Antifreeze activities of poly(γ-glutamic acid) produced by Bacillus licheniformis

Various enantiomeric isomers, metals salts and molecular sizes of poly(γ-glutamic acid), γ-PGA, produced by Bacillus licheniformis CCRC 12826, were prepared and their antifreeze activities were studied by differential scanning calorimetry. The antifreeze activity of γ-PGA increased as its molecular weight decreased but was indifferent to its d/l-glutamate composition. The antifreeze activity was cation dependent decreasing in the order Mg2+>>Ca2+∼Na+>>K+ which follows that of inorganic chlorides in that high ionic charge leads to high antifreeze activity. The mechanism by which the cryoprotective effects of γ-PGA can be explained is still yet to be determined.