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.     

Rapid analysis of vegetable oil flavor quality by dynamic headspace capillary gas chromatography

A rapid capillary gas Chromatographic headspace technique using a multiple purge and trap system was developed and applied for the determination of vegetable oil flavor quality. Oil volatiles were purged at 150°C for 20 min, collected over a Tenax trap and subsequently desorbed and reconcentrated in a series of two smaller traps. From the gas Chromatographic profile, three compounds, t-2-heptenal, t-2-octenal and t,t-2, 4-decadienal were selected for computation of the flavor score of individual oil samples. Analysis of the flavor quality of soybean oil by this technique demonstrated a very good correlation to the traditional sensory evaluation procedure. Good correlation was also observed for the flavor evaluation of corn oils. Precision, based on multiple analyses of known standard aldehydes, was shown to be better than 6%. The degree of Chromatographic efficiency obtained by this multiple concentration technique permitted the use of a short 25-min Chromatographic run in the resolution of these aldehydes of interest. This approach reduced the overall analysis time of existing instrumental oil flavor techniques significantly.     

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.     

Frying quality and oxidative stability of high-oleic corn oils

To determine the frying stability of corn oils that are genetically modified to contain 65% oleic acid, high-oleic corn oil was evaluated in room odor tests and by total polar compound analysis. Flavor characteristics of french-fried potatoes, prepared in the oil, were also evaluated by trained analytical sensory panelists. In comparison to normal corn oil, hydrogenated corn oil and high-oleic (80 and 90%) sunflower oils, high-oleic corn oil had significantly (P<0.05) lower total polar compound levels after 20 h of oil heating and frying at 190°C than the other oils. Fried-food flavor intensity was significantly higher in the normal corn oil during the early portion of the frying schedule than in any of the high-oleic or hydrogenated oils; however, after 17.5 h of frying, the potatoes fried in normal corn oil had the lowest intensity of fried-food flavor. Corn oil also had the highest intensities of off-odors, including acrid and burnt, in room odor tests. High-oleic corn oil also was evaluated as a salad oil for flavor characteristics and oxidative stability. Results showed that dry-milled high-oleic corn oil had good initial flavor quality and was significantly (P<0.05) more stable than dry-milled normal corn oil after oven storage tests at 60°C, as evaluated by flavor scores and peroxide values. Although the high-oleic corn oil had significantly (P<0.05) better flavor and oxidative stability than corn oil after aging at 60°C, even more pronounced effects were found in high-temperature frying tests, suggesting the advantages of high-oleic corn oil compared to normal or hydrogenated corn oils.     

Effect of altered fatty acid composition on soybean oil stability

During the last 15 years, hybridization and induced mutation breeding of soybeans have been successful in producing an altered fatty acid composition in the extracted oil. The objective of those investigations was to produce a low-linolenic acid soybena oil. Crude oils extracted from the seeds of three such genotypes were processed in laboratory simulations of commercial procedures to finished deodorized oils. Analysis of the fatty acid composition of the three oils showed the linolenic acid content to be 3.3%, 4.2% and 4.8%. The stability of these finished oils was compared to that of oil from a soybean variety having a linolenic acid content of 7.7% and of a commercial hydrogenated-winterized soybean oil (3.0% linolenic acid). Test and control oils were evaluated by a trained sensory panel initially, after accelerated storage at 60 C and during use at 190 C in room tests. Peroxide values were determined at the time of sensory evaluation. Results indicated there was no significant difference in flavor stability during storage between test and control oils. There was no significant difference, between the oils, in peroxide development during accelerated storage. Compared to control oils, the test oils had improved overall room odor intensity scores and lacked the fishy odors of non-hydrogenated soybean oil and the hydrogenated odors of commercial cooking oil. Presented at the AOCS meeting in Honolulu, HI in May 1986.     

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.     

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.     

Flavor and oxidative stability of hydrogenated and unhydrogenated soybean oil: Effect of tertiary butyl hydroquinone

The efficacy of tertiary butyl hydroquinone (TBHQ) treatment for enhancement of the storage stability of soybean oil has been studied by flavor evaluation and chemical analysis. Soybean oils (I) unhydrogenated (IV=137.7; % linolenate=8.3), (II) hydrogenated with nickel catalyst (IV=109.1; % linolenate=3.3), and (III) hydrogenated with copper-chromium catalyst (IV=112.8, % linolenate=0.4) were each deodorized. In the cooling stage of the deodorizer, each oil was treated with citric acid plus TBHQ. These freshly deodorized oils were compared to separate batches of each oil treated with citric acid alone or with citric acid plus butylated hydroxyanisole and butylated hydroxytoluene. An analytical taste panel performed sensory evaluations by a paired sample test using an intensity rating scale system. The oils were also evaluated after being subjected to accelerated storage tests (4 days and 8 days at 60 C) and a fluorescent light exposure test (4 hr, ambient temperature). Peroxide development during storage was beneficially reduced in oils treated with TBHQ. The flavor stability of the three oils was not enhanced by treatment with TBHQ under any test conditions. Presented at ISF-AOCS Meeting, New York, NY, April 27–May 1, 1980.     

AOCS collaborative study on sensory and volatile compound analyses of vegetable oils

An AOCS collaborative study was conducted to determine the effectiveness of sensory analysis and gas chromatographic analyses of volatile compounds in measuring vegetable oils for levels of oxidation that ranged from none to high. Sixteen laboratories from industry, government, and academia in Canada and the United States participated in the study to evaluate the flavor quality and oxidative stability of aged soybean, corn, sunflower, and canola (low-erucic acid rapeseed) oils. Analytical methods included sensory analyses with both flavor intensity and flavor quality scales and gas-chromatographic volatiles by direct injection, static headspace, and dynamic headspace (purge and trap) techniques. Sensory and volatile compound data were used to rank each of the oils at four levels of oxidation—none, low, moderate, and high. For soybean, canola, and sunflower oils, 85–90% of laboratories correctly ranked the oils by either analysis. For corn oil, only 60% of the laboratories ranked the samples according to the correct levels of oxidation by either analysis. Variance component estimates for flavor scores showed that the variation between sensory panelists within laboratories was lowest for the unaged oils. As storage time increased, the variance also increased, indicating that differences among panelists were greater for more highly oxidized oils. Between-laboratory variance of sensory panel scores was significantly lower than within-laboratory variance.     

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.     

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.     

An evaluation of commercial nickel catalysts during hydrogenation of soybean oil

The activities of several commercial nickel catalysts were determined by measuring their activation energies. Among these catalysts, G95E, Resan 22, Nysosel 222 and 325, all with low activation energy, were more active than DM3 and G95H, which had higher activation energy. However, the less active catalysts increased the linoleate selectivity of soybean oil during hydrogenation. The yields of bothtrans isomers and winterized oil were higher for the more selectively hydrogenated oil catalyzed by the less active catalysts. In the sensory evaluation, the fractionated solid fat that contained moretrans isomers was lower in flavor scores than the fractionated liquid oil after hydrogenation and winterization of soybean oil.     

Application of the Fluorescent Light Test and Some Other Methods for Determination of the Stability of Different Edible Oils

For the stability determination of different kinds of edible oils (sunflower, corn and soybean) various methods have been applied: Fluorescent light test, AOM-method, Oventest and Stability at room temperature. The fatty acid composition, the tocopherol content and the quality characteristics (peroxide value, anisidine value, content of dienes and trienes) were determined before testing of the stability. Special attention has been given to the determination of stability by the Fluorescent light test. This test seems to be very interesting in the determination of oil stability because the action of light is the main factor for the deterioration of the oil, while it is in the supermarkets in clear glass or plastic bottles (oil is not packed in brown glass in Yugoslavia). Oil in 1 liter original glass or plastic bottles or in 50 cm³ jars was exposed to the influence of the light of four 40 W fluorescent cool-white tubes of 1 m. Oxidation rate of the samples was followed by measuring the peroxide value. For the organoleptic evaluation, a three-member panel judged the flavor on a 10 point scale. The obtained results show that, under the conditions of this test, corn oil has the best stability. Sunflower oil has two and half time better stability than soybean oil. Some correlation has been established between the stability obtained by all applied methods.     

Edible oil evaluation by room odor tests: A preliminary report

Room odors developed on heating edible fats in open vessels were evaluated and characterized by a 20 member odor panel. Edible fats tested were: special soybean salad and cooking oils, hydrogenated soybean oil and some commercial salad and cooking oils. Factors were investigated that affect reliability and reproducibility of the test and the acuity of the panel members. The effects of fry temperature and size of sample were investigated. The method has been applied to a study of hydrogenated and unhydrogenated soybean oil samples. Presented at the AOCS Meeting, Chicago, September 1970. No. Market. Nutr. Res. Div., ARS, USDA.     

Flavor and oxidative stability of hydrogenated and unhydrogenated soybean oils: Effects of antioxidants

Flavor and oxidative stabilities were studied by organoleptic evaluation and chemical analysis of three different samples of soybean oil: unhydrogented (I); hydrogenated with nickel catalyst (II); and hydrogenated with copper-chromium catalyst (III). Analyses for these oils were: I II III iodine Value 138 109 113 Linolenate, % 8.3 3.3 0.4 Each oil was deodorized with the addition of either citric acid alone or citric acid plus BHA and BHT antioxidants. Addition of antioxidants did not improve the flavor stabilities of the oils in accelerated storage tests but did improve the flavor stabilities of II and III in light exposure tests. All three oils that received the same additive treatment had equivalent flavor stability in both accelerated storage and light exposure tests. However, both hydrogenation and antioxidant treatment improved oxidative stability as measured by the Active Oxygen Method. There was good correlation between flavor score and the logarithm of the peroxide value determined at the time of tasting. Presented at the AOCS Meeting, New York, May 1977.     

Flavor stability of soybean oil. 1. The role of the non-saponifiable fraction

Summary It has been found that the addition of the nonsaponifiable extract of hydrogenated soybean oil to either refined cottonseed oil or refined peanut oil caused these oils to develop odors and flavors characteristic of reverted soybean oil. The non-saponifiable material from linseed oil did not produce a similar effect. When the non-saponifiable extract of hydrogenated soybean oil was added to mineral oil, a sweet, syrupy odor and flavor developed. By selective absorbents it was possible to produce a much greater improvement in hydrogenated than in unhydrogenated soybean oil. These observations are discussed in terms of their relationship to the various theories on the mechanism of reversion.     

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. Presented in part at the AOCS meeting, New York, October 1968 ARS, USDA     

Electrochemical hydrogenation of edible oils in a solid polymer electrolyte reactor. Sensory and compositional characteristics of low Trans soybean oils

Soybean oils were hydrogenated either electrochemically with Pd at 50 or 60°C to iodine values (IV) of 104 and 90 or commercially with Ni to iodine values of 94 and 68. To determine the composition and sensory characteristics, oils were evaluated for triacylglycerol (TAG) structure, stereospecific analysis, fatty acids, solid fat index, and odor attributes in room odor tests. Trans fatty acid contents were 17 and 43.5% for the commercially hydrogenated oils and 9.8% for both electrochemically hydrogenated products. Compositional analysis of the oils showed higher levels of stearic and linoleic acids in the electrochemically hydrogenated oils and higher oleic acid levels in the chemically hydrogenated products. TAG analysis confirmed these findings. Monoenes were the predominant species in the commercial oils, whereas dienes and saturates were predominant components of the electrochemically processed samples. Free fatty acid values and peroxide values were low in electrochemically hydrogenated oils, indicating no problems from hydrolysis or oxidation during hydrogenation. The solid fat index profile of a 15∶85 blend of electrochemically hydrogenated soybean oil (IV=90) with a liquid soybean oil was equivalent to that of a commercial stick margarine. In room odor evaluations of oils heated at frying temperature (190°C), chemically hydrogenated soybean oils showed strong intensities of an undesirable characteristic hydrogenation aroma (waxy, sweet, flowery, fruity, and/or crayon-like odors). However, the electrochemically hydrogenated samples showed only weak intensities of this odor, indicating that the hydrogenation aroma/flavor would be much less detectable in foods fried in the electrochemically hydrogenated soybean oils than in chemically hydrogenated soybean oils. Electrochemical hydrogenation produced deodorized oils with lower levels of trans fatty acids, compositions suitable for margarines, and lower intensity levels of off-odors, including hydrogenation aroma, when heated to 190°C than did commercially hydrogenated oil.     

An emulsion method for the sensory evaluation of edible oils

The flavor intensity of soybean oils was evaluated in emulsions stabilized with gum acacia. A 10-point scale was used with a blank to establish the bland end of the scale and a standard diacetyl solution to establish a point near midscale. Tasting oils in emulsion gave significantly different scores than tasting oil directly. Evaluation in emulsion decreased panel error for poor quality oils but not for very bland oils. At least six samples could be tasted in emulsion without casusing panel fatigue or reducing accuracy. The concentration of oil in the emulsion could be adjusted to increase sensitivity to weak flavors or improve the evaluation of intensely flavored oils. Soybean oils containing various amounts of linolenic acid were evaluated by the emulsion method, and those with lesser amounts of linolenic acid were shown to be more stable. A gas Chromatographic total volatile method was shown to correlate fairly well with sensory evaluation of oils tasted in emulsions under conditions where both flavors scores and total volatiles changed significantly with time. Journal Paper no. J-10442 of the Iowa Agriculture and Home Economics Experiment Station, Ames. Project no. 2143.