A procedure which comprises a second step of pressing of the Salvia Hispanica L. seeds with temperature control modifying the ratio between the polyunsaturated fatty acids and antioxidants contained as well as obtaining an expeller.The procedure comprises a third step in which the expeller obtained is let to cool until it reaches room temperature and a fourth step in which the expeller, at room temperature, is entered into a disc-driven mill to obtain different particle sizes of a partially low-fat flour with a high content of polyunsaturated fatty acids, especially .OMEGA..sub.3 type.