Oil-in-water emulsions prepared using vegetable oils and buttermilk as emulsifier: Unveiling the impact of high-pressure homogenization valve design on emulsion physical and oxidative stability

This study investigated the influence of homogenization valve design and formulation parameters on the stability of oil-in-water emulsions produced with chia and sunflower oils (1:1) and buttermilk (BM) as the emulsifier. Three high-pressure homogenization techniques—microfluidization (MF), ultra-high-pressure homogenization (UHPH), and conventional homogenization (CH)—were compared at 100 MPa using buttermilk (5 and 7 %, w/v) and oil concentrations (10 and 20 % v/v). MF produced the most stable and uniform emulsions, characterized by the smallest droplet size and narrowest distribution, attributed to the effective control of droplet breakup in the homogenization chamber. UHPH produced fine but larger, less uniform droplets, reducing stability and increasing lipid oxidative susceptibility in the emulsions. This effect was attributed to intense shear forces and temperature rise at the UHPH valve outlet, which disrupted interfacial protein, causing partial denaturation and emulsion instability. CH emulsions, despite their larger droplet size, showed long-term physical stability due to droplet packing and surface charge density, which increased electrostatic repulsion but were the least oxidatively stable. Emulsion composition (BM and oil concentration) also played a critical role. In MF emulsions, higher BM concentration enhanced stability under low shear, whereas in UHPH systems, excess BM promoted protein aggregation under high shear. Increasing oil concentration (20 %) generally enhanced oxidative stability, attributed to viscosity effects and closer droplet packing that limited oxygen diffusion. Overall, the results highlight that both the homogenization technique and formulation composition must be optimized to balance physical and oxidative stability in chia/sunflower-BM emulsions, underscoring its potential for emulsion-based product development.