PURIFICATION OF COMMERCIAL GELLAN TO MONOVALENT CATION SALTS RESULTS IN ACUTE MODIFICATION OF SOLUTION AND GEL-FORMING PROPERTIES

Lithium, sodium, potassium, and ammonium salts of the industrial polys accharide gellan were prepared. The salts were freely soluble in water at room temperature (25 degrees C). The opinion had been generally he ld that heating to 100 degrees C was necessary for gellan to achieve c omplete solubility in the presence of mono- or multivalent cations. Th en, upon cooling, the solutions would form gels. These conclusions wer e based on the properties imposed upon gellan samples by the presence of contaminating divalent cations. Commercial gellan samples contain c alcium and magnesium at levels exceeding 0.9%, sufficient for counteri on formation with over one-third of gellan's carboxyl groups. Purifica tion was rapid and included sequential treatments with a cation-exchan ge (H+) resin, LiOH, NaOH, KOH, or NH4OH, and an anion-exchange (Cl-) resin. About 95% of the divalent cations and nearly 90% of the phospha te that contaminated commercial gellan were removed. The purified mono valent salts of gellan set in the presence of divalent cations and pro vide well-defined agents for gelling media used for propagation of mic robes and plants. In a manner analogous to sodium alginate, solutions of lithium, sodium, potassium, or ammonium gellanate form beads when d ropped into solutions of divalent cations. This property was exploited for entrapment of enzymes and cells in beads.