Subcritical Water for the Extraction and Hydrolysis of Protein and Other Fractions in Biorefineries from Agro-food Wastes and Algae: a Review

Low-cost plant and algal biomass are increasingly demanded as a source of proteins, and also, peptides and amino acids are gaining interest for their biological and functional properties. The reduction in chemicals, time and energy, and the integral valorization of the raw materials in the framework of biorefineries are major concerns in the development of environmentally friendly processes. Subcritical water technology is an efficient green technique useful both for extraction and for hydrolysis of protein and other fractions (lipid, carbohydrates, phenolics). However, adequate selection of operational conditions is needed in order both to maximize their extraction yield and to avoid degradation into monomeric units and decomposition products. This review summarizes the major features of subcritical water–based processes for the extraction/hydrolysis of protein. In order to valorizate other valuable fractions from agro-food wastes and algal biomass, optimal conditions should be established as a compromise solution. Alternatively, stagewise operation to sequentially obtain the target fractions could be desirable.