Polysaccharide gels curdlan

C3K produces an insoluble exocellular polysaccharide(1). This polysaccharide is entirely composed of D-glucosyl residues which are connected almost exclusively by B-(l- -3)-linkages. This and the similar glucan formed by some strains of Agrobaoterium are named Curdlan because they form irreversibly, resilient gel when heated in water. 

Harada, T., Kanzawa, Y., Kanenaga, K., Koreeda, A., and Harada, A. (1991). Electron microscopic studies on the ultrastructure of curdlan and other polysaccharides in gels used in foods. Food Struct. 10 1. 

Nakanishi, I., Kimura, K., Kusui, S., and Yamazaki, E. (1974). Complex formation of gel-forming bacterial (l,3)-P-D-glucans (curdlan-type polysaccharides) with dyes in aqueous solution. Carbohydr. Res. 32 47-52. 

Curdlan gel formation is heat dependent. This polysaccharide is not soluble in water, but when an aqueous suspension is heated it becomes dear at about 54°C. Furdier heating leads to gel fonnation. The gels are stable over a wide range of pH (3 to 95) and do not melt at temperatures below 100°C. Curdlan gels are formed by cross-linldng, involvii conformational ordering of the exopolysaccharide molecules to give a triple helical structure. 

Curdlan is a bacterial polysaccharide made by Agrobacterium biovar [87,88,89]. It is a linear (1 3)- -glucan (MW 73,000) that forms a triple helix. Curdlan is insoluble in cold water. When aqueous dispersions of curdlan are heated, two types of gels form. First curdlan dissolves. When the solution reaches 55-66 °C, then is cooled, a reversible gel forms. The gel melts when held at about 60 °C. When the thermoreversible gel is heated to a temperature above 80 °C, an irreversible gel forms. Heating to higher temperatures results in stronger irreversible gels. Transition temperatures are a function of concentration. 

Gels of curdlan can also be prepared by neutralizing an aqueous NaOH solution of this polysaccharide. For the system we have studied, a 0.5 M NaOH solution containing 5% curdlan was subjected to dialysis against water to yield a gel. Under these conditions curdlan would be present as random-coil rather than triplex structure before gelation. A CP/MAS NMR... 

The melting points and heats of junction formation of curdlan gels depend on the concentration and DP of the polysaccharide [a (1 3)-P-D-glucan from Alcaligenes faecalis. The junction zones of the gels appear to form in regions of aggregation of intertwined helices. X-Ray diffraction studies have revealed that curdlan assumes a triple-helical structure. ... 

X-Ray diffraction studies on the (l->3)-j8-D-gIucan, curdlan, from Alcaligenes faecalls have shown the existence of microfibril formation, and a triple helical structure is proposed for the crystalline form of this polysaccharide. The effects of applied hydrostatic pressure on the gel structures of the polysaccharide have been reported. The elasticity decreases initially with increasing pressure attributed to a decrease of free water as solvent, but then increases as the pressure is increased due to the promotion of hydrogen bonding by compression. 

Saito H., Ohki X, and Sasaki X. 1977. A C nuclear magnetic resonance study of gel forming (1 3)-P-D-glucans. Evidence of the presence of single-helical conformation in a resilient gel of a curdlan-type polysaccharide 13140 from Alcaligenes faecalis var. myxogenes IFD 13140. Biochemistry 16 908-914. 

Agarose gel, which exhibits elasticity similar to that of Curdlan, clearly provides signals from the solution-like region as shown in the upper C DD-MAS spectrum of Fig. 6 [130]. However, a spectrum similar to this can also be obtained by the CP-MAS technique as shown in the bottom spectrum of Fig. 6 (the solid-like region). However, there appears to be a difference in the 77-78.5 ppm resonance, which is the characteristic region of polysaccharide chains. Unlike in the solid-like region, this difference is thought to arise from the random coil structure in... 

Curdlan is a microbial polysaccharide that occurs naturally as a linear (triple-helix) polysaccharide composed of 1,3-P-hnked D-glucose units, produced by a strain of Mcaligenes faecalis (Figure 2.38). It is a neutral, bacterial polysaccharide without branched chains. It is insoluble in water and alcohol but soluble in alkaline solution and dimethyl sulfoxide (DMSO) [274-276]. It occurs as a tasteless powder, stable in dry state. It was reported as a support matrix for enzyme immobilization, through activation with epichlorohydrin that can be covalently linked to the available amino, hydroxyl, and suHhydryl enzyme groups [277]. It has the specific character to form an irreversible gel by heating of a water suspension [278]. Its water-insoluble nature helps to improve a material s water barrier capabihty, and its solubility in... 

---