Thermal stability and transition temperatures of monovalent salts of high-acyl gellan gels

Thermogravimetry/derivative thermogravimetry (TG/DTG), rheometry and differential scanning calorimetry (DSC) were used to study the thermal stability and determine the transition temperatures of the sodium and potassium salts of high-acyl gellan (HAG) in the presence of 0-100mm NaCl and KCl, respectively. TG/DTG revealed the potassium gellan (KHAG) gels to be more stable than those of sodium gellan (NaHAG), regardless of external cation concentration. Rheometry and DSC showed the melting (T-m) and gelling (T-g) temperatures to increase with cation concentration. The DSC peak temperatures showed thermal hysteresis contrary to rheometry. In most cases, DSC revealed KHAG to exhibit higher T-m and T-g than NaHAG. Consequently, thermal characteristics of NaHAG and KHAG gels depend on the size of the external cation and its ability to coordinate water molecules. Cation salts of HAG exhibit significantly lower transition temperatures than the commercial preparation from which they were produced.