Comparative studies on the conformational change and aggregation behavior of irradiated carrageenans and agar by dynamic light scattering

The conformational associative properties of κ-, ι-, and λ-carrageenan and agar with irradiation dose were studied by dynamic light scattering. The random scission of the carrageenans and agar by gamma irradiation resulted in the formation of polydispersed lower molecular weight fragments. At high doses, the system moves towards uniformity. Conformational change from coil to helix was observed in all carrageenans and agar at doses up to 100 kGy. The conformational change in λ-carrageenan may be due to the irregular and hybrid structure of this polysaccharide. Only agar and λ-carrageenan still undergo conformational transition at a high dose of 200 kGy. Gelation is observed for κ-, ι-carrageenan up to a dose of 50 kGy while gelation is still observed at 100 kGy for agar. Increase in the hydrodynamic radius with decreasing temperatures for the non-irradiated carrageenans follows this order: λ-carrageenan > κ-carrageenan > ι-carrageenan. Slight increases in hydrodynamic radius were observed with irradiation.