Palmaria palmata as an alternative protein source: enzymatic protein extraction, amino acid composition, and nitrogen-to-protein conversion factor

The red seaweed Palmaria palmata has previously been reported to have high protein content high in essential amino acids. To extract the proteins a rigid cell wall consisting mainly of β-(1→4)/β-(1→3)-D-xylans must be disrupted. Different methods have been used to overcome this problem along with various methods used for protein evaluation. In this study, the effect of enzymatic pre-treatment on protein extraction was examined. Both enzymatic hydrolysis with xylanase and protease were tested. The amino acid content of the fractions was examined after extraction. The amino acid composition was similar to what has previously been reported; P. palmata was high in essential amino acids. Accordingly, a nitrogen-to-protein conversion factor was calculated for each fraction individually and protein results were compared with calculation using the proximate 6.25 conversion factor. The nitrogen-to-protein conversion factor varied between fractions but all factors were significantly lower than the popularly used 6.25 indicating that this conversion factor for processed P. palmata is effectively and considerably overestimating the protein content. Enzymatic pre-treatment with xylanase resulted in enhanced amino acid content and successful protein extraction. Enzymatic hydrolysis using protease resulted in higher protein content in the liquid extract compared to hydrolysis with xylanase, due to the release of proteins, peptides, and amino acids. Therefore, hydrolysis with protease is not suitable to extract proteins from P. palmata with the method described within this study but might be an optimal method to examine the bioactivity by extracting the protein hydrolysates. However, the result from this study confirm that hydrolysis with xylanase is a feasible choice to extract proteins of good quality from P. palmata.