Ionic and acid gel formation of epimerised alginates; the effect of AlgE4

AlgE4 is a mannuronan C5 epimerase converting homopolymeric sequences of ma nnuronate residues in alginates into mannuronate/guluronate alternating seq uences. Treating alginates of different biological origin with AlgE4 result ed in different amounts of alternating sequences. Both ionically cross-link ed alginate gels as well as alginic acid gels were prepared from the epimer ised alginates. Gelling kinetics and gel equilibrium properties were record ed and compared to results obtained with the original non-epimerised algina tes. An observed reduced elasticity of the alginic acid gels following epim erisation by AlgE4 seems to be explained by the generally increased acid so lubility of the alternating sequences. Ionically (Ca2+) cross-linked gels m ade from epimerised alginates expressed a higher degree of syneresis compar ed to the native samples. An increase in the modulus of elasticity was obse rved in calcium saturated (diffusion set) gels whereas calcium limited, int ernally set alginate gels showed no change in elasticity. An increase in th e sol-gel transitional rate of gels made from epimerised alginates was also observed. These results suggest an increased possibility of creating new j unction zones in the epimerised alginate gel due to the increased mobility in the alginate chain segments caused by the less extended alternating sequ ences. (C) 2000 Elsevier Science B.V. All rights reserved.