OP-II-3

PP-III-35In the modification process, for polyelectrolytes, counter ions play a major role inthe carrageenan gelation process. Some of the cations are reacted and caused formodification of gelation properties in the natural polymers. Besides, fewinvestigations pertaining to the gelling mechanism, focused on the configuration ofthe initial ordered state of the helices. The gel formation occurred in the presence ofK + , Rb + , Cs + and at high concentrations of Na + and a double helix based‘aggregated-domain’ structure as the gelled structure was proposed [3]. Theaggregation of ‘helical dimers’ to form a three dimensional network in the presence ofpotassium, sodium and rubidium was investigated [4]. At high polymer concentration(~ 21.6 g/l), it was found that the elastic modulus was not affected by divalent saltconcentration above a certain threshold and also proposed that the addition ofcations beyond this critical value contributes only to some localized heterogeneitywithin the gels without affecting the overall viscoelastic properties of the systems [5].The existence of an optimum counter-ion concentration in silver-induced iotacarrageenanfrom ucheuma denticulatum at low polymer concentrations of 1, 1.2 and1.5 weight percent was observed. The weight loss for gels was found to be in therange 0.7-1.2% and after 240 h with a standard deviation of 0.01-0.2%. The gelsexhibited high firmness as the Ag+ concentration increased while decrease in theelasticity was observed. The relaxation time reached maximum at 70 mM of Ag+ andat higher concentration the gels exhibited saturation. Scanning electron microscopeimages show that the extensive structural charge neutralization of the polysaccharideby monovalent silver ions is responsible for a marked aggregation of the polymerstrands reminiscent of precipitation. At lower counter-ion to polymer ratios, the onsetof gelation might prevent such phase separation. Results with higher concentrationssuggested that the iota- carrageenan gel films exhibited cracks on the surface. It wasattributed to the brittleness and lower gel film strength.Reference:[1]. Wu, J., Lin, L., & Foo, T.C., Ultrason. Sonochem. 8 (2001) 347.[2]. Xia, T., Shi, S., & Wan, X., J. Food Eng. 74(2006) 557.[3]. Morris, E. R., Rees, D. A., J. Mol. Biol. 138(1980) 349.[4]. Rochas, C., Rinaudo, Biopolymers, 23(1984) 735.[5]. Michel A-S, M.M.Mestdagh, M.A.V.Axelos., Int. J. Biol. Macromol. 21(1997) 195.505