Improved quality of soybean oil from fine soybean flour by solvent extraction

Measurements of rates of extraction in a column with either fine flour or soybean flakes showed that in the flour extraction the oil was being washed out of the fine flour with little diffusion involved, whereas with flakes the limit on extraction rate was diffusion of the solvent into and out of the tissue.; Fine full fat flour worked very well in a laboratory batchwise countercurrent extraction with mixing and centrifugal separation. The oil resulting from this countercurrent extraction system had superior quality with very little phospholipids and free fatty acids and was light in color. However, due to the large hold-up volume, the separation of miscella from the meal required several stages to finish.; Aqueous ethanol solutions were used as a second solvent to displace the hold-up volume of hexane miscella. But the second solvent did not remove all the oil extracted by hexane. A test with beta-carotene showed that only the hexane miscella outside the flour particles was displaced.; Aqueous ethanol solutions as a second solvent extracted additional nontriglyceride materials (primarily phospholipids) from the meal. The quality of the extracted crude oil was lowered although only one centrifugation was needed.; A continuous extraction system with fine flour was tested at a laboratory scale with no success due to lack of proper ways to move dry flour, to mix the flour with solvent and to separate the solid from miscella. A pilot plant study showed that the grinding of beans and the separation of solid from miscella are the most difficult steps in solvent extraction with fine flour. The oil from the pilot plant study showed very low phospholipids content as did the laboratory extraction. But the free fatty acid content and color of the oil were abnormally high.; More laboratory studies revealed that moisture levels of the beans and of the flour affect the phospholipid and free fatty acid content of the resulting oil. But the reasons for the abnormally high free fatty acid content and dark color of the pilot plant extracted oil are still unknown.