J. M. Snyder

Effect of moisture and particle size on the extractability of oils from seeds with supercritical CO2

Moisture level and particle size of soybeans, peanuts and cottonseed were correlated with the extraction rate and yield of oil when extracted with supercritical carbon dioxide (SC-CO2) at a constant temperature (50 C) and pressure (8000 psig). The rate of extraction and ultimate oil yields were quite low with cracked soybeans. However, good extraction rates and nearly theoretical oil yields were obtained from ground or thinly flaked (<0.010″) seeds. Moisture levels between 3% and 12% had little effect on extracability. Oil composition was not influenced by either parameter. Scanning electron microscopy was used to study seed structure before and after extraction with SC-CO2. Micrographs of SC-CO2-extracted seeds were similar to hexane-extracted seeds.

Capillary gas chromatographic analyses of headspace volatiles from vegetable oils

Eight different vegetable oils obtained commercially were analyzed for volatiles by capillary gas chromatography (GC). Volatiles generated in a GC static headspace sampler at 180 C were injected automatically onto a chemically bonded capillary column. Only a small number of GC peaks of low intensity were observed in the fresh samples, which varied in peroxide values from 0.2 to 3. Several major peaks were evident in the oils aged eight and 16 days at 60 C with peroxide values ranging from 16 to 65. Thirty-four GC peaks were identified on the basis of relative retention time of reference compounds and on the basis of gas chromatography-mass spectrometry (GC-MS). Volatile compounds identified were those expected from the autoxidation of principal unsaturated fatty acid components of each vegetable oil tested. The relative concentrations of volatile components increased with the level of oxidation as determined by peroxide value.

Comparison of gas chromatographic methods for volatile lipid oxidation compounds in soybean oil

To develop new knowledge on undesirable flavors affecting the quality of foods containing polyunsaturated lipids, we investigated the volatiles in soybean oil oxidized at different conditions by three capillary gas chromatographic methods: (a) direct injection (5 min heating at 180 C); (b) static headspace (20 min heating at 180 C, pressurizing for one min), and (c) dynamic headspace (purging 15 min at 180 C onto a porous polymer trap, desorbing from trap for five min). A fused silica column was used with bonded polymethyl and phenyl siloxane phase. At peroxide values between 2 and 10, the major volatile products found in soybean oil by the three methods were pentane, hexanal, 2-heptenal, 2,4-heptadienal and 2,4-decadienal. The intensities of each volatile compound varied with the analytical methods used.

cis-trans isomerization of unsaturated fatty acids withp-toluenesulfinic acid

Elaidination of unsaturated fatty acids usingp-toluenesulfinic acid yielded 77–80% totaltrans unsaturation in the products. Results from reactions with monoene, diene, and triene isomers indicated that only geometric isomerization takes place. Each double bond isomerized randomly and independently in the polyunsaturated fatty acids. Reactions proceeded quickly, and the method proved convenient and reliable.

A methodology study to evaluate quality of soybeans stored at different moisture levels

The quality of soybeans and oil extracted from seeds stored at different moisture contents was evaluated by static headspace gas chromatography, near-infrared spectrometry, fluorescence measurements, and silicic acid chromatography. Headspace gas chromatographic analysis of both ground beans and crude oils provided a sensitive measure of oxidative deterioration based on hexanal and total volatiles. Near-infrared analyses at 2260 nm showed a correlation coefficient of 0.864 with titratable free fatty acids. Fluorescence measurements on chloroform-methanol extracts were much less sensitive and showed an increase only in the most damaged samples. Silicic acid chromatography of crude oils showed a significant decrease of polar lipids and increase of less polar lipids with storage at high moisture levels, in agreement with the decrease in phosphorus observed. Among the methods tested, headspace gas chromatography is most sensitive to evaluate oxidative deterioration, and near-infrared analysis is most suitable and rapid to evaluate hydrolytic deterioration in stored soybeans. This methodology can be used to evaluate factors affecting the food quality of soybeans for domestic and foreign markets.

Headspace volatile analysis to evaluate oxidative and thermal stability of soybean oil. Effect of hydrogenation and additives

Headspace gas chromatographic analysis of heated soybean oil was investigated as a tool to determine what effect hydrogenation and additives have on the formation of total and individual volatile components. Soybean oil was hydrogenated to varying linolenate (Ln) contents with either nickel (Ni) or copper catalysts. Oils were stabilized with citric acid (CA) or a combination of CA with tertiary butyl hydroquinone (TBHQ) and/or methyl silicone (MS). Volatiles were analyzed with a capillary gas chromatography equipped with a headspace sampler positioned on the injector. Oxidative stability was determined after storage of the oils at 60 C. To study thermal abuse and frying performance of oils, samples were heated for several, hours with prolonged bread frying. The deterioration of the oil was accelerated further by static heating in air within the headspace sampler. All hydrogenated oils produced less total volatiles than the unhydrogenated control oil after prolonged heating and bread frying. Static heating at 190 C for one hr showed that the oil hydrogenated with Ni to 0.4% Ln was the most stable. MS decreased the formation of volatiles in all samples and was particularly effective, in stabilizing the hydrogenated oils. However, MS had little effect on volatiles in the oil hydrogenated to 0.4% with Ni. Unique volatile compounds identified included 2,4-heptadiental in nonhydrogenated soybean oil and 2-nonenal in most hydrogenated oils. On heating, the amount of 2-heptanal decreased significantly in the Ni hydrogenated oils compared to the control. Hexanal, on the other hand, decreased in all hydrogenated oils compared to the control.

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.

Reuse of copper catalyst in continuous hydrogenation

Continuous hydrogenation of soybean oil using copper catalyst can be improved economically by reusing the catalyst. A hydrogenated oil with an approximate iodine value drop of 25 was attained by regulating the conditions and size of the reactor. Catalyst was removed by centrifuge and recycled. Reaction products were evaluated to determine catalyst activity, linolenate selectivity andtrans formation. By adding 0.2–0.4% fresh catalyst each time, the activity was retained. Linolenate selectivity ranged from 6 to 11 andtrans formation, expressed as specific isomerization, ranged from 0.63 to 0.78.

Laboratory-scale continuous hydrogenation

Data required for modeling and simulation of continuous hydrogenation kinetics have been obtained in an isothernal, cocurrent flow-type reactor. A preheated suspension of catalyst in oil, mixed with hydrogen, is passed cocurrently through 10 m length of 0.12 cm ID Teflon tubing at flow rates varying from 1.5 to 4.5 ml/min, gas flow rates from 100 to 700 ml/min, and temperatures from 150 to 190 C. The hydrogenations are run using nickel catalyst at outlet pressures of one atmosphere. Samples are removed at equal intervals along the length of the reactor and analyzed by gas chromatography. The kinetics of the continuous reactor are satisfactorily modeled by the simple scheme Ln→Lo→01→S using first order kinetics. Reaction rates, calculated by a digital computer, are shown to be related to temperature by the Arrhenius equation.trans Content and degree of hydrogenation are increased with temperature are decreased as oil flow increases. Hydrogen flow rate has little or no effect over the range studied.

Competitive hydrogenation rates of isomeric methyl octadecadienoates

Determination of the relative reaction rates of isomeric methyl octadecadienoates is possible by competitive reduction of a mixture containing an inactive diene and a radioactively labeled isomer. The hydrogenation rate of methylcis-9,cis-12-octadecadienoate with platinum and nickel catalysts is compared to the hydrogenation rate of each of several isomers of methyl octadecadienoate, and the relative rate of the competitive hydrogenations is calculated by a digital computer. Methylcis-9,cis-12 linoleate is reduced the most rapidly of all the dienes studied. The relative rates of the positional isomers tend to decrease with the increasing number of methylene groups between the double bonds, except when one of the double bonds is in the more reactive 15 position. Comparison of the geometric isomers shows thattrans,trans diene is hydrogenated at a slower rate thancis,cis linoleate.