Light scattering studies of irradiated κ- and ι-carrageenan

The relationships between the molecular weight (Mw) and the characteristic decay time distribution function G(Γ) of irradiated kappa (κ-) and iota (ι-) carrageenan were studied by static and dynamic light scattering (DLS). Mw and the characteristic decay time (Γ−1) are both steep decreasing exponential function with radiation dose. The dynamic behavior of irradiated ι-carrageenan was compared to irradiated κ-carrageenan by DLS. The intensity correlation function of both carrageenans shifted towards shorter relaxation times with increasing radiation dose. Irradiated ι-carrageenan like κ-carrageenan exhibits power law behavior at 0-50 kGy (at 0.05-0.1M KCl) indicating similar gelation behaviors. The temperature at which transition from coil to helix takes place (conformational transition temperature) decreases with increasing irradiation dose. A new faster relaxation mode appears at around 0.1-1 ms for both carrageenans between 100 and 150 kGy. Maximum peak height for this mode is at 100 kGy which corresponds to the optimum biological activity of κ- and ι-carrageenan.