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J. Biol. Macromol., 5(3), 47-52 (2005)
Gelation and gel properties of polysaccharides gellan gum and tamarind xyloglucan
Department of Food and Nutrition, Faculty of Human Life Science, Osaka City Univeristy, 3-3-138, Sumiyoshi-ku, Sugimoto, Osaka City, Osaka, 558-8585, Japan Received September 5, 2005, accepted September 14, 2005 Keywords: Gel, Gelation, texture modifier, gellan, xyloglucan, rheology, DSC Polysaccharide is used widely in food, cosmetic and pharmaceutical industries. The main use is to give appropriate texture to the products. Thus the polysaccharides used in such way are called texture modifier. Here two important texture modifiers, gellan and tamarind xyloglucan are introduced. The former one is a microbial polysaccharide with gelling ability. Gelling ability makes gellan valuable since only a few polysaccharides can form a gel. Most polysaccharides do not form a gel by themselves; however, some can form a gel under appropriate conditions. The latter one is a plant polysaccharide which forms a gel under appropriate conditions. Gelation and gel properties of gellan and tamarind xyloglucan are described. suspension [1]. The polysaccharides used in these ways are called texture modifier and enhance the quality of product by thickening creation of various kinds of texture modifier and gelling, and by reducing the undesired defect of water release (syneresis) in some products, and by stabilizing emulsion and Gelling ability is an important property as a texture modifier and some polysaccharides can form a gel at low concentrations (~1%). There are only a few polysaccharides which have a gelling ability by themselves at low Life and Environment, Nara Women’s University, Kitauoya Nishi Machi, Nara concentration whereas a lot of non-gelling polysaccharides are used as a thickener and calorimetry (DSC), epigallocatechin gallate In the present article, recent insight about the gelation and gel properties of gellan gum and tamarind xyloglucan shall be described. Gellan gum is a polysaccharide 1,4-β-D-glucuronic acid, 1,4-β-D-glucose, which can form a gel at low concentrations. Gelation mechanism and gel properties of O’Neil et al. and Jannson et al. [3, 4]. gellan have not been clarified well at the Gellan gels in the presence of appropriate amount of cations are transparent, resistant polysaccharide obtained from tamarind seed, to heat in the wide range of pH [5]. Brittle is a valuable thickener and stabilizer. We suitable for gel products with new texture. particle, called a microgel, has a specific gelling conditions of tamarind xyloglucan texture like fluid gel which was produced gellan gels, gelation and gel properties have fundamental questions still remain to be polysaccharide produced by micro-organism previously known as Pseudomonas elodea. properties of gellan gum, a collaborative research group was organized conjunction quality. The primary structure of gellan gum is composed of a linear tetrasaccharide affiliated to the Society of Polymer Science, Fig. 1. (a) The storage Young’s modulus and (b) the circular dichroism spectra of 1 wt % K-gellan gels affected by the immersion in NaCl solutions or distilled water. used to study its properties with various dramatically under gel state at a certain techniques. The results of the collaborative studies were published in special issues of Food Hydrocolloids 7, 361-456 in 1993, differential scanning calorimetry (DSC) and Carbohydrate Polymers 20, 75-207 in 1996, and Progress in Colloid and Polymer Science, 114, 1-131 in 1999. Light helix-coil transition of gellan; thus, we concluded that a helix-coil transition can from two single chains to one double helix occur even in gel state. Since gellan is a polyelectrolyte, gel properties are influenced helix to two single chains on heating [7, 8]. gel formation occurs after the coil-to-helix modulus of the gel increased and circular dichroism spectra changed as shown in Fig.1. This was also attributed to the helix-coil gelation mechanism is described in those Gel properties also remain to be clarified. We found that rheological properties change Fig. 2. The appearance of 1 wt % tamarind xyloglucan in the presence of epigallocatechin gallate (EGCG). polysaccharide in the primary cell walls of two-dimensional nuclear Overhauser effect obtained from the endosperm of the seed of the tamarind tree, Tamarindus indica, a member of the evergreen family, that is one mixtures of polysaccharides can form a gel of the most important and common trees of India, Bangladesh, Myanmar, Sri Lanka, and prepared in order to test whether or not the Malaysia [11]. Purified, refined tamarind mixture shows a specific interaction leading to a synergistic gelation. From viscoelastic permitted as a thickening, stabilizing, and mixture formed a gel under the condition where individual polysaccharide does not (1→4)-β-D-glucan backbone that is partially concentrations, indicating the synergistic measurements, the gelation was detected as xylose residues are β-D-galactosylated at a peak that appeared at higher temperatures than a peak arising from helix-coil transition Although tamarind xyloglucan itself does of gellan alone [17]. It was also detected not form a gel, gel can be obtained under as a change in circular dichroism which was appropriate conditions, such as by adding not observed in tamarind xyloglucan alone some substances or removing substituents. xyloglucan and gellan might associate to galactose residues from tamarind xyloglucan [14, 15]. In order to seek novel gelling Recent findings about gellan and tamarind xyloglucan are the helix-coil transition of prepared a mixture of tamarind xyloglucan gellan in gels, the gelation of tamarind xyloglucan by addition of epigallocatechin gallate, and the synergistic gelation of a mixture formed a translucent or opaque gel mixture of tamarind xyloglucan and gellan. (Fig.2) [16]. Rheological and DSC studies It should be noted that it is rare for the showed that the gelation occurred on cooling and gel melted on subsequent heating [16]. leading to gel formation. It is also notable that only a few mixtures of polysaccharides xyloglucan chains for a gel network, which findings are expected to contribute to not polysaccharides but also create new texture modifiers suitable for social requirement. in aqueous solutions. Prog. Colloid Polym. Sci., 114, 8-14.
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