Characterization of the carbonyl compounds in reverted soybean oil^1,2,3

Abstract

Twenty-one mono-carbonyl compounds were identified in a reverted but not rancid soybean oil with a peroxide number of 2.7 meq/kg and a flavor score of 6.0. Six of the carbonyl compounds were saturated methyl ketones, ten were saturated aldehydes and five were 2-enals. The amount of 2,4-dienals in the reverted soybean oil was too small to be fractionated and identified. One fraction of the 2,4-dinitrophenylhydrazones of mono-carbonyl compounds obtained was different in chemical properties from those of the four known classes of compounds; viz. saturated aldehydes, saturated ketones, 2-enals, and 2,4-dienals. The chemical identity of this fraction has not been completely established.

The technique used for the identification of the mono-carbonyl compounds consisted of essentially five steps: (a) passing a hexane solution of the soybean oil through a celite column, which was homogeneously impregnated with 2,4-dinitrophenylhydrazine and phosphoric acid, in order to convert quantitatively all the carbonyl compounds in the oil into their 2,4-dinitrophenylhydrazones; (b) removing the soybean oil from the solution with a Seasorb-Celite Column; (c) removing decomposition products and 2,4-dinitrophenylhydrazones of ketoglycerides with an Alumnia Column; (d) separating, by adsorption chromatography, the 2,4-dinitrophenylhydrazones of mono-carbonyl compounds into four classes; viz. saturated ketones, saturated aldehydes, 2-enals, and 2,4-dienals; and (e) identifying the individual components in each class of compounds by the Rf values of liquid-liquid partition chromatography.