Emulsification Properties of Garlic Aqueous Extract: Effect of Heat Treatment and pH Modification

The aim of this study was to evaluate the emulsification properties of garlic water-soluble compounds (GWSC) after heat treatment (10 min at 95 °C) or pH adjustments (2.5, 3.5 and 7.8). After the various treatments, the extracts were used as such or filtrated (0.45 µm) and 10% soybean oil-in-water emulsions were prepared using low (0.48%) or high (6.55% wt/wt) extract concentrations. Whereas at low GWSC concentration, both heating or acidifying resulted in the formation of bigger oil droplet sizes (i.e. from d32=0.36 µm using unmodified extract, to d32=7–22 µm µm at pH 2.5 with or without extract filtration), the effects were opposite at the highest GWSC concentration. In the latter, heat treatment clearly reduced the droplet size as observed from the micrographs as well as the degree of creaming, though the occurrence of depletion and/or bridging flocculation was still strong. The acidification of the extract at this high GWSC concentration, significantly reduced the droplet size as observed from the micrographs but a strong flocculation was observed. Removal of protein aggregates, and possibly also saponin micelles from the extract, resulted in an obvious increase in emulsion droplet size. This research brings valuable insights on the study and utilisation of novel natural food emulsifiers from plant sources.