Sustainable protein extraction technologies for the valorization and enhancement of a sunflower meal by-product as an alternative protein ingredient

Abstract

The continuous rise in global protein demand has increased interest in sustainable plant-based protein ingredients that can support future food production while reducing environmental impacts. Sunflower meal (SFM), a by-product of oil processing, contains approximately 30–50% protein on a dry-weight basis and remains underutilized. Conventional alkaline-based extraction can limit the food application of sunflower protein isolates (SFPI) by promoting protein denaturation, aggregation, and chlorogenic acid (CGA) oxidation, producing an undesirable dark green colour. This study investigated divalent salt-based, monovalent salt-based, and deep eutectic solvent (DES) extractions as sustainable alternatives for producing high-quality SFPI from commercial SFM. Alternative methods produced significantly higher protein purities, with MV-SFPI, DV-SFPI, and DES-SFPI containing 90.18%, 90.06%, and 88.46% protein, respectively, compared with 69.35% for ALK-SFPI. DES-SFPI achieved the highest extraction yield and protein recovery rate of 56.92% and 24.73%, respectively. Structural analysis showed greater aggregation and rearrangement in ALK-SFPI. DV-SFPI displayed the lightest off-white colour with an L* value of 84.07, while ALK-SFPI developed the darkest colour and a green hue. Techno-functional properties were influenced by extraction method and pH. MV-SFPI had the highest solubility at pH 7, DES-SFPI had the highest oil-holding capacity, and DV-SFPI showed the greatest foaming capacity under acidic and neutral conditions. Protein quality was further assessed through structural properties, amino acid composition, in vitro protein digestibility (IVPD), IV-PDCAAS, and anti-nutritional factors. All isolates retained characteristic 11S helianthinin and 2S albumin fractions but showed extraction-induced changes in secondary and tertiary structures. Amino acid profiles were comparable and rich in sulfur-containing amino acids, with lysine as the first limiting amino acid. IVPD remained high at 95.36%–98.75%. DV-SFPI had the highest IV-PDCAAS (62.91%), compared with 50.34% for ALK-SFPI. DES-SFPI had the lowest total phenolic content (5.30 mg GAE/g dry weight), while ALK-SFPI had the lowest trypsin inhibitory activity (0.045 TUI/mg DW). Overall, salt-based and DES extractions effectively valorized commercial SFM into high-quality SFPI with improved protein purity, recovery, extraction yield, colour, nutritional quality, and comparable or enhanced techno-functionality. These findings support SFPI as a sustainable alternative to traditional animal protein sources while promoting waste reduction and a circular economy.