have a very wide area of application in the pharmaceutical industry. For this reason, the results obtained here considerably increase the use of the gels studied. In fact, incorporation of HA significantly improves a property of acrylic gels which has direct repercussions on the ease and efficiency of their application to the skin.

Role of Substituents on the Properties of Some Polysaccharides

This paper concerns the influence of the chemical structure on the physical properties of some polysaccharides. Especially, we proposed to discuss the role of the substituents on these properties. In some cases, non-carbohydrate substituents play a minor role on rheological properties in the presence of a salt excess as shown on xanthan and succinoglycan. The rheology of aqueous solution of these stereoregular polysaccharides is controlled by the conformation (helical conformation) whose stability is not largely influenced by these substituents. On the other hand, the interaction between galactomannan and xanthan depends on the presence of acetyl substituents on xanthan but also on the xanthan conformation. However, for polymers such as gellan, XM-6 or BEC 1615, complete deacetylation induces the ability to form physical gels in given thermodynamic conditions. The presence of carbohydrate substituents or short side chains was also examined. Especially in the gellan family, the role of position of substitution (position 3 on the glucose unit C or position 6 on the A glucose) was presented. It is concluded that the substituents giving the higher stability for the helical conformation (higher DeltaH and Tm values) also cause a lower salt sensitivity for the helical stability. The role of the substituents on the properties is also described for natural polymers and their chemically or enzymatically modified derivatives.

Evaluation of xanthan and highly substituted galactomannan from M. scabrella as a sustained release matrix

A highly substituted galactomannan (G) from Mimosa scabrella Bentham (Man:Gal 1.1:1), isolated from the seeds of a Brazilian leguminous tree and xanthan (X), an exopolysaccharide secreted by Xanthomonas campestris (Keltrol), were evaluated as a hydrophilic matrix system (XG) for controlled release (CR) of diclofenac sodium (DS) in tablets and capsules. The performance of XG (2:1) matrices containing 50 mg (A) or 100 mg (B) of DS was compared with a commercial CR product of DS. The drug release studies were carried out using a dissolution apparatus (paddle method) with gradual increase of pH values, from pH 1.4, to pH 4.0 (after 1 h) and to pH 6.8 (after 2 h). The results suggested the potential of XG systems as release retarding materials, which released 78.6 and 35.1% of drug after 24 h for capsules (A) and tablets (A), respectively. Drug release decreased with the increase of amount of drug and it is dependent of dosage form. Analysis of release data indicate a rather zero-order drug release with the erosion mechanism playing a dominant role.

Development of a cream from a self-emulsifying base and moisturizing actives

This research study is based on the design and development of a semisolid emulsion system whose novel self-emulsifying base and preferentially moisturizing actives were investigated to find out whether the system mentioned could be used as a dermatological treatment for highly sensitive skins, including atopic ones. Thus, one of the main objectives of the present study consisted of in vivo evaluation of its effectiveness by means of non-invasive assessment techniques currently employed in cosmetology. Due to the fact that the new formula is, in principle, designed for skins that could present any kind of alteration, the current study was focused on rheological parameters of viscosity, thixotropy, and extensibility to guarantee not only an accurate assessment of composition but also a comfortable and safe application on skin.

Role of galactomannan composition on the binary gel formation with xanthan

The influence of the galactomannan characteristic ratios (M/G) on the temperature of gelation (Tg) and the gel strength of mixtures of galactomannan with xanthan is reported. Two galactomannans were investigated: one highly substituted from the seeds of Mimosa scabrella (M/G = 11), and the other, less substituted, from the endosperm of Schizolobium parahybae, with (M/G = 30) [Ganter JLMS, Zawadzki-Baggio SF, Leitner SC, Sierakowski MR, Reicher F. J Carbohydr Chem 1993;12:753]. The xanthan:galactomannan systems (4:2 g l(-1), in 5 mM NaCl) showed a temperature of gel formation (Tg) of 24 degrees C for that of S. parahybae [Bresolin TMB, Milas M, Rinaudo M and Ganter JLMS. Int J Biol Macromol 1998;23:263] and 20 degrees C for the galactomannan of M. scabrella, determined by viscoelastic measurements and microcalorimetry. A Tg of 40-50 degrees C was found by Shatwell et al. [Shatwell KP, Sutherland IW, Ross-Murphy SB, Dea ICM. Carbohydr Polym 1991;14:29] for locust bean gum-LBG (M/G = 43). Lundin and Hermansson [Lundin L, Hermansson AM. Carbohydr Polym 1995;26:129] reported a difference of 13 degrees C for Tg of two LBG samples with M/G = 3 (40 degrees C) and 5 (53 degrees C), in mixtures with xanthan. It appears that the more substituted galactomannans have lower temperatures of gelation in the presence of xanthan. The mechanism of gelation depends also on the M/G ratio. For the lower values it involves only disordered xanthan chains in contrast to M/G ratios higher than 3. In addition, the presence of the galactomannan from M. scabrella increased slightly the temperature of the conformational change (Tm) of xanthan probably due to the ionic strength contribution of proteins (3.9%) present in the galactomannan. On the other hand, the galactomannans from S. parahybae, with 1.5% of proteins and M. scabrella, with 2.4% of protein, did not show this effect, the Tm of xanthan alone or in a mixture being practically unchanged.

Xanthan-galactomannan interactions as related to xanthan conformations

The influence of xanthan conformation on the physicochemical behaviour of their mixtures with galactomannan from Schizolobium parahybae mannose:galactose ratio (M/G=3), was studied by viscoelastic measurements, differential scanning calorimetry (DSC) and chiroptical (circular dichroism) methods. The results suggested a more effective interaction of the galactomannan with disordered xanthan segments, which are more abundant in low salt concentrations but are still present in lower proportion at temperatures lower than the temperature of xanthan conformational transition (Tm). The dependence of ellipticity with temperature in a circular dichroism (CD) spectra suggested an ordering of the xanthan chains induced by galactomannan at the temperature of gel formation (Tg approximately 25 degrees C), under conditions where xanthan alone exhibits a disordered conformation. The lower Tg value found (approximately 25 degrees C) compared with that (60 degrees C) usually described in the literature is certainly related to the M/G ratio and the galactosyl unit distribution along the mannan main chain.