Extraction mechanisms of proteins from Palmaria palmata

Protein extraction from Palmaria palmata remains challenging due to structural features that restrict protein release. This study evaluated alkaline solvents, xylanase enzymes, and deep eutectic solvents (DES) to assess protein recovery and structural changes using chemical analysis and microscopy. Protein yield, sugar solubilization, tissue density, protein localization, and cell wall integrity were examined. Microscopy revealed that proteins are concentrated in densely packed cortical cells with minimal intercellular space, limiting solvent penetration. Alkaline extraction achieved the highest protein recovery (~60%) with moderate structural disruption. Xylanase-assisted extraction caused greater cell wall breakdown but resulted in lower protein recovery (~27%), while DES treatment caused minimal disruption and yielded the lowest recovery (~14%). Carbohydrate solubilization did not correlate with protein recovery, indicating that cell wall degradation alone is insufficient. These findings identify dense cortical organization as a key constraint and highlight the need for combined mechanical and targeted biochemical strategies to improve extraction efficiency. • Microscopy confirms that acidic tissues are concentrated in the cytoplasm of high-density tissue in the photosynthesis-active region/cortex. • Structural assembly acts as a natural barrier to solvent penetration into the cytoplasm. • Alkaline treatment achieves the highest protein extraction yield by isolating more tissues in the cortical and medulla region. • Xylanase hydrolyzes most of the main cell wall constituents but fails to extract high levels of protein. • Deep Eutectic Solvent (DES) extraction shows minimal disruption of biomass and the lowest protein yield.