Flaxseed press cake particles as multifunctional stabilizers for high internal phase emulsions

The growing demand for sustainable and clean-label food ingredients has stimulated interest in valorizing agro-industrial by-products as functional ingredients. Flaxseed press cake (FPC), a by-product of cold-pressed flaxseed oil extraction, is rich in proteins, polysaccharides, and phenolic compounds that may provide both emulsifying and antioxidant functions. This study investigated the effect of coarse FPC powders at different particle sizes (≤0.21, ≤0.50, and ≤1.00 mm) on the physical and oxidative stability of the high internal phase emulsions (HIPEs). FPC fractions were first characterized for functional and chemical properties, including water-holding capacity, oil-binding capacity, emulsifying activity and stability indices, total phenolic content, antioxidant activity, and protein profile to estimate their potential as an ingredient to formulate HIPEs. The FPC particle fractions at a concentration of 2% (w/w) were then utilized to develop 73% (w/w) soybean oil-in-water HIPEs. The prepared HIPEs were evaluated for rheological behavior, texture profile, droplet size distribution, zeta potential, microstructure, color stability, and oxidative stability. The results showed that particle size fractionation significantly affected both the functional properties of FPC and the characteristics of the resulting emulsions. Larger FPC fractions exhibited greater water-holding capacity, total phenolic content, and DPPH radical scavenging activity, indicating improved preservation of bioactive compounds. All HIPEs displayed non-Newtonian pseudoplastic (shear-thinning) behavior and maintained stable emulsion structures. Emulsions prepared with the ≤0.50 and ≤1.00 mm fractions exhibited significantly greater firmness, consistency, cohesiveness, and viscosity than those stabilized with the finest particles. Microscopic observations and droplet size measurements confirmed compact droplet networks with no evidence of phase separation. Oxidative stability measurements showed that larger particle fractions generally exhibited improved resistance to lipid oxidation, consistent with their higher antioxidant capacity. These findings demonstrate that FPCs can serve as an effective multifunctional ingredient, simultaneously providing emulsification, structural reinforcement, and antioxidant protection in HIPE systems. These results highlight the potential of minimally processed FPCs as a sustainable, clean-label ingredient for developing stable emulsion-based food products while contributing to the valorization of oilseed processing by-products.