Mustard seed protein isolates are produced at a high purity level of at least about 100 wt % (N×6.25) by a process wherein mustard seed protein is extracted from mustard seed meal, the resulting aqueous mustard seed protein solution is concentrated to a mustard seed protein content of at least about 200 g/L, and the concentrated mustard seed protein solution is added to chilled water having a temperature below about 15° C. to form mustard seed protein micelles, which are settled to provide a mustard seed protein micellar mass (PMM). The mustard seed protein micellar mass is separated from supernatant and may be dried.