Cereal Chem 46:675 - 686. | VIEW
Lipid Oxidation in Full-Fat and Defatted Soybean Flakes as Related to Soybean Flavor.
D. J. Sessa, D. H. Honig, and J. J. Rackis. Copyright 1969 by the American Association of Cereal Chemists, Inc.
Extracting 99.8% of the oil from full-fat soybean flakes with pentane-hexane removed none of their green- beany, bitter flavor. This oil, with paraffinlike, vegetable-oil flavor, did not develop any further flavor on storage. Almost all the flavor and residual lipids from defatted soybean flakes were extracted by hexane- absolute ethanol azeotrope (79:21). The oil and azeotrope extracts had thiobarbituric acid (TBA) numbers of 5.8 and 34, respectively, which were computed from absorbance readings at 532 millimicrons. The oil and azeotrope extracts contributed about 10% to the TBA number of full-fat flakes. In both full-fat and defatted flakes, n-hexanal, acetaldehyde, and acetone represented the major volatile carbonyl compounds. These were characterized as 2,4-dinitrophenylhydrazones. No malonaldehyde derivative was obtained from the flakes. From defatted flakes, 3.6 p.p.m. carbonyl compounds were vacuum-stripped, but removal of this amount did not affect the original soybean flavor. Consequently, flavor of flakes could not be correlated with degree of oxidation as measured by TBA and volatile carbonyl compound analyses. Trace amounts of hydroperoxides appeared in lipid extracts from defatted flakes. When a soybean lipid extract, possessing similar composition to commercial soybean phosphatides, was UV-irradiated, the TBA number decreased from 67 to 33 and the flavor changed from that of paraffin and vegetable oil to that associated with rubber. Similar irradiation of commercial phosphatides generated TBA-reactive substances and bitter rancid flavors not characteristic of soybeans.