Helen A. Moser

Analyses of lipids and oxidation products by partition chromatography. Dimeric and polymeric products

A liquid-partition chromatographic method was developed to determine dimers in fats. Silicie acid treated with 20% methanol in benzene served as the immobile phase. A mixture of 2% methanol in benzene was the mobile solvent. Chromatographic separation of free fatty acids from oxidized-deodorized oils gave three well-isolated fractions composed of unoxidized acids, dimeric or polymeric fatty acids, and polar fraction (ethyl ether eluate). Recovery of acidic materials from the column was essentially quantitative (96–100%), reproducibility was good, and the standard error of regression was ±0.26.A linear relationship exists between the dimer content of deodorized soybean oil and the peroxide value of the oil before deodorization. An increase of 1% in dimer concentration corresponds to an increase in peroxide value of approximately 40. Dimer content of different vegetable oils varied from 1 to 3%.The chromatographic method can be used to estimate the degree of oxidation that an oil has received before deodorization and to follow various phases of fat oxidation, polymerization, and processing.

Edible oil quality as measured by thermal release of pentane

As part of their thermal decomposition products, fatty hydroperoxides produce normal hydrocarbons. The extent of hydrocarbon formation can be measured and associated with the quality and potential stability of an oil. Edible oils containing linoleic acid develop 13-hydroperoxy-9,11-octadecadienoic acid as one product of autoxidation. On thermal decomposition this hydroperoxide yields pentane; the amount released has been correlated with the flavor scores of fresh and aged soybean and cottonseed oils and with the peroxide values of these oils. The quantity of pentane released has an inverse linear relationship to flavor score and a direct linear relationship to peroxide values. Edible oils exposed to light exhibit a different relationship between flavor score and thermally derived pentane than do the same oils when autoxidized in the dark.

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.

Long term storage of soybean and cottonseed salad oils

Commercially prepared and packaged soybean and cottonseed salad oils from several different processors were evaluated periodically during storage for 12 months. Partially hydrogenated and winterized soybean oils, as well as unhydrogenated soybean salad oils, were stored in bottles and cans at 78 and 100 F. Control samples of all oils were held at 0 F during the entire test. Some lots in bottles and cans were packaged under nitrogen to improve storage stability. Agreement was good between organoleptic and oxidative evaluation of aged oils. After 26 weeks of storage at 100 F, the flavor of partially hydrogenated-winterized oils packaged under nitrogen showed a minimum loss. These same oils did not exhibit much, if any, reduction in their oxidative stability as indicated by storage peroxide values (active oxygen method). Soybean oil not protected with nitrogen demonstrated progressive flavor deterioration at 100 F. After 10 weeks of storage, the deterioration became marked and the flavor score was below 5. From limited observations, bottled oils appear to have a better stability than oils packaged in screw-cap tin cans. Hydrogenated oils packaged under nitrogen in cans had good oxidative stability, but some lowering of the flavor score was observed. Nonhydrogenated soybean oils packaged in tin cans not under nitrogen exhibited the most rapid flavor deterioration of all lots of oil investigated.

Odor and flavor responses to additives in edible oils

The odor threshold was determined for a series of unsaturated ketones, secondary alcohols, hydrocarbons and substituted furans added to bland edible oil. Odor thresholds were taken as the point where 50% of a 15- to 18-member taste panel could detect an odor difference from the control oil. These additives are oxidative products of fats, but the concentrations investigated were far below any level associated with an identifying odor or taste of the additive per se. Odor, rather than flavor, was selected as the starting basis because of greater acuity and ease of handling a large number of samples with less taster fatigue. Oil samples containing additive concentrations near the odor threshold levels were evaluated by flavor score and flavor descriptions. Taste panel members were experienced oil tasters and were allowed free choice in selecting terms to describe the flavor quality of the oil samples. The propyl and butyl members of the homologous series of vinyl ketones had the lowest odor thresholds, whereas the difference in odor threshold was small between homologs in the unsaturated alcohols and in the 2 substituted furans. Vinyl propyl ketone, vinyl propyl carbinol (1-hexen-3-ol) and 2-propyl furan had odor thresholds of 0.005, 0.5 and 6 ppm, respectively. Odor thresholds of the unsaturated hydrocarbons are markedly lower than those of the saturated isologs. The odor of nonane can be detected at 650 ppm. However, at 1000 ppm it cannot be tasted and oils containing it were scored equal to the control oil. 1-Nonene, 1-nonyne and other tested C-9 unsaturated hydrocarbons, including a number of dienes, have odor thresholds of about 10 ppm. The hydrocarbons 1-hexyne, 1-nonyne and 1-decyne had odor thresh-olds of 0.2, 5 and 4 ppm, respectively.

A LIGHT TEST TO MEASURE STABILITY OF EDIBLE OILS.

The effect of light on the flavor of edible oils and of various fat-containing foods is reviewed to show its importance in food studies and the need for a method of evaluation. Such a test, in which fluorescent light is used in an easily assembled unit, has been developed, and the parameters for its use have been determined. Identical samples of soybean oil exposed on 10 different days and organoleptically evaluated show the method to be reproducible with a standard deviation of 0.79 with a scoring system of 1–10. This method was then applied to soybean, cottonseed, safflower and hydrogenated-winterized soybean oils, and a light-exposure value was determined for each oil based on a comparison with accelerated storage procedures ordinarily used. Advantages of this light test over current procedures are the short time required for completion, the reduction of variation by a controlled light source, reproducibility of results and its adaptability to related food products.

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.

Tandem gas chromatography-mass spectrometry analysis of volatiles from soybean oil

A time vs. volatile decomposition study was made on commercially available soybean oil aged under normal laboratory room conditions. Samples were taken at weekly intervals for peroxide value (PV) determinations, organoleptic evaluations and volatile analyses. Volatiles, stripped from the oil samples in an all-glass system devoid of connecting joints, were collected and sealed in attached capillary tubes. The encapsulated compounds were introduced into a tandem gas chromatograph-mass spectrometer via a capillary crusher. All collections, transfers or introductions of volatiles were performed without the aid of solvents. Hydrocarbons and, subsequently, aldehydes were the principle volatiles associated with the initial and intermediate stages of soybean oil autoxidation (PV 0–11). A variety of other compounds were also found as the level of autoxidation increased. Identified compounds, PVs and organoleptic evaluations are correlated.

Amino-hexose-reductones as antioxidants. I. Vegetable oils

SummaryAmino-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.

Flavor evaluation of copper-hydrogenated soybean oils

The use of copper catalyst to reduce selectively the linolenate in soybean oil improves its flavor stability. As previously shown, the copper must be removed or properly inactivated to obtain an oil of high initial quality. In oven and heat tests, odor and flavor development in the hydrogenated soybean oil samples correlate surprisingly well with actual levels of linolenate, but there were some differences in overall responses among cottonseed oil, copper-reduced (0.0% linolenate) and nickel-reduced (3.0% linolenate) soybean oils. The taste panel generally scored the last three oils in the following order: cottonseed oil, copper-reduced and nickel-reduced soybean oil.