Properties and stability of oil-in-water emulsions stabilized by fish gelatin

The influence of molecular weight on the ability of fish gelatin (FG) to form and stabilize oil-in-water emulsions was examined. Low molecular weight fish gelatin (LMW–FG, ∼55 kDa) and high molecular weight fish gelatin (HMW–FG, 120 kDa) were used to prepare 20 wt% corn oil-in-water emulsions (pH 3.0, 10 mM imidazole-acetate buffer). Emulsions with monomodal particle size distributions and small mean droplet diameters (d43≈0.35 μm for LMW–FG and 0.71 μm for HMW–FG) could be produced at protein concentrations ≥4.0 wt%. However, optical microscopy showed that there was always a small population of large droplets present in the emulsions after homogenization and some oil destabilization (≥2 wt%). The presence of these large droplets was attributed to the relatively low surface activity (c1/2=0.1–0.2 wt%) of fish gelatin compared to globular proteins such as β-lactoglobulin (c1/2=0.004 wt%). Emulsions stabilized by LMW–FG contained a bigger population of large droplets than HMW–FG emulsions, but were more stable to creaming, which was attributed to depletion flocculation. Fish gelatin stabilized emulsions remained moderately stable to droplet aggregation and creaming after they were subjected to changes in holding temperature (30 or 90 °C for 30 min), salt concentration (NaCl≤250 mM) and pH (3–8). This study demonstrates that fish gelatin may have some limited use as a protein emulsifier in oil-in-water emulsions.