Some carbonyl flavor compounds of oxidized soybean and linseed oils

Evidence is presented that 2,3-pentanedione, as well as diacetyl, contributes to the buttery flavor found in the early stages of oxidation of soybean oil. Components with a fishy and potatoey flavor were found in distillates from soybean oil that had a fishy or paint-like flavor. Linseed oil proved a reliable source of these flavor compounds. The fishy compound was identified ascis-4-heptenal and the potatoey compound is probably 2,4-pentadienal. Mechanisms for the production of these compounds are suggested. Journal Paper No. J-6183 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, Project No. 1517.     

Studies on the flavor of autoxidized soybean oil

The flavor components of soybean oil in the early stages of autoxidation were isolated by distillation in a molecular still. The distillate consisted of an aqueous layer and an oily film. The oily film did not reproduce the autoxidized flavor when added to freshly deodorized oil. Gas chromatographic and organoleptic analysis indicated that the oily film contained hexanal, vinylamyl ketone, andtrans,cis-2,6-nonadienal. The aqueous layer reproduced the autoxidized flavor when added to freshly deodorized oil, and the flavor had a retention time on butandiol succinate columns between those of pentanal and hexanal. Mixtures of vinylethyl ketone and pentanal gave a flavor to freshly deodorized oil similar to the flavor of oil in the early stages of autoxidation. Vinylethyl ketone was identified in the distillate from autoxidized soybean oil as the 2,4-dinitrophenylhydrazone. Presented at the AOCS Meeting, Minneapolis, 1963.     

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. One of 10 papers to be published from the Symposium “Hydrogenation”. presented at the AOCS Meeting, New Orleans, April 1970. No. Utiliz. Res. Dev. Div., ARS, USDA.     

Oxidative stability of soybean oils with altered fatty acid compositions

The oxidative stabilities of one canola oil and six soybean oils of various fatty acid compositions were compared in terms of peroxide values, conjugated dienoic acid values and sensory evaluations. Two of the soybean oils (Hardin and BSR 101) were from common commercial varieties. The other four soybean oils were from experimental lines developed in a mutation breeding program at Iowa State University that included A17 with 1.5% linolenate and 15.2% palmitate; A16 with 2% linolenate and 10.8% palmitate; A87-191039 with 2% linolenate and 29.6% oleate; and A6 with 27.5% stearate. Seed from the soybean genotypes was cold pressed. Crude canola oil was obtained without additives. All oils were refined, bleached and deodorized under laboratory conditions with no additives and stored at 60°C for 15 days. The A17, A16, A87-191039 and A6 oils were generally more stable to oxidation than the commercial soybean varieties and canola oil as evaluated by chemical and sensory tests. Canola oil was much less stable than Hardin and BSR 101 oils by both chemical and sensory tests. The peroxide values and flavor scores of oils were highly correlated with the initial amounts of linolenate (r=0.95, P=0.001). Flavor quality and flavor intensity had negative correlations with linolenate, (r=−0.89, P=0.007) and (r=−0.86, P=0.013), respectively.     

Analysis of furanoid esters in soybean oil and the effect of variety and environment on furanoid ester content

An improved method was developed to analyze the major furanoid esters in soybean oil. The method is based on urea fractionation of the methyl esters, silver ion chromatography, and gas chromatography of the furanoid concentrate. Activation of the soybean lipoxygenase decreased the amount of furanoid ester recovered from the oil, but the degumming of crude soybean oil and the choice of solvent used to extract soybean lipids caused no change in furanoid ester content. Fifty-six soybean varieties, representing a wide range in maturity group and geographical origin, were grown in Puerto Rico and used to determine the range of furanoid ester contents. Furanoid ester II ranged from 0.033–0.29 mg/g, and ester III ranged from 0.058–0.27 mg/g. The two major furanoid esters were positively correlated with each other and with maturity group. Growth environment as well as variety caused significant differences in furanoid content. Journal Paper No.J-17180 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA, 50011, Project No. 3414.     

A review of soybean oil reversion flavor

Crude soybean oil has a characteristic “greenbeany” flavor, which during refining, bleaching and deodorization is eliminated to produce a bland tasting, light colored oil. However, flavor returns during storage and has been characteristically called the “reversion flavor” of soybean oil. This deleterious characteristics flavor has influenced the utilization of soybean oil and its fatty acids. Several theories for the cause of reversion flavor include: (a) oxidation of linolenic acid; (b) oxidation of isolinoleic acid of the 9,15-diene structure; (c) phosphatide reactions; (d) unsaponifiables; and (e) oxidative polymers. References are presented that support or contradict these theories. Recent publications concerning the isolation and characterization of the components of reversion flavor indicate slight oxidation of the fatty acids is the major cause. Techniques that are effective in increasing the flavor stability of soybean oil are presented.     

The impact of furanoid fatty acids and 3-methylnonane-2,4-dione on the flavor of oxidized soybean oil

Oils from soybeans with high or low contents of furanoid fatty acids were evaluated during storage for flavor intensity of soybean oil (SBO) off-flavor, but no significant differences were found. In addition, the compound 3-methylnonane-2,4-dione (MND), a breakdown product of furanoid fatty acids suggested by other researchers to contribute to reversion flavor of SBO, was evaluated for its contribution to off-flavor. The compound was synthesized in the laboratory and purified by gas chromatography (GC) on a Silar 10 C column. GC analysis of the purified MND on a nonpolar SPB-1 column showed two well-separated main peaks that have been suggested to represent keto and enol forms. Between these two peaks, a bridge of poorly resolved compounds may have represented various possible enol forms or an equilibration among these forms during the GC separation. MND had an intense straw-like and frulty odor when evaluated at the outlet of a gas chromatograph. Sensory evaluation of MND in a mineral oil/water emulsion system showed that its flavor intensity increased almost imperceptibly with increased concentration (from 0.09 to 2.56 ppm). An explanation for this unusual flavor response may be that, when molecularly dispersed in air, MND has an intense odor, but when placed in a mineral oil or soybean oil emulsion, MND may exist in a form with relatively low flavor intensity, or it may be bound by the media. The concentrations of MND in SBO at various peroxide values were measured at 0 to 0.804 ppb, which were far less than concentrations tested in mineral oil/water emulsions during sensory evaluation and below published odor threshold values for MND in oil. Therefore, these results do not support the theory that furanoid fatty acids or MND contribute strongly to the reversion flavor of SBO. This is Journal Paper J.17472 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 3396.     

Flavor and oxidative stability of some linolenate-containing oils

Because crambe, mustard seed, and rapeseed oils, like soybean oil, contain linolenate ester, they have been examined and compared with soybean oil for flavor stability after accelerated storage and after exposure to fluorescent light. Tests showed that the Cruciferae oils did have similar flavor characteristics and that the addition of citric acid did improve their stability. When exposed to light, the citric acid-treated Cruciferae oils differed from soybean oil; they developed a rubbery flavor, whereas soybean oil developed a grassy flavor. Oxidative stability determined by the active oxygen method confirmed results of oven storage tests. This work supports the belief that if linolenic acid is present in an edible oil, it is a precursor to typical off-flavor development. Presented at the AOCS meeting, Chicago, 1964. A laboratory of the No. Utiliz, Res. and Dev. Div., ARS, USDA.     

Flavor score correlation with pentanal and hexanal contents of vegetable oil

Samples of commercially processed soybean, cottonseed, and peanut oils were stored under controlled conditions then evaluated for flavor by a 20-member trained, experienced oil panel and for pentanal and hexanal contents by direct gas chromatography. The oils, which contained citric acid and/or antioxidants, were either aged from 0 to 16 days at 60 C or exposed to fluorescent light for 0 to 16 hr. The simple linear regressions of flavor score with the logarithm of pentanal or hexanal content in aged soybean oil gave correlation coefficients of −0.96 and −0.90, respectively; for cottonseed oil, −0.60 and −0.85; and for peanut oil −0.74 and −0.75. Addition of peroxide values to the linear regressions increased the correlation coefficients. Flavor scores of cottonseed and peanut oil can be predicted from pentanal and hexanal contents, but the technique is slightly more reliable for soybean oil based on the treatments used for these oils. Presented at the AOCS Meeting, Chicago, September 1973.     

Flavor and oxidative stability of soybean,sunflower and low erucic acid rapeseed oils

Three samples each of soybean, sunflower and low erucic acid rapeseed (LEAR) oils were evaluated for flavor and oxidative stability. The commercially refined and bleached oils were deodorized under identical conditions. No significant differences were noted in initial flavor quality. After storage at 25°C or 60°C in the dark, soybean oils—with or without citric acid—were more stable than either sunflower or LEAR oils. However, in the presence of citric acid, soybean oils were significantly less stable to light exposure than either LEAR or sunflower oils. In contrast, in the absence of citric acid, soybean oils were significantly more light stable than LEAR oils. In either the presence or absence of citric acid, sunflower oil was significantly more stable to light than soybean oil. Analyses by static headspace gas chromatography showed no significant differences in formation of total volatile compounds between soybean and LEAR oils. However, both oils developed significantly less total volatiles than the sunflower oils. Each oil type varied in flavor and oxidative stability depending on the oxidation method (light vs dark storage, absence vs presence of citric acid, 100°C vs 60°C). Presented at the annual meeting of the Canadian Section of AOCS, held in October 1987 in Winnipeg, Manitoba, Canada.     

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

Summary Oxidation 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. Presented at fall meeting, American Oil Chemists’ Society, October 20–22, 1958, Chicago, Ill. This is a laboratory of the Northern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture.     

A sensitive method for the determination of carbonyl compounds

2,4,6-Trichlorophenylhydrazine was tested as a reagent for carbonyl compounds. As little as 0.1 of the 2,4,6-trichlorophenylhydrazones (2,4,6-TCPH) could be measured with an electron capture detector, so this reagent should be useful in measuring the carbonyl compounds in oxidized fats at levels near their flavor thresholds. Mixtures of 2,4,6-TCPHs were separated by thin layer chromatography. Alkan-2-one-2,4,6-TCPHs were separated from aldehyde-2,4,6-TCPHs on alumina plates. The alkanal, alk-2-enal and alk-2,4-dienal-2,4,6-TCPHs were separated from each other either on silica gel plates or silica gel-silver ion plates. The derivatives within each carbonyl class were separated by chain length on chromatography media impregnated with phenoxyethanol. The 2,4,6-TCPHs eluted from thin layer plates were determined with an electron capture detector after gas chromatography on a 30 cm column of freeze-dried detergent base coated with a silicone oil. Journal Paper No. J-6842 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, project No. 1856.     

Destabilization of the Emulsion Formed during Aqueous Extraction of Soybean Oil

Characterization and destabilization of the emulsion formed during aqueous extraction of oil from soybean flour were investigated. This emulsion was collected as a cream layer and was subjected to various single and combined treatments, including thermal treatments and enzymatic treatments, aimed at recovery of free oil. The soybean oil emulsion formed during the aqueous extraction processing of full fat flour contains high molecular weight glycinin and β-conglycinin proteins and smaller oleosin proteins, which form a multilayer interface. Heat treatment alone did not modify the free oil recovery but freeze–thaw treatment increased the oil yield from 3 to 22%. After enzymatic treatment of the emulsion, its mean droplet size changed from 5 to 14 μm and the oil recovery increased to 23%. This increase could be attributed to the removal (due to enzymatic hydrolysis) of large molecular weight polypeptides from the emulsion interface, resulting in partial emulsion destabilization. When enzymatic treatment was followed by a freeze–thaw step, the oil recovery increased to 46%. This result can be attributed to the thinner interfacial membrane after enzymatic hydrolysis, partial coalescence during freeze–thaw, and coalescence during centrifugation. Despite the reduction in emulsion stability achieved, additional demulsification approaches need to be pursued to obtain an acceptably high conversion to free oil.     

Determination of the extent of rancidity of soybean oil by gas chromatography compared with peroxide value

The development of rancidity in soybean oil has been studied by gas chromatography (GC), peroxide value (PV) and sensory evaluation. The GC method has been adapted from previous methodology and another type of column packing has been used for the purpose. The GC peaks have been treated as one whole group, and and oxidation value (OV) has been computed by means of an internal standard (n-octanol). The OV’ have been correlated with the PV’s. The flavor of soybean oil and a blend of 50% soybean oil and 50% hydrogenated soybean oil, both kept at 60 C for varying lengths of time, was evaluated by a panel and the results have been presented in a new graphical form. A relationship between the OV and the flavor of the fat has been demonstrated. The merits of the method are discussed.     

Oat Oil: Refining and stability

Oil obtained by petroleum ether extraction of Dal oats was refined by conventional methods. Degumming loss was reduced to 15% by degumming in hexane solution and partially neutralizing the oil with sodium hydroxide. The free fatty acid was 6~8%, and alkali refining losses were 25~30%. Oat oil was bleached successfully with charcoal and deodorized. Stability of the refined oil was compared with soybean oil at 25 and 55 C by peroxide values and organoleptic tests. Stability of oat oil was increased by the addition of citric acid and was significantly greater than that of soybean oil, especially at 25 C. Oat oil contained significant amounts of α-tocopherol, but ferulic and caffeic acids, antioxidants important in whole oats, were not extracted by hexane. Paper No. J-8657 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA, Project No. 2143.     

Improving the fatty acid composition of soybean oil

Efforts to improve the composition of soybean oil by breeding the beans for low linolenic acid in the oil have continued since 1968. This paper reports recent work using hybrid crosses and induced mutations. No lines are yet available that contain oil having less than 3% linolenic acid. Journal Paper No. J-11466 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, Project No. 2475.     

High-temperature stability of soybean oils with altered fatty acid compositions

One canola oil and six soybean oils with different fatty acid compositions were heated intermittently, and bread cubes were fried in them to determine the stability of the oils. Two of the soybean oils were commercial varieties Hardin and BSR 101. The other soybean oils were from experimental lines developed at Iowa State University, and included A17 with 1.5% linolenate (18:3) and 15.1% palmitate (16:0), A16 with 1.9% 18:3 and 10.6% 16:0, A87-191039 with 1.8% 18:3 and 29.1% oleate (18:1) and A6 with 27.7% stearate (18:0). The soybean seeds were cold-pressed and crude canola oil was obtained without additives. Oils were refined, bleached and deodorized under laboratory conditions with additions. Each oil (300 mL) was heated to 180 ± 5°C in a minifryer. Bread cubes were fried at the beginning of heating, and half of the cubes were used for analyses. The second half was analyzed after storage at 60°C for seven days. Heating of the oils was continued for 20 h, cooled for 10 h, and then reheated for another 20 h, after which additional bread cubes were fried and analyzed. Results of sensory evaluation of the fried cubes, the peroxide values (PV) of oils extracted from the cubes and the conjugated dienoic acid values of the oils showed that the A17, A16, A87-191039 and A6 oils had better stabilities than did Hardin, BSR 101 and canola oils. The initial 18:3 contents of oils predicted their oxidative and flavor stabilities under heating and frying conditions (for PVvs. 18:3, r=0.89,P=0.008; for flavor qualityvs. 18:3, r=−0.93,P=0.002; for flavor intensityvs. 18:3, r=−0.91,P=0.004).     

The synthesis of 2-(1-Pentenyl) furan and its relationship to the reversion flavor of soybean oil

Cis and trans-2-(1-pentenyl) furan were postulated as possible contributors to the reversion flavor of soybean oil. These compounds were synthesized, and structures were confirmed by infrared, nuclear magnetic resonance, and mass spectroscopy. Organoleptic evaluation of them in oil suggested that they could contribute to the beany and grassy note of the reverted soybean oil. This approach to flavor problems of food was given a new name — reverse phase flavor chemistry. Paper of the Journal Series, New Jersey Agricultural Experiment Station, Cook College, Rutgers, The State University.     

Soybean oil in dried egg mixes

Dried egg mixes prepared commercially with hydrogenated-winterized soybean, corn, or cottonseed oils were evaluated for initial flavor and for flavor storage stability. Quality evaluations were made on products from two processing plants; flavor, color, stability, and mix volumes were determined periodically during storage at 100 F for 1 year. All mixes contained 15% of the specified oil and were air-packaged in 6 oz laminated foil pouches. Replicated triangle flavor tests on reconstituted dried eggs (scrambled) indicated that neither an analytical-type taste panel nor a palatability panel could distinguish between the mixes containing the different vegetable oils. All samples, regardless of oil component, deteriorated at ca. the same rate when stored at elevated temperatures. Minor differences in flavor scores, color indices, and mix volumes were noted in samples stored at 100 F for 9 or 12 months. A dried egg mix made with hydrogenated-winterized soybean oil could not be distiguished, after 4 months’ aging at 100 F, from a fresh (unaged) mix made with corn oil. After 6 months’ storage at 100 F all aged mixes, regardless of the vegetable oil used in their preparation, could be distinguished from the fresh corn oil mix. Presented at AOCS Meeting, Mexico City, April 1974.