Laboratory investigations on the extraction of oil from vegetable oil-cakes with ethanol

1. Undue dilution of alcohol can be prevented by employing oleaginous materials of moisture content less than 1.0% for ethanol extraction.
2. The residual oil content of the meal depends on the particle size of the cake for a constant period of extraction.
3. Better quality oil in respect to color and F.F.A. is obtained with 95.6% ethanol extraction though the temperature of extraction is higher than the temperature employed with 98.6% ethanol.
4. F.F.A. of the extracted oils is low and within 1.0% for most of the oils, hence a reduction of refining loss. The color of safflower and peanut oils compares with the color of the screw-press oils.
5. In the case of cottonseed meats extraction, the cooking of meats results in a lighter color oil and increases the yield for the same period of extraction. Cottonseed extraction also illustrates the advantages of ethanol as the solvent for oil extraction.

     

Effect of Various Pressure Cooking Conditions on Gossypol Content of Cottonseed Meal and Oil

Egyptian cottonseed meats were obtained from one of the largest Egyptian factories dealt with oil production in Egypt. Studies were carried out to demonstrate the favorable conditions for cooking meats to produce oil and meal low or even free of gossypol. Cottonseed meats were conditioned to four different levels of moisture and cooked at three different levels of pressure for two different cooking periods. The decrease (91.1%) of the free gossypol content in the meals depended mainly upon the moisture content of the conditioned meats and the cooking temperature rather than on the cooking period. While the decrease (96.5%) of the total gossypol content of oil was more pronounced by the increment of both the cooking period and the level of moisture content to which the meat was conditioned. Generally, moist pressure cooking decreased the protein content of meats by 8% and the free fatty acids of oil were decreased to 1.12–1.18%. Laboratory produced meats and oils were compared with those produced in the factory.     

Supercritical carbon dioxide extraction of cottonseed with co-solvents

Extraction of cottonseed lipids with supercritical carbon dioxide (SC-CO₂) was conducted with and without a cosolvent, ethanol or 2-propanol (IPA). At 7000 psi and 80°C, the reduced pressure, temperature and density of SC-CO₂ was at 6.5, 1.17 and 1.85, respectively; the specific gravity was 0.87. Under these conditions, CO₂ is denser than most liquid extraction agents such as hexane, ethanol and IPA. The extraction of cottonseed with SC-CO₂ gave a yield of more than 30% (moisture-free basis). This is comparable to yields obtained by the more commonly used solvent, hexane. The crude cottonseed oil extracted by SC-CO₂ was visually lighter than refined cottonseed oil. This was substantiated by colorimetric measurements. No gossypol was detected in the crude oil. However, crude oil extracted by SC-CO₂, to which less than 5% of ethanol or IPA as co-solvent was added, containedca. 200 ppm of gossypol, resulting in the typical dark color of cottonseed crude oil with gossypol. CO₂ extracted a small amount of cottonseed phosphatides, about one-third of that extracted by pure ethanol, IPA or hexane. A second extraction with 100% ethanol or IPA after the initial SC-CO₂ extraction produced a water-soluble lipid fraction that contained a significant amount of gossypol, ranging between 1500 and 5000 ppm. Because pure gossypol is practically insoluble in water, this fraction is believed to be made up of gossypol complexed with polysaccharides and phosphatides. Partially presented at the AOCS 1993 Annual Meeting & Expo in Anaheim, California.     

Pilot plant development of the alkali cooking process for cottonseed meats. I. Effect of flake,thickness and of time,temperature, and moisture content during cooking

Summary and Conclusions Results obtained from alkaline cooking experiments show that all of the four variables studied—cooking mousture content, temperature, time and flake thickness—influenced the properties of the resultant meals in varying degrees. Under the experimental conditions used a high initial moisture content, above 18%, is necessary to lower the free gossypol content in the finished meal to less than 0.04%. When this amount of moisture is used, a plastic mass results at the beginning of the process which requires special equipment to supply the mechanical action necessary to break the pigment glands at a low temperature. In the presence of high moisture content and alkali the gossypol, which is released when the glands are ruptured, is bound to the meal. When sufficient initial moisture is present (24–31%), only traces of gossypol (0.010% or less) are found in the extracted crude oil. High temperatures in the presence of high moisture content reduce the solubility of the meal protein (in 0.02N NaOH). Under the conditions of moisture, temperature, and time of cooking used in the experiments the maximum nitrogen solubility obtained under conditions necessary to produce low free gossypol content was 64%. This differs from results obtained in previous work performed under different conditions. A probable reason for the difference is given based on the interrelationship of the three variables. The results demonstrated further that finer comminution of the raw meats by rolling to 0.005-in. thick flakes results in lower free gossypol content in the finished meal and lower gossypol content of the oils as well as more complete removal of the oil by the filtration-extraction procedure used. One of the laboratories of the Southern Utilization Research Branch. Agricultural Research Service, U. S. Department of Agriculture.     

Effect of Sodium Hydroxide and Other Salts on Gossypol Content of Cottonseed Meal and Oil

Egyptian cottonseed meats used for oil production were obtained from one of the factories dealt with oil production in Egypt. The meats were cooked with some salts by using paraffin oil bath prior to oil extraction. The study revealed that different volumes of sodium hydroxide solutions of various concentrations when added to cottonseed meats before cooking greatly reduced the free gossypol content and the total gossypol of meals and oils by 28.3 to 92.9 and 17.9 to 100%, respectively. The extent of reduction depend mainly on the volume of the alkaline solution rather than on its concentration. The oil had a low free fatty acids content (0.33%) due to the alkali treatment. Cooking cottonseed meats with 1.85% calcium hydroxide and 0.5% ferrous sulphate solutions, reduced the gossypol content of the crude oil by 91%. The oil had colour of 9 red units, and free fatty acids content of 0.59%. This treatment completely diminshed the free gossypol content of meal. The crude protein content of the meals was decreased by 6 to 7%. This may be attributed to the loss of nitrogen due to the cooking by using the paraffin oil bath.     

Cottonseed preparation

Conventional methods of cottonseed preparation are reviewed and described, including seed cleaning, saw delinting, dehulling, conditioning, and flaking. The use of screw presses for prepress conditioning ahead of solvent extraction is discussed as compared to conditioning for direct solvent extraction. Newer methods and proposed alternate methods of cottonseed preparation are discussed including: abrasive delinting, acid delinting by gas and liquid acid, and the decorticating of undelinted seed. The effect of cracking rolls, moisture addition, moist cooking and flaking on gossypol gland rupture, the binding of gossypol to protein, and the effect of these processing or preparation variables on the residual oil in the extracted meal and on the oil quality are discussed.     

Effect of Cooking Cottonseed Meats in the Presence of Borax on the Quality of Meals and Oils

Studies were carried out on cottonseed meats obtained from one of the largest Egyptian factories dealt with oil production. The studies aimed to demonstrate the effect of two different methods of cooking cottonseed meats treated with various concentrations of borax on the gossypol content and on some properties of meals and oils. The results indicated that the borax concentration required to decrease the free gossypol content of the meal by 93% and to completely diminish the total gossypol content of the oil depended on the methods of cooking the meats. The crude oil obtained from the borax treated cooked meats was of very light colour and was easily bleached. The crude protein content of the meals was not affected by the borax concentration but was decreased upon cooking by using the paraffin oil bath.     

Processing of cottonseed

1. The pigmentation of cooked cottonseed has been shown to depend principally upon the moisture content and period of heating of the seed.
2. Several samples of crude hydraulic-pressed and screw-pressed oils produced under known processing conditions were found to differ markedly from each other with respect to their original colors and refining characteristics.
3. The screw-pressed crude oils were more deeply colored and contained one principal pigment, whereas the hydraulic-pressed oils contained two principal pigments.
4. The absence of significant amounts of gossypol in the crude oils has been demonstrated by means of a new technic for the quantitative isolation of gossypol.
5. The crude oil pigments differed from gossypol, but like gossypol, they were removed during alkali refining.
6. The pigmentation of the crude oils has been shown to depend principally upon the pigmentation of the original seed and the moisture content of the seed during cooking.
7. On the basis of their absorption spectra it has been deduced that the alkali-refined hydraulic-pressed oils contain two to three pigments originally present in the crude oils whereas the alkali-refined serewpressed oils contain these same pigments as well as a large number of decomposition products of the principal crude oil pigment.

     

Cottonseed extraction with mixtures of acetone and hexane

Cottonseed flakes were extracted with mixtures of n-hexane and acetone, with the concentration of acetone varying between 10 and 75%. Adding small amounts of acetone (≤25%) to n-hexane significantly increased the extraction of free and total gossypol from cottonseed flakes. Sensory testing detected no difference in the odor of cottonseed meals produced either by extraction with 100% n-hexane or by extraction with a 10∶90 (vol/vol) mixture of acetone/hexane. More than 80% of the free gossypol was removed by the 10∶90 mixture of acetone/hexane, whereas pure n-hexane extracted about 47% of the free gossypol from cottonseed flakes. A solvent mixture containing 25% acetone removed nearly 90% of the free gossypol that was removable by extraction with pure acetone; the residual meal had only a minimal increase in odor. In contrast, cottonseed meals produced by extraction with pure acetone had a much higher odor intensity. The composition of the cottonseed crude oil was insignificantly affected by the acetone concentration of the extraction solvent. The results indicate that mixtures of acetone and n-hexane can be used as extraction solvents to produce cottonseed crude oil without the concomitant development of odorous meals.     

The reduction of free gossypol in cottonseed flakes during solvent extraction

Conclusions Extraction with trichloroethylene was found to be an effective method of reducing the free gossypol content of flaked cottonseed meats. The reduction was found to be a function of both extraction temperature and residual extractables in the extracted meal. Because of the low temperatures involved the meal produced by this method has a higher soluble protein content than a meal in which the free gossypol is reduced by heat treatment.     

Solvent extraction of cottonseed meats

In the experimental countercurrent extraction of flaked cottonseed meats by trichloroethylene the residual oil content of the extracted flakes decreased with: first, a decrease in the final oil content of the final miscella; second, decrease in the flake moisture down to 8.64%; third, decrease in flake thickness; fourth, increase in temperature; and fifth, increase in extraction time. For the batch of cottonseed meats used the following equation was developed: whereR is percent residual extractables,b is flake thickness in feet,D is meat diameter in feet,ϑ is extraction time in hours,μ in viscosity, lb. per ft. hr.,ρ is density, lb. per cu. ft., andt is extraction temperature in degrees F. Not enough data were secured by extraction with hexane to check the equation developed for trichloroethylene extraction. Hexane is a poorer solvent for cottonseed oil than trichloroethylene. The amount of oil remaining in the meal is affected to a greater extent by the miscella concentration in hexane extraction than in trichloroethylene extraction.     

Cottonseed extraction with a new solvent system: Isohexane and alcohol mixtures

A solvent system, consisting of isohexane and 5 to 25% alcohol, either ethanol (EtOH) or isopropyl alcohol (IPA), was tested for extracting gossypol and oil from cottonseed. The test results indicate that this new solvent system not only is effective in removing free and total gossypol but also is as efficient as n-hexane when extracting oil. The amino acid analysis of cottonseed meal, produced by the new solvent system, is similar to that produced by commercial n-hexane. Present commercial cottonseed extraction and downstream processing of cottonseed oil refining may need little change to adopt this new solvent system. This new solvent system may lead to a solution to the gossypol problem of cottonseed extraction.     

Isopropanol as a solvent for extraction of cottonseed oil

Phase equilibrium data for the system; cottonseed oil-isopropanol-water were determined at 30°C. and compared with data for the system; cottonseed oilethanol-water. The relative phase distribution of fatty acids and cottonseed oil in mixtures with isopropanol and water was studied under varying conditions of water and fatty acid concentrations. These tests showed the fatty acids to be highly concentrated in the alcohol-water phase. Flaked cottonseed meats were extracted in continuous extraction apparatus with 91% isopropanol, 99% isopropanol, and mixtures of commercial hexane and isopropanol. Analytical data on the extractions show that 91% isopropanol is an efficient solvent for extracting active gossypol along with the oil. Rat and swine feeding tests of the isopropanol extracted meal showed it to be highly superior to hydraulic meal as a source of protein. A method was developed for treatment of the cottonseed-isopropanol miscella by liquid-liquid extraction to separate purified oil and fatty acid fractions from other materials in the extract.     

Gossypol material balance,denaturation of protein,and loss of thiamine in commercial processing of cottonseed

Summary The processing of cottonseed by five commercial mills has been systematically examined with reference to free gossypol reduction, nitrogen solubility, thiamine reduction, material balances of total gossypol, and the distribution of gossypol in processing. One hydraulic mill reduced the free gossypol in the meal to a low level, approximating the level obtained in screw pressing. For a given mill the free gossypol contents of the meals were found to be fairly uniform. Low free gossypol content of hydraulic-pressed meals depends on the thoroughness with which the gossypol is bound in the cooking. Gossypol is bound in both the cooking and pressing in the production of screw-pressed meals. A relatively small amount of total gossypol is lost or destroyed in processing cottonseed by either hydraulic- or screw-pressing methods. This small loss occurs while the meats are being prepared for pressing. No significant loss was found which could be attributed to the pressing operations. Serew-pressed oils appear to contain several times as much gossypol as hydraulic-pressed oils, with the amount dependent on the extent of the binding of gossypol in the cooking and mechanical preparation of the meats for pressing. The high temperatures developed in screw pressing contributed to a higher reduction in thiamine and nitrogen solubility than was observed for hydraulic pressing. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.     

Concerns for the determination of free fatty acid in cottonseed

The official AOCS method for the determination of free fatty acid (FFA) in cottonseed requires dehulling the seed, grinding the meats with a 12-blade food processor, and extracting the ground meats in a butt tube with three portions of room-temperature petroleum ether. The extracted oil, after desolventization, is then titrated with NaOH to the end point of phenolphthalein in a mixed solvent of isopropanol and hexane. Our study showed that this procedure tends to underestimate the amount of FFA present in the oil of cottonseed by as much as 11.5%. It was also found that to obtain consistent and accurate FFA content, a desirable particle size is smaller than 10 mesh (preferably <14 mesh), minimum extraction temperature should be no less than 40°C (preferably greater than 50°C), and the extraction time should be longer than 2 h in a Soxhlet extractor.     

Solubility of cottonseed proteins in hydrochloric acid

Summary The correlations between the growth response of chicks to the nine cottonseed meals fed as a protein supplement and the solvent powers of 0.02N NaOH, 6N HCl, and 0.5N NaCl for cottonseed meal proteins are almost identical. The correlations between the solvent power of 6N HCl, 0.02N NaOH, and 0.5N NaCl and the gossypol contents of the meals are not as good as the correlations between the solvent powers of these solutions and the growth response of chicks. One of the laboratories of the Southern Utilization Research and Development Division. Agricultural Research Service, U. S. Department of Agriculture.     

Pilot plant studies on extracting cottonseed with methylene chloride

The practical feasibility of using methylene chloride to extract oil, aflatoxin and gossypol simultaneously from cottonseed flakes was demonstrated in a 56-hr experimental run using a pilot-scale, continuous extractor. Nine different trials varying in extraction time, solvent:flake ratio, flake preparation method and blending with 5% ethanol were evaluated. Residual oil contents were lower than typically achieved in extraction with hexane. Aflatoxin contents of the meals were reduced by 73–92% of the level in cottonseed meats, making possible the upgrading of a large portion of cottonseed meal that otherwise would exceed current action levels. Because gossypol also was extracted, it was possible to produce cottonseed meal that was well suited for use in poultry feeds, especially when a blend of 5% ethanol in methylene chloride was used. Meal desolventized easily, and residual levels of methylene chloride were generally less than 12 ppm. The oil was refined and bleached to acceptable quality standards, and no residual aflatoxin was detected in alkali-refined oil.     

Properties of oil extracted from cottonseed with acetone-hexane-water solvent mixture

Slightly more neutral oil was obtained on the exhaustive extraction of raw cottonseed meats with the acetone-hexanewater (AHW) solvent mixture than was obtained under the same conditions with commerical hexane. Although most of the gossypol originally present in the seed is extracted with the oil when the AHW solvent mixture is used, the crude oils refined and bleached to yield oils of excellent colors. Methods of recovery of the solvent from the mixed solvent miscellas are reported, together with the refining and bleaching data for the recovered oils.     

Note on gossypol and its relation to color fixation in cottonseed oil

1. The crude oils studied contained from 0.00 to 0.04% gossypol.
2. Much of the gossypol added to crude cottonseed oils disappeared in one hour.
3. The disappearance of gossypol from refined, bleached, and deodorized cottonseed oil, from highly purified tripelargonin, and from ethyl acetate is demonstrable after the lapse of one hour.
4. It is suggested that the initial reaction of gossypol in the oils is an ester exchange reaction.
5. It is further suggested that secondary reactions result in the production of a red coloration product that is not removable from the oil by the standard refining and bleaching methods.

     

Comparative absolute yields of crude and neutral oils from variously prepared cottonseed meats

Summary Experiments utilizing cottonseed meats of diverse origin and composition were conducted for the purpose of determining the effect of the method of meats preparation on the yields of crude and neutral oil obtainable from differently prepared, comparable meats by solvent extraction. Three methods of meats preparation were employed,i. e., simple flaking of raw meats “as is”, tempering of cracked meats prior to flaking, and cooking by the modified hydraulic method developed for use with the filtration-extraction process. Commercial hexane was used as the extraction solvent. The experiments were carried out by procedures which eliminated the effects of any variables other than the method of preparing the meats for extraction The results of the studies showed that the method used in preparing cottonseed meats for extraction had a significant effect on the yields of crude oil obtained but that the yields of neutral oil, the valuable constituent of crude oils, were virtually unaffected. Analyses of the crude oils showed that the differences in crude oil yields were caused by the relative amounts of non-neutral oil materials in the crudes from the differently prepared meats. The greatest yields of crude oil were obtained from raw flakes, intermediate yields from tempered flakes, and the smallest yields from cooked flakes. The impurities content in the respective crude oils followed the same order,i. e., crudes from raw flakes were highest in impurities and lowest in neutral oil, crudes from tempered flakes were lower in impurities and higher in neutral oil, and the crudes from the cooked meats were outstandingly low in impurities and high in neutral oil. Virtually equal amounts of neutral oil were obtained from equivalent quantities of comparable meats regardless of the method used in preparing the meats for extraction. Presented at the meeting of the American Oil Chemists’ Society, Chicago, Ill., September 24–26, 1956. One of the laboratories of the Southern Utilization Research Branch, Agricultural Research Service, U.S. Department of Agriculture.