Development of chia oil-in-water nanoemulsions using different homogenization technologies and the layer-by-layer technique

Aim: The present study investigates the influence of various homogenization techniques, namely high-pressure valve homogenization and microfluidization, and different forms of modified sunflower lecithin, including deoiled (DL) and hydrolyzed (HL) variants, on the development of monolayer and bilayer nanoemulsions of chia oil. Methods: Oil-in-water (O/W) nanoemulsions with 5% chia seed oil were prepared using simple (0.5% DL or HL) or double-layer [0.5% DL or HL and 0.3% chitosan (Ch)] stabilization. This involved a two-step homogenization process, utilizing either microfluidization or high-pressure valve homogenization. Chia oil nanoemulsions were characterized by their zeta potential, particle size, and rheological properties. Besides, their physical stability and omega-3 content during refrigerated storage were evaluated. Results: Overall, the studied modified sunflower lecithin (DL and HL) demonstrated effective capability in stabilizing chia nanoemulsions and facilitating the formation of the double-layered structure following Ch deposition. Concerning the homogenization method, it has been demonstrated that under the same homogenization conditions, microfluidization resulted in significantly smaller droplet sizes and higher apparent viscosities compared to high-pressure valve homogenization. This discrepancy can be attributed to the design of the homogenization chambers, as microfluidization generates a narrow distribution of shear forces, while high-pressure valve homogenization yields a much broader distribution. In contrast to chia monolayer nanoemulsions, the nanoemulsions stabilized by modified sunflower lecithin-Ch demonstrated a noteworthy improvement in their overall stability. This enhancement can be ascribed to their increased apparent viscosity and the highly charged interfaces of the droplets. Furthermore, throughout the entire refrigerated storage period, the omega-3 content in all nanoemulsions remained unchanged. Conclusions: In this study, mono and bilayer chia oil nanoemulsions were successfully obtained using modified sunflower lecithin and high-energy techniques. Microfluidization outperformed high-pressure valve homogenization, resulting in smaller droplets and increased viscosity. These findings are relevant for designing stable