Effects of alkali metal salts on the viscoelasticity of funoran and λ-carrageenan

Abstract

This chapter describes the experiments conducted to gain an insight on the effects of alkali metal salts on the viscoelasticity of Funoran and λ-Carrageenan. Dynamic viscoelastic measurements and differential scanning calorimetry (DSC) were carried out for the aqueous solutions of λ -carragpenan and funoran with and without alkali metal salts. DSC endothermic peak temperature of 2wt% λ -carrageenan solution remarkably shifted to higher temperatures by the addition of alkali metal salts with comparison to that in funoran solution. Both storage and loss shear moduli G' and G" of 2wt% solutions of λ-carrageenan and funoran were strongly frequency dependent at 25°C, typical of a behavior of dilute polymer solutions. The addition of alkali metal salts increased G' and made G' less frequency dependent. This tendency was more conspicuous in λ-carrageenan than in funoran. The difference in the effect of alkali metal salts is attributed to the different modes of linkage of sulfate groups—a sulfate group is axially linked to C6 in λ -carrageenan, whilst it is equatorially linked to C6 in funoran.Both carrageenan and funoran are polysaccharides extracted from red seaweeds. Carragpenans are extracted from Eucheuma cottonii, and consist of D-galactose, 3,6-anhydro-D-g9lactose, and sulfte esters, and have been used widely in dairy products, sausages and hams because (l) they react with protein, (2)their gelling ability increases remarkably by the addition of monovalent or divalent cations, (3)they interact synergistically with locust bean gum.