Coil-to-double helix (c-h) and double helix-to-dimer (h-d) phase transitions of ι-carrageenan in CaCl₂ solution upon cooling were studied using photon transmission technique. Photon transmission intensity, I_tr was monitored against temperature to determine the (c-h) and (h-d) transition temperatures (T_ch and T_hd) and activation energies (ΔE_ch and ΔE_hd). An extra dimer-to-dimer (d-d) transition was also observed during cooling at low temperature region. However, upon heating dimers disappear to double helices by making dimer-to-double helix (d-h) transition. Further heating resulted double helix-to-coil (h-c) transition at high temperature region. T_dh and T_ch temperatures and ΔE_dh and ΔE_hc activation energies were also determined. It was observed that T_hc and T_ch temperatures and ΔE_dh and ΔE_hd activation energies do not effected by carrageenan content. However, T_hd, T_dh and T_dd temperatures and ΔE_ch and ΔE_hc activation energies were found to be strongly correlated to the carrageenan content in the system.

Key words: Carrageenan, Phase transition, Activation energy, Transition temperature.