Abstract
Calcium binding, crosslinking, and mechanical properties were studied in alginate gels prepared by a two-step procedure. A thermolabile gelatin gel containing sodium alginate is placed in a calcium lactate solution, and diffusion of calcium ions causes crosslinking of the alginate. Calcium binds completely to alginate within 48 h, but crosslinking continues for more than 72 h, as indicated by gel strength. Retention of ascorbic acid incorporated into these gels was only about 25% after 72 h in the crosslinking bath. To improve retention, an alternate one-step procedure was adopted, using glucono-delta-lactone (GDL) and dicalcium phosphate dihydrate; this process eliminates residence in the crosslinking bath. Hydrolysis of GDL slowly reduces the mixture's pH, releasing calcium ions which then crosslink with the alginate. The GDL process produced a gel matrix with compression behavior similar to those of the “two-step” gels. Complete crosslinking took 7 h; ascorbic acid losses were insignificant.
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