Integrated high-pressure and ultrasound assisted cascade processing for protein recovery from haddock fillet by-products

Lean fish by-products are an underutilized source of high-quality proteins, yet efficient bio-refinery strategies for recovery and valorisation remain limited. This study introduced an integrated cascade approach to improve protein recovery and valorisation efficiency from haddock ( Melanogrammus aeglefinus ) filleting by-products. Protein-rich fractions were first recovered by isoelectric solubilisation precipitation (ISP) to obtain fish protein isolates (FPIs), while the residual biomass was subsequently subjected to enzymatic hydrolysis to produce fish protein hydrolysates (FPHs). Sequential high-pressure processing (HPP)-ultrasound approach was applied under different conditions as intensification strategy. And a water-based extraction was evaluated as a greener alternative to conventional alkaline extraction. The highest total protein recovery (70.5 ± 0.01%) was achieved under alkaline extraction using 200 MPa HPP for 5 min, followed by 50% amplitude ultrasound for 10 min. Under the condition, the recovered FPI also exhibited optimal digestibility and antioxidant activity after INFOGEST digestion. This work demonstrates a potentially scalable and sustainable strategy for converting haddock by-products into value-added protein ingredients, supporting circular economy goals in the seafood industry.