Thermal degradation and rheological properties of different hydrocolloid gums

The thermal degradation and rheological behavior of hydrocolloid gums are strongly influenced by their molecular architecture, but these properties are rarely evaluated together to establish structure–property relationships. This study comparatively investigated xanthan, guar, fenugreek, and Arabic gums using thermogravimetric analysis (TGA), Flynn–Wall–Ozawa (FWO) and Kissinger kinetic models, initial polymer decomposition temperature (IPDT), thermal heat resistance index (THRI), and oscillatory rheology. The study calculated the activation energy of these four gums using two different methods. The activation energies (Ea) calculated using the Kissinger method for the four gums (xanthan, guar, fenugreek, Arabic) are 168.6, 145.6, 104.7, and 157.1 kJ mol−1, respectively; the values calculated using the FWO method are 194.96, 151.88, 152.56, and 150.23 kJ mol−1, respectively. The FWO activation energy value of xanthan gum is higher than that of all other gums, but the reliability of this value is far less stable (R2 = 0.89) than its Kissinger value (R2 = 0.99). Therefore, one must be especially cautious when interpreting this value, and must not directly compare it randomly with the values of other gums. The Arabic gum has the highest heat resistance index among the four gums, but its initial decomposition temperature; that is, the temperature at which the gum just begins to undergo thermal decomposition is the lowest among the four. This shows that these two indicators reflect completely different dimensions of stability, and one cannot simply use a single indicator to judge which gum has better thermal stability. In terms of rheological properties, the study also measured two core indicators: one is the storage modulus G′, which can be simply understood as the ability of the gum to store elasticity, and the other is the loss modulus G″, which represents the gum’s ability to dissipate energy and exhibit viscosity. The measured order of storage modulus is xanthan gum > guar gum > fenugreek gum > gum Arabic, while the order of loss modulus is guar gum > xanthan gum > fenugreek gum > gum Arabic; the elastic and viscous performances of the four gums all have their respective strengths and weaknesses. All these differences in performance stem from differences in molecular structure, including significant differences in the shape of the molecular chains themselves and the state of mutual entanglement between molecular chains, which lead to gaps in actual performance. This study combined the analysis of thermal properties and rheological properties to establish a reference framework that allows for horizontal comparison, which can provide guidance for selecting suitable hydrophilic colloids for application scenarios that require heating processing, texture adjustment, and stability maintenance. Whether the production process requires high-temperature treatment, and texture of the product need to be adjusted, or the product needs to remain stable, this framework can be used as a reference to select the appropriate gum.