Gelation, alginates

Uses. Alginates are used in a wide range of appHcations, particularly in the food, industrial, and pharmaceutical fields (25—27). As shown in Table 5, these appHcations arise from the properties of gelation, thickening/water holding, emulsification, stabilization/binding, and film forming. 

Pectins are generally classed according to their ester content as high methoxyl pectins (>50% of the carboxyl groups esterified) or low methoxyl pectins (<50% of carboxyl groups esterified) (pectic acid, methyl ester [9049-34-1]). Low methoxyl pectins, like algins, require calcium for gelation. 

Fig. 5.5 (A) Alginate block copolymer structure with random sequences (B) divalent cations induced gelation of alginate (formation of egg-box structure).

Wet cells (5g) are suspended in 15 ml of a 1% sodium alginate solution. The mixture is then forced through a syringe needle into a 0.05 M CaCl2-solution containing the necessary nutrients for the cell. Gelation occurs almost immediately. 

Morris, E.R., Rees, D.A., Thom, D., Boyd, J. (1978). Chiroptical and stoichiometric evidence of a specific, primary dimerization process in alginate gelation. Carbohydrate Research, 66, 145-154. 

The principle took advantage of the gelation of alginate at room temperatures in the presence of calcium ions. Recently, a new method was described by Alleyene et al. [16] based on a microcube concept, and compared with older methods. 

Propyleneglycol alginates do not precipitate from acidic media and their acid stability increases in proportion to the propyleneglycol content. Additionally, those esters with DS > 60% are not precipitated by Ca2 +, because the bulky propyleneglycol substituent hinders the prerequisite alignment for gelation and precipitation. These esters are more tolerant of alcohol than the unesterified alginate. 

Toft, K., Grasdalen, H., and Smidsrod, O. (1986). Synergistic gelation of alginates and pectins. In Chemistry and Function of Pectins, ACS Symposium Series 310, pp. 117-132. Am. Chem. Soc., Washington, DC. 

Calcium alginate Gelation None stable in 0.1 N HC1, but not in simulated intestinal fluids ... 

Calcium alginate and poly-L-lysine Gelation Doxorubicin, oligonucleotides [28,89]... 

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