A. W. Schwab

The flavor problem of soybean oil. IV. Structure of compounds counteracting the effect of prooxidant metals

SummaryA study has been made of the effectiveness of various polycarboxylic acids and polyhydric alcohols in improving the stability of soybean oil. Certain observations have been made regarding the structural groups required and the possible mechanism of reaction. Since salts and esters of organic acids are inactive, free carboxyl groups are required. Among the four carbon atom dicarboxylic acids activity increases with the number of hydroxyl groups. Within the polyalcohols activity increases with the increase in number of hydroxyl groups. Steric immobility and loss of hydroxyl groups by dehydration reduces activity. Evidence is presented which attributes to citric acid and certain polyhydric alcohols the role of metal scavenger. For example, it has been demonstrated that the addition of citric acid and sorbitol to soybean oil containing prooxidant metallic salts effectively increases the oxidative and flavor stability of the oil. By using a sample of treated soybean oil with no detectable tocopherols, in order to eliminate synergistic effects of citric acid, it has been shown that the prooxidant effect of iron stearate is counteracted by the presence of citric acid. The demonstration that polyhydric alcohols increase the flavor and oxidative stability is compatible with their known metal complexing properties. Evidence is presented which indicates a relationship between flavor stability and oxidative stability.

The flavor problem of soybean oil. III. A four-sample, glass laboratory deodorizer

SummaryA glass laboratory deodorizer has been described which permits the simultaneous deodorization of four samples under nearly identical conditions of time, temperature, pressure and rate of steam flow. The design includes provision for measuring and controlling the steam flow, for preventing bumping, for “breaking” the vacuum, and for heating and cooling the deodorizer. Successful deodorizations have been made in relatively short periods of time. Upon deodorization of the same alkali-refined bleached oil in each of the four flasks no difference has been found either in the initial quality or in the stability of the samples.

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.

The flavor problem of soybean oil. V. Some considerations in the use of metal scavengers in commercial operations

SummaryCitric acid and sorbitol were tested on a commercial scale and their use was found to improve the oxidative and flavor stability of soybean oil.The optimal concentration for the addition of citric acid and sorbitol is of the order of 0.01%, 0.001% being insufficient, and 0.1% giving no significant increase in flavor stability over 0.01%.Heating is not necessary for the activation of citric acid; however, it is advantageous to add the citric acid at the beginning of the deodorization in commercial operations because of the protection imparted to the oils during deodorization. Since citric acid is destroyed during deodorization, it appears desirable, on the basis of laboratory experiments, to introduce additional citric acid during the cooling phase of deodorization.Phosphatides added to the deodorizer increase the oxidative and flavor stability of soybean oil and counteract the pro-oxidant effect of added iron. Phosphatides are thus considered to comprise a fat-soluble form of phosphoric acid and to perform the function of a metal scavenger. The value of the second degumming step of the German process is dubious. In neither the laboratory experiments nor in a commercial run were the differences due to this operation found to be significant.

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.

Free radical addition of hydrogen sulfide and thiols to linseed oil and methyl oleate

Free radical additions of hydrogen sulfide, ethanedithiol, and 1,6-hexanedithiol have been made to methyl oleate and linseed oil with ultraviolet radiation. Reactions were carried out in dichloromethane at −70C and in benzene at 25C. With the dithiols, a new dibasic ester has been prepared from methyl oleate in which bridging is accomplished through a dithiol moiety. Hydrogen sulfide has been added to linseed oil in suitable solvents at both −70C and 25C. It appears that zero-order kinetics control the additions at both temperatures. Infrared data show a linear relationship between mercapto absorption and the amount of sulfur incorporated. Nuclear magnetic resonance (NMR) spectra demonstrate a decrease in olefinic protons with an increase in sulfur content. Fair agreement on the extent of reaction exists between data from NMR, sulfur content, and infrared analyses. Hydrogen sulfide-treated linseed oil films air-dry slowly at room temperature; at 250C for 1 hr under a CO2 atmosphere these oils cure to brown films with Sward Rocker values of 24 to 32 and pencil hardness values of five to greater than six. Pencil hardness and alkali resistance increased with sulfur content. The film from the 4.2% sulfur sample resisted alkali at room temperature for 24 hr.

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.

Alkyd resins modified with cyclic fatty acids a preliminary evaluation

Alkyd resins were modified to 50% oil length with crude, flash-distilled, and 78% pure cyclic fatty acids. These resins were compared with ones modified with naturally occurring fatty acids and with vegetable oils. Those modified with the cyclic acids process more rapidly than those prepared with linseed, safflower, or soybean fatty acids, and they also have good nonyellowing properties. Resins modified with 78% pure cyclic acids show definite improvement in drying time, hardness, and chemical resistance in air-dried films, and an almost equal improvement in baked films, over resins obtained with the other modifiers. Distilled cyclic acids also improve alkyd resins although not to the extent that pure acids do. Both give resins superior to commercial oil-modified resins under the test conditions. Resins with crude cyclic acids are as good in air-dried films as are the others, but are poorer in baked films.

Nucleophilic and radical addition of H2S to methyl linolenate and linseed oil

Hydrogen sulfide was added to methyl linolenate and linseed oil to yield mercapto, thio, and thiolan derivatives. Nucleophilic conditions at low temperatures gave faster and more complete reactions than did free radical conditions. Major reaction products were identified by gas liquid chromatography, mass spectrometry, and nuclear magnetic resonance. Nucleophilic addition of hydrogen sulfide to the methyl esters of hydrogenated nonconjugatable linseed oil was made at −70 C in the presence of boron trifluoride, and thiolan derivatives appeared to form in preference to thiane derivatives.