Extraction of degraded proteins from red and green macroalgae using ultrasonic-assisted extraction and Fenton's reagent in combination

This study utilized two common macroalgae species from Taiwanese waters, green algae <i>Ulva lactuca</i> (<i>Ulva</i>) and red algae <i>Sarcodia suae</i> (<i>Sarcodia</i>), to evaluate the feasibility and efficacy of a novel cell wall disruption technique combining Fenton reagent and ultrasound-assisted extraction (UAE). The study analyzed protein characteristics, polysaccharide changes, and texture properties after pretreatment. Following cell wall disruption, the combined treatment of Fenton reagent and ultrasound significantly enhanced protein extraction yields, reaching 13.34 ± 0.50 % for <i>Ulva</i> and 3.96 ± 0.28 % for <i>Sarcodia</i>. In addition to increased yields, SDS-PAGE analysis and elevated free amino acid concentrations confirmed extensive protein degradation into low-molecular-weight peptides, indicating effective breakdown of protein structures. This enhanced degradation profile suggests that the pretreatment not only improves extraction efficiency but also promotes the production of functional protein hydrolysates. The surface hydrophobicity of the treated macroalgae significantly increased, while total and free sulfhydryl groups showed a decreasing trend, indicating that proteins were broken into smaller peptides, resulting in the destruction of sulfhydryl groups. To investigate the impact of the novel extraction technique on polysaccharides, the water-soluble total sugar and reducing sugar contents were measured. The disrupted <i>Sarcodia</i> samples showed total sugar and reducing sugar contents of 33.62 % and 2.76 mg/mL, respectively, while <i>Ulva</i> samples exhibited 27.00 % and 3.12 mg/mL, with significant increases observed in both macroalgae. Additionally, texture analysis and scanning electron microscopy (SEM) revealed that cell wall disruption enhanced the texture and compactness of the macroalgae. This study presents a high-efficiency cell wall disruption technique that effectively overcomes the challenges associated with macroalgae processing. By providing a robust scientific foundation, the research highlights the potential of macroalgae as valuable resources for food processing and plant-based meat production, while simultaneously contributing to sustainable practices and supporting efforts to reduce carbon emissions.