Development of an economically viable process for valorising Nannochloropsis oculata into bioactive proteins for cosmetic applications

The economic recovery of bioactive proteins represents a key barrier to the valorisation of microalgae for high-value cosmetic applications, particularly for Nannochloropsis oculata ( N. oculata ), which remains underexplored as a source of bioactive proteins despite its high biomass productivity. This study addresses this gap by developing a one-pot, process-intensified strategy that enables simultaneous cell disruption, selective protein precipitation, and phase partitioning in a single operation, thereby reducing downstream complexity and processing costs. An ultrasound-assisted three-phase partitioning (US-TPP) system was optimised to maximise protein recovery. Pentanol, combined with 20 wt% ammonium sulphate and a 1:1.5 salt solution-to-solvent ratio, yielded a separation efficiency of 88.2% and a protein recovery of 80.8% in the protein-rich middle phase. Cavitation-induced disruption eliminated the need for standalone pretreatment, as confirmed by FESEM imaging, which showed extensive cell rupture. The recovered proteins retained a cosmetic-relevant amino acid profile rich in leucine (14.82%), alanine (10.90%), and lysine (9.69%), alongside amino acids that promote collagen and moisturisation. Functional assays demonstrated strong antioxidant activity (IC₅₀ of 0.7 mg/mL for ABTS• + and 4.3 mg/mL for DPPH) and broad-spectrum photoprotection (λc = 391.07 nm). A preliminary techno-economic analysis (TEA) indicates that the US-TPP process markedly improves profitability compared to conventional methods. This improvement is driven by higher productivity, improved protein extraction yield, and increased antioxidant activity. Overall, the findings highlight US-TPP as a promising and economically viable approach for producing multifunctional, cosmetic-grade proteins from N. oculata , with potential integration into microalgal biorefinery frameworks.