Diacetyl as the buttery flavor component in soybean oil

Soybean oil often exhibits a buttery flavor in the early stages of autoxidation. Molecular distiliates from “buttery” soybean oil consisted of aqueous and oily layers. The aqueous layer contained the buttery flavor. During gas chromatography, the buttery flavor compound had a retention time similar to diacetyl on both polar and nonpolar columns. Diacetyl-bis-2,4-dinitrophenyl-hydrazone was isolated from the aqueous layer of the distillate. Diacetyl added to fresh soybean oil faithfully reproduced the buttery flavor. Journal Paper No. J-5107 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa Project No. 1517. Presented at the AOCS Meeting, Houston, April 1965.     

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.     

Frying stability of soybean and canola oils with modified fatty acid compositions

Pilot plant-processed samples of soybean and canola (lowerucic acid rapeseed) oil with fatty acid compositions modified by mutation breeding and/or hydrogenation were evaluated for frying stability. Linolenic acid contents were 6.2% for standard soybean oil, 3.7% for low-linolenic soybean oil and 0.4% for the hydrogenated low-linolenic soybean oil. The linolenic acid contents were 10.1% for standard canola oil, 1.7% for canola modified by breeding and 0.8% and 0.6% for oils modified by breeding and hydrogenation. All modified oils had significantly (P<0.05) less room odor intensity after initial heating tests at 190°C than the standard oils, as judged by a sensory panel. Panelists also judged standard oils to have significantly higher intensities for fishy, burnt, rubbery, smoky and acrid odors than the modified oils. Free fatty acids, polar compounds and foam heights during frying were significantly (P<0.05) less in the low-linolenic soy and canola oils than the corresponding unmodified oils after 5 h of frying. The flavor quality of french-fried potatoes was significantly (P<0.05) better for potatoes fried in modified oils than those fried in standard oils. The potatoes fried in standard canola oil were described by the sensory panel as fishy.     

Frying quality and stability of low-and ultra-low-linolenic acid soybean oils

To determine effects of very low levels of linolenic acid on frying stabilities of soybean oils, tests were conducted with 2% (low) linolenic acid soybean oil (LLSBO) and 0.8% (ultra-low) linolenic acid soybean oil (ULLSBO) in comparison with cottonseed oil (CSO). Potato chips were fried in the oils for a total of 25 h of oil use. No significant differences were found for either total polar compounds or FFA between samples of LLSBO and ULLSBO; however, CSO had significantly higher percentage of polar compounds and FFA than the soybean oils at all sampling times. Flavor evaluations of fresh and aged (1, 3, 5, and 7 wk at 25°C) potato chips showed some differences between potato chips fried in different oil types. Sensory panel judges reported that potato chips fried in ULLSBO and aged for 3 or 7 wk at 25°C had significantly lower intensities of fishy flavor than did potato chips fried in LLSBO with the same conditions. Potato chips fried in ULLSBO that had been used for 5 h and then aged 7 wk at 25°C had significantly better quality than did potato chips fried 5 h in LLSBO and aged under the same conditions. Hexanal was significantly higher in the 5-h LLSBO sample than in potato chips fried 5 h in ULLSBO. The decrease in linolenic acid from 2 to 0.8% in the oils improved flavor quality and oxidative stability of some of the potato chip samples.     

Effect of Pretreatments and Drying Methods on the Properties and Fishy Odor/Flavor of Gelatin from Seabass (Lates calcarifer) skin

Effects of different pretreatments of seabass skin and various drying methods on properties and fishy odor/flavor of resulting gelatin were evaluated. All gelatins contained α- and β-chains as the predominant components. Generally, a higher gel strength was found in the freeze-dried gelatin, compared with spray-dried counterpart (p < 0.05). Gel strength of gelatin decreased as the inlet temperature for spray drying increased (p < 0.05). All gelatin samples had creamy whitish color but became more yellow as the inlet temperature for spray drying increased. All gelatin gels were sponge- or coral-like in structure. Gelatin from skin pretreated with citric acid had lower fishy odor/flavor than that from skin pretreated using acetic acid. The lower fishy odor/flavor with coincidentally lower abundance of volatile compounds, including aldehydes, ketones, and alcohols, etc., was found in gelatin obtained by spray drying, in comparison with its freeze-dried counterpart. The lower fishy odor/flavor in spray-dried gelatin was in accordance with the lower thiobarbituric acid reactive substances and peroxide values. Thus, spray drying in conjunction with an appropriated pretreatment could be an effective method for production of gelatin with negligible undesirable fishy odor and flavor.     

Performance evaluation of hexane-extracted oils from genetically modified soybeans

Soybeans produced by induced mutation breeding and hybridization were cracked, flaked and hexane-extracted, and the recovered crude oils were processed to finished edible oils by laboratory simulations of commercial oil-processing procedures. Three lines yielded oils containing 1.7, 1.9 and 2.5% linolenic acid. These low-linolenic acid oils were evaluated along with oil extracted from the cultivar Hardin, grown at the same time and location, and they were processed at the same time. The oil from Hardin contained 6.5% linolenic acid. Low-linolenic acid oils showed improved flavor stability in accelerated storage tests after 8 d in the dark at 60°C and after 8h at 7500 lux at 30°C, conditions generally considered in stress testing. Room odor testing indicated that the low-linolenic oils showed significantly lower fishy odor after 1 h at 190°C and lower acrid/pungent odor after 5 h. Potatoes were fried in the oils at 190°C after 5, 10 and 15 h of use. Overall flavor quality of the potatoes fried in the low-linolenic oils was good and significantly better after all time periods than that of potatoes fried in the standard oil. No fishy flavors were perceived with potatoes fried in the low-linolenic oils. Total volatile and polar compound content of all heated oils increased with frying hours, with no significant differences observed. After 15 h of frying, the free fatty acid content in all oils remained below 0.3%. Lowering the linolenic acid content of soybean oil by breeding was particularly beneficial for improved oil quality during cooking and frying. Flavor quality of fried foods was enhanced with these low-linolenic acid oils.     

Volatile compounds produced during deodorization of soybean oil and their flavor significance

Freshly deodorized soybean oil has a characteristic nutty flavor but often yields no detectable headspace volatiles. The cause of this flavor was investigated by deodorizing soybean oil in an apparatus with a double cold trap that allowed the volatile compounds formed from the initial decomposition of hydroperoxides to be collected separately from those produced during the normal deodorization process. The chief volatile components from the normal deodorization process were hydrocarbons, which contributed little to no odor to the oil. The compounds with the greatest odor were carbonyls, especially heptanal and cis-4-heptenal. Although these components should accumulate at some steady-state concentration in an oil during its deodorization, none seemed to account for the flavor of the deodorized oil. By using a particle detector, it was shown that small particles could be generated in the human mouth that could provide a mechanism to bring oil with nonvolatile flavor components into contact with the olfactory organ. Attempts to separate possible nonvolatile flavors in deodorized oil from triacylglycerides by chromatography on alumina or reaction with 2,4-dinitrophenylhydrazine were unsuccessful. Possibly, the flavor is caused by the glycerol esters themselves.     

Volatile compounds produced during deodorization of soybean oil and their flavor significance

Freshly deodorized soybean oil has a characteristic nutty flavor but often yields no detectable headspace volatiles. The cause of this flavor was investigated by deodorizing soybean oil in an apparatus with a double cold trap that allowed the volatile compounds formed from the initial decomposition of hydroperoxides to be collected separately from those produced during the normal deodorization process. The chief volatile components from the normal deodorization process were hydrocarbons, which contributed little to no odor to the oil. The compounds with the greatest odor were carbonyls, especially heptanal and cis-4-heptenal. Although these comonpents should accumulate at some steady-state concentration in an oil during its deodorization, none seemed to account for the flavor of the deodorized oil. By using a particle detector, it was shown that small particles could be generated in the human mouth that could provide a mechanism to bring oil with nonvolatile flavor components into contact with the olfactory organ. Attempts to separate possible nonvolatile flavors in deodorized oil from triacylglycerides by chromatography on alumina or reaction with 2,4-dinitrophenylhydrazine were unsuccessful. Possibly, the flavor is caused by the glycerol esters themselves.     

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.     

Identification of volatile flavor compounds developed during storage of a deodorized hydrogenated soybean oil

Hydrogenated soybean oil, even after it has been thoroughly deodorized, will develop a characteristic, objectionable flavor known as hydrogenation flavor during storage. The volatile compounds in such an oil were isolated, fractionated by gas chromatography, and the gas chromatographic fractions identified by IR and mass spectrometry. A total of 48 compounds was identified. Among them, 2-trans-6-trans-octadienal, and higher alcohols and lactones, appeared to play an important role in contributing to the hydrogenation flavor.     

Effects of thermally oxidized triglycerides on the oxidative stability of soybean oil

Soybean oil purified by silicic acid column chromatography did not contain peroxides, free fatty acids, phospholipids or oxidized polar compounds. The purified soybean oil was thermally oxidized at 180°C for 96 hr in the presence of air. The thermally oxidized compounds (31.3%) were separated from the purified soybean oil by gradient elution silicic acid chromatography. Thermally oxidized compounds contained hydroxyl groups, carbonyl groups andtrans double bonds according to the infrared spectrum. Thermally oxidized compounds were added to soybean oil and purified soybean oil at 0, 0.5, 1.0, 1.5 and 2.0% to study the effects of these compounds on the oxidative stability of oil. The oxidative stabilities of oils were determined by gas chromatographic analysis of volatile compound formation and molecular oxygen disappearance in the headspace of oil bottles. The thermally oxidized compounds showed prooxidant effects on the oxidative stabilities of both refined, bleached and deodorized soybean oil and purified soybean oil. Duncan’s Multiple Range Test showed that thermally oxidized compounds had a significant effect on the volatile compound formatiion and oxygen disappearance in the headspace of oil at α=0.05.     

The flavor intensity of some carbonyl compounds important in oxidized fats

The flavor intensities of several methyl ketones, aldehydes, 2-enals, andtrans, trans-2,4-dienals were evaluated in 1% mineral oil in water emulsions against a series of standard emulsions of 2-heptanone. There was a linear relation between the logarithm of the concentrations of the carbonyls and the logarithm of the concentration of 2-heptanone giving an equal flavor intensity. Thresholds calculated from these linear relations were comparable to those reported in the literature. Mixtures of carbonyls similar to those found in oxidized soybean oil were evaluated, and their flavor intensities were similar to those predicted from adding the intensities of the individual carbonyls. The flavor intensity of these carbonyls could account for the flavor intensity of oxidized soybean oil.     

Use of labeled compounds to study the mechanism of flavor formation in oxidizing fats

2-¹⁴C-Hexanal,trans, trans-5-¹⁴C-2,4-decadienal, 4-¹⁴C-1-octen-3-ol, 4-¹⁴C-1-octen-3-one and 1-¹⁴C-1-pentanol were synthesized and added to freshly deodorized soybean oil in concentrations ranging from 7–125 ppm. The soybean oil was oxidized, and the fate of the labeled compounds was followed. Hexanal was converted to hexanoic acid especially at 50 C or higher. The 2,4-decadienal was converted to 2,4-decadienoic acid at room temperature, and heptenal, 2-octanal, 2-nonanal, glyoxal and malonaldehyde were found among the labeled products. 1-Octen-3-ol was converted to 1-octen-3-one at room temperature, but the 1-octen-3-one formed a stable end product that produced no other labeled compounds. 1-Pentanol was converted to pentanoic acid at 50 C or higher. One of 13 papers presented in the symposium “Flavor Research in Fats and Fat Bearing Foods,” AOCS Meeting, Atlantic City, October 1971. Journal Paper No. J-7082 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50010. Project 1856.     

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 new technique for the isolation of flavor components from fats and oils

A new continuous process for the isolation of flavor compounds from fats and oils has been developed. This new technique involves 1) countercurrent contact of the oil with steam in a 30 plate Oldershaw column, 2) condensation of the steam carrying the flavor compounds in a trap cooled with liquid nitrogen, 3) continuous liquid-liquid extraction of the condensate with a small amount of ethyl ether, and 4) removal of the solvent with a 6 plate Oldershaw column. In this process the oil is heated to 80°C. for only 12 min. The peroxide number of a reverted soybean oil only decreased from 4.1 to 3.4 meq./kg. by this treatment. Flavor compounds isolated from an oil by this new technique are characteristic of the oil. Very little decomposition occurs during the isolation process and therefore the flavor compounds isolated represent truly the flavor orginally present in the oil. Flavor compounds isolated from a reverted-but-not-rancid soybean oil when added to a bland coconut oil at a concentration of less than 10 ppm make it taste exactly like a reverted soybean oil.     

Isolation and identification of 2-pentenylfurans in the reversion flavor of soybean oil

The volatile flavor compounds in a reverted soybean oil with a peroxide number of 6.0 meq/kg were isolated by semicontinuous countercurrent vacuum steam distillation. Based upon the gas Chromatographic retention times and mass spectra of the four synthesized 2-pentenylfurans, it was found that cis- and trans-2-(l-pentenyl)furans and a mixture of cis- and trans-2-(2-pentenyl)-furans are present in reverted soybean oil. At least the greater portion of 2-(2-pentenyl)furans identified was cis-isomer. These compounds may contribute to the reversion flavor of soybean oil. Presented at the 73rd AOCS annual meeting, Toronto, 1982.     

A systematic characterization of the reversion flavor of soybean oil

The volatile flavor compounds in a reverted soybean oil with a peroxide number of 4.3 meq/kg were isolated by a semicontinuous counter-current vacuum steam-distillation process, fractionated by repeated gas chromatography, and identified by infrared and mass spectrometry. A total of 71 compounds were identified, which included 19 acids, 39 nonacidic compounds, and 13 tentatively identified compounds. The acids consisted of eight normal saturated acids, nine α,β-unsaturated acids, a branch-chain acid, one hydroxy acid, two keto acids, three lactones, and one aromatic acid. The nonacidic compounds consisted of two esters, eight normal saturated aldehydes, two branched-chain aldehydes, five 2-enals, three dienals, eight ketones, eight alcohols, six hydrocarbons, and four aromatic compounds. The mechanism of formation of the identified compounds indicated that they were mostly primary or secondary autoxidation products of the hydroperoxides of the unsaturated fatty esters. Since many of the identified compounds were produced from oleic and linoleic acids, it is doubtful that linolenic acid was solely responsible for the reversion flavor. Of the compounds identified two are of unusual interest. They are 1-decyne and 2-pentyl furan. The former is the first acetylenic compound reported as the autoxidation products of unsaturated fatty esters which contained only double bonds. The latter imparts to an oil at concentrations of 5–10 ppm a beany and grassy flavor reminiscent of that of a reverted soybean oil. Since this compound is postulated as being produced by the autoxidation of linolenic acid, it is suggested that the presence of linolenic acid catalyzes the autoxidation of linoleic acid and possibly alters the decomposition pattern of its hydroperoxides.     

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 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.