Surface active material and process for preparing same

A method of producing a surface active material comprising (1) phospholipid, neutral fat, total cholesterol, free fatty acids, carbohydrate, protein and water, all of which are obtained from the lung tissue of a mammal, and (2) optionally at least one additional component selected from the group consisting of a phosphatidylcholine, a neutral fat and a free fatty acid, characterized in that the overall phospholipid content is 68.6-90.7%, the overall neutral fat content is 0.3-13.0%, the total cholesterol content is 0.0-8.0%, the overall free fatty acid content is 1.0-27.7%, the carbohydrate content is 0.1-2.0%, the protein content is 0.0-3.5%, and the water content is 2.1-5.2%, all based on the dry weight of the material, the surface tension of the material as measured at 15.degree.-25.degree. C. by Wilhelmy's method in which the material is added dropwise to the surface of physiological saline in an amount of 0.3-0.8 .mu.g per square centimeter of the surface area thereof being 30.1-47.5 dynes/cm when the surface area is 54.0 cm.sup.2, the method comprising the steps of:

• (a) bringing the minced lung tissue of a mammal into contact with an electrolyte solution to obtain an extract;
• (b) centrifuging the extract to collect a crude sediment;
• (c) adjusting the specific gravity of an aqueous suspension of the crude sediment by the addition of sodium chloride and centrifuging the adjusted suspension to isolate a top layer comprising an emulsified scum layer;
• (d) dialyzing an aqueous suspension of the top layer and lyophilizing the dialyzed suspension to obtain a crude dry product;
• (e) bringing the crude dry product into contact with an acetic acid ester to collect a material insoluble in the acetic acid ester and then bringing the insoluble material into contact with an organic solvent mixture to obtain a purified filtrate;
• and
• (f) concentrating the purified filtrate to obtain a solid residue, optionally adding to the solid residue at least one additional component selected from the group consisting of a phosphatidylcholine, a neutral fat and a free fatty acid, so as to provide an overall phospholipid content of 68.6-90.7%, an overall neutral fat content of 0.3-13.0%, and an overall free fatty acid content of 1.0-27.7%, all based on the dry weight of the final product, at well as an overall phosphatidylcholine content of 58.4-85.0% based on the total weight of phospholipid, and then lyophilizing the resulting mixture.