Functional protein extraction from brown seaweed from the North Sea?

Samenvatting

The aim of this project was to investigate whether it is possible to extract functional proteins for human application from brown seaweed from the Dutch North Sea. To achieve this, knowledge about the molecular cell structures, location and function of proteins in seaweeds is essential. In brown seaweed, the cell wall mainly consists of a carbohydrate network of alginate, fucoidan and cellulose. Proteins have various functions and are located in different places in the cell. Roughly speaking, we can distinguish between glycoproteins, enzymes and proteins built into photosystems. Glycoproteinsare protein-sugar compounds that are located in the cell walls and give the cell wall rigidity. Photosystems are complex structures for capturing light which are located in the cell membranes. The enzymes are located freely in the cells, are water-soluble and in this way relatively easy to isolate. To recover all these proteins the carbohydrate network in the cell wall must be broken open.It was investigated whether it is possible to extract proteins from the seaweed species Saccharina and Undaria by means of a combined mechanical and enzymatic treatment. After only mechanical treatment, the protein yield in the liquid fraction was comparable for both seaweeds (~35%(protein/total protein)). The protein content in Undaria was higher (14 vs 10% (protein/DW) in Saccharina) which also resulted in a higher protein content (8 vs 5% (protein/DW)) in the liquid fraction. These recoveries and compositions are insufficient for a commercially viable process (targetprotein recovery >80% and protein composition >40% (protein/DW)). By making a gel using the secrude extracts, it was shown that the liquid fractions had gelling capacity and are therefore potentially interesting as functional ingredients for food application.An attempt was made to open more cells by means of a combined mechanical and enzymatic treatment. Commercial carbohydrases were used for this, which are enzymes that break downcarbohydrates, but leave proteins untouched. The protein yield for Saccharina was increased to ~40%(was 35%) and the protein content to ~7% (was 5% (protein/DW)). Microscopy showed that the majority of the cells were still intact, meaning that the combination of mechanical and enzymatic treatment did not completely break the cells open. The explanation for this limited effectiveness is that commercially available carbohydrases are suitable for breaking down complex carbohydrate compounds in land plants such as cellulose and hemicellulose. Carbohydrases that can break down complex carbohydrate compounds in seaweed are currently not commercially available. Such enzymes exist and are present in fungi that naturally grow on seaweed: seaweed biomass is broken down in the marine environment. Together with NIOZ and Westerdijk Institute, a new project was started in 2022,aiming at isolating specific enzymes from marine fungi that are able to break down the cell walls in seaweeds. This project is part of the NWO program “From Sea to Society”.