Abstract: The invention is directed to a process for preparing a library of saposin lipoprotein particles, wherein the particles comprise membrane components from a cell or an organelle membrane and a lipid binding polypeptide that is a saposin-like protein belonging to the SAPLIP family of lipid interacting proteins or a derivative form thereof, wherein the process comprises the steps of a) providing a mixture of crude membrane vesicles obtained from a cell or an organelle membrane; b) contacting the mixture of step a) with the lipid binding polypeptide in a liquid environment; and c) allowing for self-assembly of the particles. The invention also provides a process for preparing a purified saposin lipoprotein particle comprising the steps of preparing a library according to the process described above and the additional step of f) purifying the saposin lipoprotein particle from the library.