Application of the tan δ method in the determination of the melting temperature of κ-carrageenan gels in the presence of calcium ions

The objective of the present study was to investigate the applicability and suitability of the tan δ method to determine an accurate melting temperature for a 1% (w/w) κ-carrageenan gel in the presence of 20 mM Ca²⁺ during heating. Melting temperature was measured using dynamic oscillatory shear rheometry. Winter and Chambon criterion (tan δ becomes independent of frequency) was used to avoid the frequency dependence on the melting temperature that the conventional temperature sweep rheological method exhibits. The main task was to perform frequency sweeps near the crossover of the storage modulus G′(ω) and loss modulus G"(ω) during heating in a temperature sweep. The crossover point temperature (T_c-o) of G′(ω) and G″(ω) during the temperature sweep procedure in heating occurred at T_c−o = 54.2 ± 1.07 °C. The tan δ method established that T_m,a for 1% κ-carrageenan gel with 20 mM Ca²⁺ system was 55.0 °C. At the melting point, the power-law relaxation exponent n obtained was a constant (n = 0.87 ± 0.01) and independent of temperature. The tan δ method was easy to use and feasible to apply to determine the melting point of a biopolymer-based gel.