Summary
Amino‐hexose‐reductones were evaluated as antioxidants in soybean, cottonseed, and corn oils and were shown to be highly effective by all oxidative and chemical tests. The activity of the eight different reductones was approximately the same in any one substrate. Slightly higher activities were given by reductones of lower molecular weight. Activity was demonstrated at concentrations as low as 0.001% and was shown to be a linear function of the concentration up to 0.02%, the approximate limit of solubility. Out‐standing features of the reductone‐treated oils were long induction periods, slow absorption of oxygen, and low rates of peroxide development. Reductones are believed not to react directly with peroxides but to prevent peroxide formation by reacting with some precursor.
The combination of reductones with other antioxidants showed synergistic effects in only one sample of corn oil. The activity of combinations in soybean and cottonseed oils was for the most part strictly additive. In soybean oil, citric acid‐reductone combinations with each at the 0.01% level gave a slight improvement over the expected activity. Oils stabilized with multiple‐component, antioxidant mixtures in which an amino reductone replaced propyl gallate showed less peroxide development and were equally acceptable according to organoleptic scores. Aged oils did not show the organoleptic improvement that would be expected from the marked improvement observed in the oxidative stability. Significant improvements in flavor stability could be observed with reductones only when they were used in combination with an‐other antioxidant. Reductone‐treated soybean and cottonseed oils did not show an appreciable improvement in flavor stability. Only the di‐n‐butylamino‐and diallylamino‐reductones contributed foreign flavors to the oil. Atypical flavors are believed associated with the amine moiety of the reductone.
At high temperatures and at higher concentrations of reductones a brown melanoid color develops in the oil. The anhydro derivatives developed more color than the normal reductone. The reductones do not withstand oil deodorization conditions.
Destruction of tocopherols during autoxidation of fats was studied to gain more information about the mechanism of their antioxidant action. Tocopherol loss during autoxidation was much smaller in the highly unsaturated vegetable oils than in cottonseed oil and lard. Metal contaminants increase appreciably the extent of tocopherol oxidation. Their effect is eliminated by the addition of 0.01% citric acid. The work suggests that the hydroperoxides formed in the highly unsaturated vegetable oils decompose rapidly before they react with tocopherol. Antioxidants that react more rapidly than tocopherol with polyunsaturated fat hydroperoxides are needed to stabilize highly unsaturated vegetable oils.
SummaryFlavor and oxidative stabilities of furfural‐fractionated soybean oils have been evaluated. The raffinate fractions did not develop the off‐flavors typical of soybean oil as did the extract and original oil samples. The raffinate fractions have a low resistance to oxidation, but the addition of stabilizers improved the oxidative stability. Among the stabilizers tested were phosphatides, α‐tocopherol, and citric acid. Citric acid and phosphatides are believed to function in part as metal scavengers.
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