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     

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.     

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.     

Analyses of flavor qualities of vegetable oils by gas chromatography

Soybean oil, hydrogenated soybean oil, and corn oil were exposed to fluorescent light for different periods of time to obtain a wide range of flavor qualities. The flavor qualities of these oils were evaluated by sensory and gas Chromatographic methods. Sensory evaluation was conducted using a 10-point hedonic scale to rate overall flavor quality. The sensory panel was made up of 94 members from 8 different laboratories. The correlation coefficients (r) of the flavor scores between sensory evaluation and instrumental analysis for soybean oil, hydrogenated soybean oil, and corn oil were 0.95, 0.97 and 0.97, respectively. These results were very close to the correlation coefficients (r) 0.99, 0.98 and 0.95 obtained from 10 sensory panel members from one specific laboratory.     

Conversion of polyunsaturates in vegetable oils tocis-monounsaturates by homogeneous hydrogenation catalyzed with chromium carbonyls

Chromium carbonyl complex catalysts were used to selectively hydrogenate polyunsaturates in vegetable oils into products retaining 90% to 95%cis configuration and their liquid properties. The product from soybean oil contained 42–69% monoene, 10–40% diene and 0–4% triene. The product from safflower oil contained 73–82% monoene and 8–17% diene. About 45–55% of the double bonds in monoenes from hydrogenated soybean oil remained in the C₉ position, and the rest was distributed between C₁₀, C₁₁, and C₁₂. Preliminary oxidative and flavor stability evaluations showed that these hydrogenated soybean oils compared favorably with a commercial sample of hydrogenated-winterized soybean oil. Liquid fatty acids prepared by saponification of hydrogenated soybean and safflower oils (IV 90–100) had analyses about the same as those of commercial oleic acid. Presented before the Division of Agricultural and Food Chemistry, 156th American Chemical Society National Meeting, Atlantic City, N.J., September 1968.     

An evaluation of the oxidative and flavor stability of stored soybean oils

Results of 4-year storage tests are reported for crude and refined soybean oils held in 50-gal drums under conditions simulating field tank operations. Once-refined oils stored in filled drums without breathers showed lower peroxide values and lower dimer contents than oil stored in full drums with breathers. Refined oils in half-filled drums exhibited higher storage temperatures and, consequently, higher peroxide values and dimer contents than any other storage condition. Nondegummed and degummed crude oils held in drum storage had lower peroxide values and lower dimer contents than refined oils stored under similar conditions. Relationships are significant not only between storage peroxide values and dimer contents, but also each of these with flavor scores. Evidently, stored crude or stored refined soybean oils with peroxide values under 60 could be deodorized to produce salad-grade oils with initial flavor quality equal to that of oils processed from stocks having considerably lower initial peroxide values. The relative rate of peroxide increase for field tank storage can be estimated from linear regression analysis on data from stor-age of soybean oil in drums. Once-refined soybean oil held under large field tank storage conditions would not be expected to reach peroxide levels of 60 until after 3-4 years, even in warm areas. ARS, USDA. No. Utiliz. Res. Dev. Div.. ARS, USDA.     

Analysis of vegetable oil volatiles by multiple headspace extraction

Quantitative determination of the volatiles produced from oxidized vegetable oils is an important indicator of oil quality. Five vegetable oils, low-erucic acid rapeseed, corn, soybean, sunflower and high oleic sunflower, were stored at 60°C for four and eight days to yield oils with several levels of oxidation. Peroxide values of the fresh oils ranged from 0.6 to 1.8 while those of the oxidized oils were from 1.6 to 42. Volatile analysis by the multiple headspace extraction (MHE) technique, which includes a pressure and time controlled injection onto the gas chromatography (GC) column (a chemically bonded capillary column), was compared with that obtained by static headspace gas chromatography (SHS-GC). Several volatile compounds indicative of the oxidation of polyunsaturated fatty acids from the vegetable oils were identified and measured by MHE; pure compounds of twelve major volatiles also were measured by MHE, and peak area was determined. Multiple extractions of the oil headspace provided a more reproducible measure of volatile compounds than was obtained by SHS-GC. Concentration of all volatiles increased with increased oxidation as measured by peroxide value of the oil. Presented at the Annual American Oil Chemists' Society Meeting, May 8–12, 1988, Phoenix, AZ.     

Flavor and oxidative stability of hydrogenated and unhydrogenated soybean oils. Efficacy of plastic packaging

Soybean oils were packaged in polyvinylchloride, acrylonitrile, clear glass and amber glass bottles and their flavor stabilities were evaluated by a trained sensory panel. Hydrogenated and unhyrdogenated oils showed similar patterns of flavor deterioration regardless of container or type of aging. In accelerated light-exposure tests with air in the headspace, oils in plastic bottles showed flavor and oxidative stability equivalent to the same oils in clear glass bottles. Packaging in the amber glass bottle provided, as expected, significantly improved oil stability during light-exposure tests. In accelerated storage tests at 60 C with air in the headspace, sensory evaluation and peroxide determination showed no significant differences in oils packaged in clear glass and PVC, but sometimes oils received lower scores in glass compared with those in acrylonitrile bottles. During long-term storage, oils in plastic bottles with nitrogen in the headspace had flavor and oxidative stabilities equal to oils in glass bottles with nitrogen. These investigations indicate that packaging soybean oils in polyvinylchloride or acrylonitrile bottles is a viable alternative to packaging in clear glass bottles.     

Correlation of the flavor scores of vegetable oils with volatile profile data

One of the most important quality parameters to users of commercial vegetable oils is the flavor. For years, taste panels have been used to rate the overall quality of oils in terms of flavor scores. However, flavor scores are subjective, vary considerably among individuals and laboratories, and are not really diagnostic. The need for more adequate quality evaluation of oils has focused attention on chemical changes and sensitive instrumental methods which can be used to differentiate the stage of freshness or deterioration. Dupuy’s direct gas Chromatographic method for the examination of the volatile profile of vegetable oils has been applied to 23 fresh soybean oils, and the same 23 oils aged 5 wk in the light at 22 C. High correlation between the volatile profile data and the flavor scores was found. The most significant peaks which were positively correlated with flavor score and those which were negatively correlated were obtained, and a prediction equation of flavor score was calculated from the volatile profile data. Presented at the AOCS Meeting, New Orleans, April 1976.     

Chemical inactivation of cyclopropenoid fatty acids in cottonseed meals and their physiological evaluation

Chemical inactivation of cyclopropenoid fatty acids in commercial cottonseed meals was explored with three classes of compounds: anhydrous gases, organic acids and sulfhydryl compounds. Of the reagents screened, sulfur dioxide reduced the cyclopropenoid content by over 90% while free cottonseed fatty acids and thioglycollic acid reduced the cyclopropenoid fatty acid content by over 30%. Large batches of the above three selected meals, as well as a control commercial screw-pressed meal, were then incorporated at 20 wt % levels in the rations of laying hens. A negative control containing 25% soybean meal and a positive control containing a 2% refined cottonseed oil of known CPA content were also employed. During a four-week feeding period, eggs were collected during the third and fourth week and stored at 35 F for periods of 3 and 6 months. Overall egg quality and the fatty acid distribution of the yolk lipids were determined after the 3 and 6 months’ storage periods.     

Minor components responsible for flavor reversion of soybean oil

Edible refined, bleached and deodorized (RBD) soybean oil was fractionated by silicic acid column chromatography to identify minor components responsible for flavor reversion. Minor components from oil eluted with diethyl ether/n-hexane (1:1) were compared with those from corn and canola oils. All vegetable oils contain free fatty acids, diglycerides and sterols as major ingredients in this fraction. However, unusual triglycerides consisting of 10-oxo-8-octadecenoic acid and 10-and 9-hydroxy octadecanoic acids were detected in RBD and crude soybean oils.     

Quantification of carbonyl compounds in oxidized low-linolenate,high-stearate and common soybean oils

The carbonyl compounds in five oxidized soybean oils (SBO) of various fatty acid compositions were determined. Three were from common normal soybean varieties, and two were from lines developed from new mutant varieties. One mutant line had a linolenate (18:3) content of 3.5% (A5), and one had a stearate (18:0) content of 24% (A6). SBO were stored at 28 C and 60 C. Trichlorophenylhydrazones (TCPH) of carbonyls formed during oxidation were quantified and tentatively identified by gas chromatography. The storage temperature and the composition of the oils affected the types and amounts of volatiles produced. Hexanal was the major volatile in the oils in both storage tests. After 60 C storage, 2- and/or 3-hexenal was present only in the oil with the highest 18:3 content (BSR 101, 18:3=9%). The amounts of the carbonyls formed in A5 were 2 to 5 times less than the amounts formed in BSR 101. The amounts of many of the carbonyls were converted into relative flavor potency by using reported data. Hexanal was the major contributor to flavor. After storage at 28 C, 2- and/or 3-hexenal was the second most intense flavor compound regardless of the 18:3 content of the oil. The amount of a compound and the threshold value did not always predict its flavor importance according to the flavor potency data.     

Replacement of peanut oil used for the fortification of sugar with vitamin A for other vegetable oils available in Central America

The objective of this study was to determine the technical feasibility of replacing the peanut oil used in the preparation of the premix to fortify sugar with vitamin A, for other vegetable oils available in Central America. For this purpose, cottonseed, soybean, corn and African Palm oils were tested. Premixes were prepared using each one of the oils and stored for evaluation during a six-month period. A premix prepared with peanut oil was used as a control. It was found that the stability of vitamin A was similar in all premixes; less than 10% of the original activity was lost through the duration of the study. The physical characteristics of the premixes were also acceptable, with the exception of the one containing soybean oil which became caked and rancid. The peroxide content of the oils contained in the premixes increased throughout the study period. The lowest level of oxidation occurred in the premix made with African Palm oil. Its peroxide content changed only from 1.4 to 8.8 mEq/kg of oil. In contrast, that containing soybean oil showed the greatest change in peroxide from 2.8 to 130.0 mEq/kg of oil. It was concluded that it is indeed technically feasible to substitute the peanut oil by another vegetable oil, which should be low in peroxides and of high stability. Furthermore, it should not alter significantly the stability of the vitamin A contained in the premix during storage. On this basis, the African Palm oil was the most suitable one.     

Supercritical CO2 degumming and physical refining of soybean oil

A hexane-extracted crude soybean oil was degummed in a reactor by counter-currently contacting the oil with supercritical CO₂ at 55 MPa at 70°C. The phosphorus content of the crude oil was reduced from 620 ppm to less than 5 ppm. Degummed feedstocks were fed (without further processing,i.e., bleaching) directly to a batch physical refining step consisting of simultaneous deacidification/deodorization (1 h @ 260°C and 1–3 mm Hg) with and without 100 ppm citric acid. Flavor and oxidative stability of the oils was evaluated on freshly deodorized oils both after accelerated storage at 60°C and after exposure to fluorescent light at 7500 lux. Supercritical CO₂-processed oils were compared with a commercially refined/bleached soybean oil that was deodorized under the same conditions. Flavor evaluations made on noncitrated oils showed that uncomplexed iron lowered initial flavor scores of both the unaged commercial control and the CO₂-processed oils. Oils treated with .01% (100 ppm) citric acid had an initial flavor score about 1 unit higher and were more stable in accelerated storage tests than their uncitrated counterparts. Supercritical CO₂-processed oil had equivalent flavor scores, both initially and after 60°C aging and light exposure as compared to the control soybean oil. Results showed that bleaching with absorbent clays may be eliminated by the supercritical CO₂ counter-current processing step because considerable heat bleaching was observed during deacidification/deodorization. Colors of salad oils produced under above conditions typically ran 3Y 0.7R.     

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.     

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. AOCS Bond Award Honorable Mention, Fall 1963. Biometrician, ARS Biometrical Service, stationed at Northern Laboratory. A laboratory of the No. Utiliz. Res. & 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.     

Volatile compounds in oils after deep frying or stir frying and subsequent storage

Soybean oil (900 g) was heated by deep frying at 200°C for 1 h with the addition of 0, 50, 100, 150 and 200 mL water, and then stored at 55°C for 26 weeks. Soybean oil, corn oil and lard were heated by stir frying and then stored at 55°C for 30 weeks. The volatiles and peroxide values of these samples were monitored. All samples contained aldehydes as major volatiles. During heating and storage, total volatiles increased 260-1100-fold. However, aldehyde content decreased from 62–87% to 47–67%, while volatile acid content increased from 1–6% to 12–33%; especially hexanoic acid which increased to 26–350 ppm in the oils after the storage period was completed. Water addition to the oils heated by deep frying tended to retard the formation of volatile compounds. The total amount of volatile constituents of lard heated by stir frying increased more during storage than that of corn oil or soybean oil. Peroxide values did not reflect the changes of volatile content in the samples.     

Margarine and shortening oils by interesterification of liquid and trisaturated triglycerides

Liquid vegetable oils (VO), including cottonseed, peanut, soybean, corn, and canola, were randomly interesterified with completely hydrogenated soybean or cottonseed hardstocks (vegetable oil trisaturate; VOTS) in ratios of four parts VO and one part VOTS. Analysis of the reaction products by high-performance liquid chromatography showed that at 70°C and vigorous agitation, with 0.5% sodium methoxide catalyst, the reactions were complete after 15 min. Solid-fat index (SFI) measurements made at 50, 70, 80, 92, and 104°F, along with drop melting points, indicated that the interesterified fats possess plasticity curves in the range of commercial soft tub margarine oils prepared by blending hydrogenated stocks. Shortening basestocks were prepared by randomly interesterifying palm or soybean oil with VOTS in ratios of 1:1 or 3:1 or 4:1, respectively. Blending of the interesterified basestocks with additional liquid VO yielded products having SFI curves very similar to commercial all purpose-type shortening oils made by blending hydrogenated stocks. Other studies show that fluid-type shortening oils can be prepared through blending of interesterified basestocks with liquid VO. X-ray diffraction studies showed that the desirable β′ crystal structure is achieved through interesterification and blending. Presented at AOCS Annual Meeting & Expo, Atlanta, Georgia, May 8–12, 1994.