From waste to resource: Production and characterisation of protein-enriched extracts from Gelidium corneum residue

This study aimed to develop protocols for extracting proteins from Gelidium corneum agar-extraction residue for their potential use in food-related applications. The residue was mostly composed of carbohydrates (41%), forming highly recalcitrant cell wall structures that hindered protein extraction through alkaline solubilisation. The application of high-pressure (350 MPa, 5 min, 20 °C) and ultrasound (10 min) pre-treatments did not induce significant microstructural changes in the biomass, but promoted the release of highly soluble proteins and peptides, increasing the protein extraction yields up to 10%, although the protein concentration in the extracts was not significantly improved. In contrast, the application of enzymatic hydrolysis combining carbohydrases (Vertera® Release) and proteases (Pancreatin) increased the extraction yield to 25% and concentrated the protein from 27% to 39%. While the native residue showed a very low protein digestibility (20%), this was significantly increased in all the extracts (around 80-85%). Overall, the enzymatic treatment proved to be the most promising strategy since it provided the highest extraction yields and the highest nutritional quality proteins, with a relatively high proxy Digestible Indispensable Amino Acid Score (DIAAS) value of 72. These results show the possibility of valorising the Gelidium corneum agar-extraction residue through alternative strategies for the production of extracts with high nutritional quality proteins.