Abstract The influence of locust bean gum (LBG) on the physicochemical properties of model food sauces containing fat droplets was investigated. The particle size, microstructure, optical lightness, rheology, and storage stability of aqueous solutions and oil-in-water emulsions containing different LBG concentrations (0.05–1 wt%) were measured. Non-dissolved hydrogel microparticles were observed in both aqueous solutions and emulsions above a certain LBG level (≥0.4%). The mean particle diameter (d4,3) and apparent viscosity of the emulsions increased steeply when the LBG concentration exceeded about 0.2–0.4%, while the lightness and flocculation stability decreased. The emulsions were highly prone to creaming and phase separation at intermediate LBG concentrations (0.2–0.8%). The changes in the physicochemical properties of the emulsions with increasing LBG concentration were attributed to a number of factors: (i) viscosity enhancement; (ii) depletion flocculation; (iii) hydrogel formation. These results have important implications for the rational design and production of reduced-fat food emulsions, such as sauces, dressings, and deserts.