Effects of added galacto- and gluco-mannans on the NMR spectra of 133CS ions in kappa-carrageenan gels

Abstract

NMR chemical shifts and line-widths of 133Cs ions were measured in kappa-carrageenan gels containing galacto-or gluco-mannans, and compared with measurements on kappa-carrageenan alone. In the mixed gels, as in pure kappa-carrageenan, large changes in the NMR parameters were found to accompany the onset of helix formation for kappa-carrageenan, as obtained independently from polarimetry or differential scanning calorimetry. The shift changes on helix formation in the mixed gels were very similar to those in kappa-carrageenan alone, indicating that the ordered conformation of kappa-carrageenan, and its degree of specific ion binding, was the same in all systems. A much enhanced line-broadening was seen in gels containing carob galactomannan or konjac glucomannan, which are known to form synergistic gels in the mixtures with kappa- carrageenan, while other additives (guar galactomannan or agarose) had a small or insignificant effect. The observations are interpreted in terms of an association between mannans and (aggregated) kappa-carrageenan helices in the synergistic gel mixtures.