Optimization of pulsed electric field pretreatment followed by cellulase hydrolysis for enhanced protein recovery and antioxidant activity from brown seaweed (Undaria pinnatifida)

Undaria pinnatifida is a promising brown seaweed due to its relatively high protein content and functional bioactive compounds. However, efficient recovery of these components is limited by its rigid, polysaccharide-rich cell wall structure. In this study, pulsed electric field (PEF) treatment followed by cellulase hydrolysis was investigated as a sequential approach to enhance protein extraction and antioxidant functionality from U. pinnatifida. PEF conditions were optimized by varying electric field strength, pulse width, pulse repetition frequency, treatment duration, seaweed loading, and pretreatment conditions to maximize protein release. The optimized conditions were 3 kV cm−1 electric field strength, 10 µs pulse width, 100 Hz pulse repetition frequency, and 60 s treatment duration, using 100 g of seaweed pretreated by mechanical cutting followed by 2 days of soaking in 3.5% saline solution. Under these conditions, protein concentration reached 493 ± 2.06 µg mL−1. The optimized PEF treatment required 0.18 kJ of electrical energy and achieved an energy efficiency of 684.72 ± 2.78 mg protein kJ−1. Subsequent cellulase hydrolysis further enhanced protein extraction, with the PEF + 1% cellulase treatment yielding 1307 ± 38.62 µg mL−1, compared with 870 ± 42.38 µg mL−1 for 1% cellulase alone, 512 ± 15.94 µg mL−1 for PEF alone, and 275 ± 10.46 µg mL−1 for the untreated control. Thus, the combined treatment produced approximately 50%, 155%, and 375% higher protein concentrations than 1% cellulase alone, PEF alone, and the untreated control, respectively. Antioxidant activity assessed separately using DPPH, ABTS, and FRAP assays also showed the highest responses for the combined treatment, with 52.08 ± 2.68% DPPH radical-scavenging activity, 51.00 ± 1.08% ABTS radical-scavenging activity, and 679 ± 1.08 µM Fe2+ equivalents in the FRAP assay. Overall, the optimized sequential PEF–cellulase treatment substantially improved protein extraction and produced the highest antioxidant responses among the treatments investigated, demonstrating its potential for enhancing the recovery of protein and antioxidant-active components from U. pinnatifida under laboratory-scale conditions. Optimal PEF conditions included 3 kV cm−1, 10 µs, 100 Hz, and 60 s. Cutting followed by 2-day soaking in 3.5% saline water yielded 493 ± 2.06 µg mL−1 protein after PEF. Optimized PEF required 0.18 kJ and achieved an energy efficiency of 684.72 ± 2.78 mg protein kJ−1. PEF followed by 1% cellulase increased protein concentration to 1307 ± 38.62 µg mL−1. PEF + cellulase achieved 52.08 ± 2.68% DPPH and 51.00 ± 1.08% ABTS radical-scavenging activity. PEF + cellulase produced the highest FRAP response at 679 ± 1.08 µM Fe2+ equivalents.