Rheological and Tribological Properties of Concentrated Guar Gum Mixed with Gum Arabic-based Emulsion

A conformational difference in gum arabic (GA) in aqueous and emulsion systems can influence its interaction with guar gum (GG). Therefore, in this study, the rheological and tribological properties of GG mixed with an orange oil emulsion containing GA at varying concentrations were investigated and compared with those of GG-GA mixtures. As the GA concentration was increased, the apparent viscosity of GG mixtures with either GA or GA-based emulsion (GAE) tended to decrease. Specifically, with a higher GA concentration (> 1.5%), the GG-GA mixtures showed a lower relative apparent viscosity than the GG-GAE mixtures. In contrast, except for GG-GA mixture with 6.0% GA, all other mixtures showed lower tan δ values (0.66–0.69) than GG alone (0.72), indicating an enhancement of weak gel-like properties. At a lower GA concentration (< 3.0%), GG-GA interactions in the aqueous system produced a lower relative tan δ value than those in the emulsion system, whereas the opposite result was observed with a higher GA concentration (> 4.5%). In addition, each type of mixture exhibited different tribological properties. As the GA concentration was increased, the friction coefficient (μ) values of both tended to decrease. Especially, the GG-GAE mixtures attained lower μ values than the GG-GA mixtures, thereby indicating that the former have better lubricant properties. These results demonstrated that the conformational change in GA while emulsifying oil droplets influences its interactions with GG.