Many seaweed species have a high production potential and attract interest as future protein sources. A high fiber and ash content, however, demand extraction of the protein to improve its digestibility and protein utilization in food or feed. This study explores three different approaches for protein extraction from Ulva fenestrata in order to maximize the protein extraction yield. Soluble protein was recovered either by mechanical pressing or by homogenization and osmotic shock of the biomass followed by alkaline extraction. The soluble protein was then concentrated by isoelectric precipitation. A combined procedure was carried out by pressing the biomass and following subjecting the residual pulp fraction to homogenization, osmotic shock and alkaline extraction. The three methods were ranked as follows with respect to protein extraction yield (as % of biomass protein); the combined method (23.9 ± 0.3%)> the alkaline extraction (6.8 ± 0.2%)> mechanical pressing (5.0 ± 0.2%). The significant increase when combining the methods was ascribed to a high precipitation yield after alkaline extraction of the pulp, hypothesized to be due to a reduced conductivity of the alkali-soluble protein fraction when derived from pulp rather than whole biomass.
