Insights into interactions between tragacanth gum and gum arabic in aqueous solutions: surface characteristics, viscosity and aggregation properties

Abstract

Tragacanth gum (TRG) and gum arabic (GA) are natural anionic gums with heterogeneous and distinctive macromolecular content. The aim of this study was to gain insight into interactions between compounds in TRG/GA mixtures and to clarify the physicochemical phenomena that occur. The following methods were used for this purpose: surface tension, fluorescence, viscosity and particle size measurements. Furthermore, the various solutions were monitored for phase separation. Surface tension measurements revealed that TRG had a lower critical aggregation concentration (CAC) value compared to GA (0.130% vs. 1.626%, respectively), and that with increasing TRG mass fraction in the mixtures, the CAC values decreased. The same trend was observed with overlapping concentrations (c*). Namely, c* values for TRG and GA were 0.224% and 3.297%, respectively, and the increase in TRG mass fraction caused the c* values to decrease. Additionally, it was noticed that the experimentally obtained values of specific viscosity deviate from the additive rule. The phase separation observation and the analysis of a separated phase indicated the formation of a coacervate-like phase, beginning at 2% GA in mixtures, around the CAC of GA. The mechanism responsible for the onset of these aggregates was proposed, as well as the compounds implicated in their emergence, and particle size analysis further highlighted complex interactions between TRG and GA. The results of this study could be used to guide the development of novel food, pharmaceutical, cosmetic and chemical products based on natural ingredients.