Emulsification properties of garlic aqueous extract

Abstract

The aim of this study was to evaluate the emulsification properties of garlic water-soluble compounds, currently non-existing in the literature. Compositional analysis along with surface tension measurements were carried out on the garlic aqueous extract, followed by the evaluation of 10% oil-in-water emulsions made with this extract at various concentrations. Microstructural analysis—droplet size by static light scattering, and light, confocal and transmission electron microscopy—along with phase separation measurements of the emulsions under storage, were also investigated. Whereas surface tension decreased with increasing garlic extract concentration, the lowest concentration (0.48% wt/wt) produced the smallest oil droplet size (d32 = 0.36 μm) increasing up to d32 = 6.55 μm at the highest extract content (6.55% wt/wt). Microstructural analysis also indicated the occurrence of depletion and bridging flocculation phenomena with increasing garlic extract concentrations, apart from obtaining bigger initial droplet sizes. Compositional analysis revealed that the ratio of saponins:fructans:proteins could be playing a key role in the droplet size distributions obtained, as confocal scanning laser microscopy and transmission electron microscopy also indicated differences at the interface when changing concentrations. Creaming was observed over time in all the emulsions but it was more evident with increasing garlic concentration. Beside flocculation, coalescence also took place after one-day storage at low and high concentrations. The underpinning reason of these phenomena can be related to the coexistence of compounds of different surface-active nature (i.e. a combination of saponins, proteins/peptides and fructans), and their interactions. This research brings valuable insights on the study of novel natural food emulsifiers from plant sources.