The present invention relates to the large-scale fractionation and isolation of peptides, polypeptides and protein(s) from a potato derived protein solution such as potato extract, potato fruit juice and fruit water using an adsorbent coupled with a ligand for the capture of the protein(s), from the protein solution. In particular the invention relates to a process for the isolation and separation of patatin and potato protease inhibitors using a low temperature non-denaturing process.