Patricia M. Cooney

Effect of autoxidation prior to deodorization on oxidative and flavor stability of soybean oil

SummaryOxidation prior to deodorization was shown to be detrimental to the flavor and oxidative stability of soybean oil. The increase in the nonvolatile carbonyl content of freshly deodorized oils was proportional to the peroxide value of the oils before deodorization. Rate of loss of flavor and oxidative stability of the oil were related to the extent of carbonyl development. All oils, whether or not they had been submitted to any known oxidation, contained some nonvolatile carbonyls. The loss in stability was not due to a loss of the antioxidant tocopherol.Oxidized soybean oil methyl esters were shown to develop nonvolatile carbonyl compounds upon heating at deodorization temperatures. The addition of isolated methyl ester peroxide decomposition products to deodorized soybean oil reduced its flavor and oxidative stability in proportion to the amount added. The results obtained were parallel and similar to those obtained by oxidizing soybean oil prior to deodorization.Flavor deterioration and undesirable flavors were typical of aging soybean oil whether or not the oils were oxidized before deodorization or whether an equivalent amount of nonvolatile thermal decomposition products was added to the oil. These oxidatively derived, nonvolatile carbonyl materials are believed to enter into the sequence of reactions that contribute to flavor instability and quality deterioration of soybean oil. The structure of these materials is not know.This work indicates the importance of minimizing autoxidation in soybean oil particularly before deodorization to insure good oxidative and flavor stability.

Influence of heat on oxidative stability and on effectiveness of metal-inactivating agents in vegetable oils

SummaryMetal-inactivating agents, such as citric acid, sorbitol, lecithin, and carboxymethylmercapto succinic acid, are not active in unheated vegetable oils. Apparently trace metals present in normal glyceride oils are held within a complex of unknown structure. After heating an oil, the metals can be complexed by metal-inactivating agents, such as citric acid. The release of metals appears to be associated closely with the breakdown of the fatty acid hydroperoxides. Formation of some association or complex between the metal and the hydroperoxide group or between the metal and the unsaturated linkage of the fatty hydroperoxide is suggested. The metals are held very tenaciously within this unknown structure. Although the metal is not available as an uncomplexed metallic ion, it does behave as a very strong pro-oxidant catalyst. The application of heat releases the metal so it can be complexed by added metal inactivators.

Soybean “lecithin” and its fractions as metal-inactivating agents

SummaryThe addition prior to deodorization of 0.1% of either crude phosphatides, or the alcohol-soluble, or the alcohol-insoluble fraction all improved the oxidative stability and the initial flavor of soybean salad oil. However all three additives caused significant darkening of the oils and the introduction of undesirable storage flavors when added at levels which improved the oxidative stability.High-sugar fractions from the crude phosphatides did not darken the oil nor did they confer improved oxidative or flavor characteristics.Cadmium-precipitated lecithin and inositol-phosphatidic acids containing no amino nitrogen gave lower color to salad oils upon deodorization than did the amino-nitrogen-containing phosphatides.Purified cadmium-precipitated lecithin had little effect upon the oxidative stability when added at levels below 0.02%. A significant improvement results from the addition of 0.05%, and oxidative stability shows further improvement by raising the level to 0.1%; however no increase in stability was obtained by raising of the concentration above this level.At concentrations of 0.01 and 0.05%, cadmium-precipitated lecithin had little effect on the color of the oil. At levels of 0.1 and 0.2%, significant darkening of the oils occurred though much less than with the amino-nitrogen-containing phosphatides.Based on the flavor responses of oils to which these phosphatides were added, it appears that phosphatides constitute the precursors for the melony, bitter, cucumber flavors frequently encountered in aged soybean salad oils. These flavor responses are the same as those obtained from added phosphoric acid.

Metal inactivation in edible oils by carboxymethylmercapto succinic acid

SummaryCarboxymethylmercapto succinic acid was one of the most effective metal inactivators examined for use in glyceride oils. The effectiveness is based on oxidative A.O.M. peroxide tests and on the organoleptic evaluation of various types of oils and shortenings. Indexes as high as 80-fold have been observed in preventing peroxide development. Extensive taste panel evaluations have shown significant improvements in the initial flavor and flavor stability of oils and shortenings treated with this mercapto acid. Indications are that the material has an extremely low order of toxicity. Acute tests have shown that the toxicity of the sodium salt is less than that of sodium citrate.The thermal instability to withstand deodorization temperatures and the possibility of the development of a mercaptan odor and taste in oils subjected to a high temperature is a serious disadvantage. Under some conditions the low order of fat solubility and the poisoning of hydrogenation catalyst would be detrimental in some oil-processing operations.Carboxymethylmercapto succinic acid and its derivatives may find use in salad oils, special hydrogenated oils for candy, icing, etc., vitamin preparations, drugs, and similar products where excellent trace metal-inactivating properties are required and where exposure to high temperatures is not encountered.

The flavor problem of soybean oil. XII. Nitrogen coordination compounds effective in edible oil stabilization

SummaryMetal deactivating agents containing nitrogen as the coordinating atom have been developed for use in edible oils. The most effective compounds were those containing two carboxyl groups, α,α′ to the nitrogen. Those containing β,β′ carboxyls were less effective, and the efficiency of α,β carboxyls was intermediate. The activity is explained on the basis of the formation of metal chelation rings—complexes believed to be typical Werners coordination complexes. The nitrogen atom may be an amine or a cyclic nitrogen. Complex coordination compounds can also be formed from acidic nitrogen compounds, such as hydroxamic acids, when the proper structure for metal chelation exists.Chelidamic acid has been found to be a very efficient metal deactivating agent for both copper and iron. Imino α or β dicarboxylic acids show varying degrees of effectiveness toward the complexing of iron and copper. The greater the number of 5-membered chelation rings that are possible around the metal atom, the greater is the observed stability.

The flavor problem of soybean oil. VI. Flavor and oxidative stability of furfural-fractionated oil

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.

Citric acid: Inactivating agent for metals or acidic synergist in edible fats?

Oxidative stabilities of soybean oil and lard are improved by the addition of either sorbitol or citric acid. Sufficient sorbitol gives enough improvement in stability so that added citric acid gives no increased stability. Unless sorbitol acts as a neutral synergist, forms a powerful acidic synergist in trace amounts or a new antioxidant, the antioxidant activity of citric acid appears to come from its inactivating capacities for metals.

Determination of tocopherol in oxidized fats. Interference from heat-formed reducing substances in highly oxidized fats.

Summary and ConclusionsBy application of a heating method to determine tocopherol in oxidized fats it was shown that polymeric reducing substances were produced when fats have a peroxide value exceeding 100. By comparison with a chromatographic method to remove peroxides it was shown that the interference in determining tocopherol from these heat-produced reducing substances was negligible at peroxide levels lower than 100. It is concluded that the heating method is satisfactory within the peroxide range (0–100) most important in oxidative and flavor-stability studies of edible oils. The chromatographic method for removing peroxides can be relied upon for determining tocopherol in more highly oxidized fats as well as in methyl esters of fatty acids which are distillable under conditions of the heating method.The appearance of reducing substances in heated oxidized fats is related to the peroxides present in the fats prior to heating. It is accompanied with an increase in browning, viscosity, acid, and carbonyl values of the fats and with a decrease in iodine values. The polymeric material from heated-oxidized methyl esters of unsaturated fatty acids has been separated by vacuum distillation and chromatography on silicic acid. It is believed to be principally dimeric in nature.

Graphic aid for interpreting gas chromatograms

A simple semilogarithm plot of elution volumes can be constructed as an aid to identify components that are members of the same homologous series. This technique is especially useful in organoleptic and flavor studies for identifying small peaks in any gas chromatogram. The method is applicable to chromatograms containing 20 or more peaks, which do not have to be completely resolved. Any member of the homologous series within 4 or 5 carbons of the unknown can be used as a standard for identification. The tentative plots also help in examining chromatograms obtained with hydrogen flame or with β ray-type detector equipment where samples are too small for collection and identification by chemical and physical tests.

Development of color in fats stabilized with amino-hexose-reductones

SummaryAmino reductones derived from hexoses were evaluated for color development in heated, oxidizing fat systems. Browning was observed to some extent with all the amino-hexose-reductones. The brown color frequently faded upon long heating of the oils. The density of color increased with reductone concentration and varied markedly among the different amino reductones. Morpholino-hexose-reductone could be used in lard and vegetable oils at concentrations up to 0.01% without introducing visually detectable amounts of color. Heating soybean oil solutions of the amino reductones at 100°C. under vacuum slowly destroyed the reductone but did not cause development of color. Air or oxygen was required for color production. Addition of citric acid along with the reductone reduced the amount of color developed. Reductones in fat systems show similarities in browning to reductones in aqueous systems. New considerations for the mechanism of antioxidation by polyphenols and reductones in oils are presented.