Protein Level and Particle Size-Dependent Stabilization of Oil-in-Water Emulsions by Sunflower Meal

Sunflower meal represents a protein- and fiber-rich by-product of the oil industry with potential application as a natural stabilizer in food emulsions. Building upon previous findings that emphasized the role of protein content in emulsion stability, the present study further investigated the combined effect of protein level and particle size distribution of sunflower meal fractions on the formation and stability of oil-in-water emulsions. Two sets of sunflower meal fractions were prepared from finely milled material, fractionated, and blended in controlled proportions to obtain four protein-enriched (30 ± 1%) and four cellulose-rich (15 ± 1%) fractions, each defined by particle size ranges of 250/200, 200/125, 125/100, and <100 µm. Emulsion stability was evaluated through droplet size analysis, zeta potential measurements, and creaming index determination during seven days of storage. The results demonstrated that both protein content and particle size significantly affected the emulsifying and stabilizing behavior of sunflower meal fractions. For the low-protein group (15%), larger particle sizes (250/200 µm) yielded smaller emulsion droplets (D[4.3] = 66.03 µm) and higher zeta potential values (−15.53 mV), while in the high-protein group (30%), droplet size distribution was more uniform (D[4.3] from 72.13 to 76.29 µm). During seven days of storage, all emulsions exhibited a gradual increase in creaming index, followed by partial stabilization at later time points. Emulsions prepared with sunflower meal fractions of higher-protein content showed consistently lower creaming index values, indicating improved physical stability throughout storage. Overall, the study confirmed that the interplay between composition (protein level) and physical structure (particle size) governs the emulsification efficiency of sunflower meal fractions, providing insights for their potential application as plant-based stabilizers in food systems.