Physical and Oxidative Stabilization of High Internal Phase Emulsions using Flaxseed Press Cake Powder as a Direct-Use Ingredient: An Extraction-Free Shortcut

Flaxseed press cakes (FPCs), a by-product of cold-pressed oil extraction, are a rich source of bioactive and functional compounds. However, their valorization relies on costly and time consuming extraction processes. This study evaluated powdered FPC as a scalable, dual-functional ingredient for the physical and oxidative stabilization of high internal phase emulsions (HIPEs), as a basic food model system for potential future formulations. To this end, powdered FPCs were sieved into three particle sizes, namely ≤0.21, >0.21–0.50, and >0.50–1.00 mm. Chemical and structural characterization indicated that the larger fractions may contain more hull-derived material, whereas the finest fraction may contain more inner-seed tissue. The finest fraction had the highest protein content, while the larger fractions exhibited a higher phenolic content, antioxidant activity, emulsifying capacity, and high-molecular-weight polysaccharide content. HIPEs, formulated with 73% w/w soybean oil and 2% w/w FPCs, were evaluated for droplet size, ζ-potential, and rheological properties. The firmness and elastic modulus (G′) of HIPEs stabilized with ≤0.21 mm FPCs increased from 4.24 ± 0.74 N and 173.97 ± 4.26 Pa, respectively, to almost twice these values in HIPEs stabilized with the larger particles. All samples showed gel-like, shear thinning behavior and maintained stable droplet sizes during the 7-day storage period. Under iron catalyzed oxidation at room temperature for 168 h, the larger FPC fractions provided the strongest protection against lipid oxidation. These findings demonstrate the potential of powdered FPC as a multifunctional, natural, clean-label ingredient for stabilizing emulsion-based foods while providing a simple and sustainable strategy for upcycling oil-extraction by-products.