Rheological investigation of the interaction between amylose and κ-carrageenan

By combining rheological and turbidity measurements, the interaction and viscoelastic properties of amylose–κ-carrageenan mixtures were investigated under conditions allowing gelation of the former and gelation or non-gelation of the latter. Amylose concentration was kept constant (1.34 wt%) and carrageenan content was varied from 0.093 to 1.38 wt%. Amylose was dispersed in water at 150°C and its gelation was induced by quenching aqueous solutions from 80 to 25°C. When desired, carrageenan gelation was also induced by addition of 20 mM KCl. Absorbance and gel-cure profiles were highly dependent on carrageenan concentration and presence of salt. The storage modulus at 15 h depended strongly on carrageenan concentration; for concentrations <0.2%, amylose aggregation occurred rapidly and the rigidity of gels was reinforced as a result of phase separation between amylose and κ-carrageenan. Further addition of carrageenan, either without or with KCl, resulted in a maximum G′ occurring at about 0.2 and 0.3%, respectively. Beyond such values a sharp decrease was observed suggesting phase inversion with carrageenan forming the continuous phase. Above 0.5%, G′ increased steadily showing a predominance of carrageenan gel properties. Results support the existence of at least two different conditions in which amylose and carrageenan form the continuous and disperse phase alternately.