Assessment of Oxidative Stability in Fish Oil‐in‐Water Emulsions: Effect of Emulsification Process, Droplet Size and Storage Temperature

In this study, the effects of emulsification process, droplet size and storage temperature on the chemical and physical stability of Menhaden fish (Brevoortia tyrannus) based oil‐in‐water (O/W) emulsions were investigated, foreseeing the development of food emulsion systems with enhanced oxidative stability. For that purpose, the authors evaluated four different emulsification processes as follows: microchannel emulsification, premix membrane emulsification, vacuum homogenization and high‐pressure homogenization, and the droplets formulated had an average diameter ranging between 94 nm and 26.8 μm. For oil droplets sized within the micrometer range and stored at 5°C, decreasing the droplet size resulted in a significant increase on the oxidation activity (P < 0.01), which was expected considering that the increase in surface area likely leads the way to more oxygen diffusion toward the droplet surface onto the lipid core. On the contrary, for droplets sized within the submicron range, a linear relationship (R² = 0.91) between droplet sizes and the specific lipid oxidation rate was found. The results also indicate that other factors such as emulsifier type, emulsification process and storage temperature play major roles on lipid oxidation during emulsion storage. The spontaneous droplet formation in the case of microchannel emulsification resulted in emulsions with the lowest lipid oxidation compared with conventional homogenizers, which generally employ high energy input to disrupt the droplets, further promoting lipid oxidation. This study also revealed that lipid oxidation is strongly temperature‐dependent, since lipid hydroperoxide content in all O/W emulsions increased as the storage temperature increased. Among the emulsifiers tested, sodium oleate, an anionic emulsifier, was revealed as the most suitable candidate to suppress lipid autoxidation, especially considering the storage of food emulsions at room temperature. PRACTICAL APPLICATIONS: The insights on lipid oxidation presented herein may provide a liable source of information while designing and formulating oil‐in‐water emulsions containing antioxidant compounds, such as ω‐3 polyunsaturated fatty acids, with enhanced oxidative stability, foreseeing their potential application as functional foods or drug delivery systems. To the authors' knowledge, this is the first report relating to lipid oxidation in oil‐in‐water emulsions comprising different emulsification processes, resulting in fine oil droplets sized within a wide range, based on fish oil, a lipid highly prone to oxidation. The aspects of lipid oxidation kinetics presented here could have a potential economic contribution to the food emulsion industry while saving energy on the emulsification process or storage environment.