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.     

The processing and storage characteristics of glandless cottonseed

Two consecutive storage tests of seven and six-months' duration were conducted to determine the relative effects of adverse storage conditions on glandless and glanded cottonseed and the products derived from each. The moisture conditions during storage resulted in extreme quality deterioration in both glandless and glanded seed. The damage sustained by glandless seed was not substantially different from damage occurring to glanded seed. Neither did glandless seed appear to deteriorate at a faster rate. Normal direct solvent extraction processing methods were followed to process seed for products quality evaluations as measured by nitrogen solubility, epsilon amino free lysine, and gossypol content for meals and FFA, cup refining loss, refined color, bleach color and gossypol content for oils. Oil from glandless seed refined and bleached to lower AOCS colors than corresponding glanded seed oils. Refining losses for oils from damaged seed were slightly higher for glandless seed oils. The meal quality from glandless seed was superior in all categories measured. A laboratory of the Cotton Research Committee of Texas operated by the Texas Engineering Experiment Station.     

The effect of processing conditions on the properties of screw-press cottonseed meal and oil

Summary Processing conditions, particularly cooking procedures, have a marked influence on the chemical properties of screw-pressed meal and oil. Cooking prepared meats at 240–250°F., as in normal mill practice, produced meals with low free gossypol content but at the expense of considerable protein damage. The resultant crude oils showed some color reversion upon storage at 95°F. Dry cooking (7% moisture) at temperatures not exceeding 200°F. gave meals of improved chemical properties, but the crude oils exhibited considerable color reversion on storage. Wet low-temperature cooking (200–210°F.), followed by evaporative cooling, yielded a meal intermediate in quality between that for normal mill practice and dry low-temperature cooking. The crude oils, which corresponded to hydraulic-pressed oil, did not exhibit any appreciable color reversion upon storage at elevated temperatures. The selection of processing conditions, notably cooking, enables wide variations in the distribution of gossypol between meal and oil. The increase in the bleach color of crude oils stored at 95–100°F. was found to be directly related to the initial gossypol content of the crude oils. Presented at 44th Annual Meeting of the American Oil Chemists’ Society, New Orleans, La., May 4–6, 1953. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Service, U. S. Department of Agriculture.     

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.     

A new method of detoxification of cottonseed by means of mixed solvent extraction

For several decades, scientists in the field of vegetable oils tried unsuccessfully to detoxify cottonseed by a practical method. By using 20-30% (by wt) of ethyl alcohol (90% in vol) with commercial hexane as a mixed solvent, we were able to extract effectively both gossypol and oil from cottonseed prepressed cake or flakes. Free gossypol in meal was reduced to ca. 0.013-0.04%; total gossypol was reduced to 0.32-0.55%; residual oil was reduced to ca. 0.5% or less. Any aflatoxin present also can be eliminated by this process. The detoxified cottonseed meal can be used as animal feed. Cottonseed protein can be used to substitute for soy protein. The extracted oil is of better quality than that obtained by the usual hexane extraction method, and gossypol is a valuable byproduct.     

Application of the antimony trichloride-spectrophotometric method to the determination of gossypol in cottonseed and cottonseed products

Summary A method is described which permits application of the antimony trichloride spectrophotometric method to the determination of gossypol in a variety of cottonseed products. Gossypol is determined by means of the following series of operations: 1. extraction of gossypol from cottonseed or cottonseed products by use of chloroform or aqueous ethanol; 2. isolation of gossypol from the extracts by use of aqueous alkali; and 3. application of the antimony trichloride-spectrophotometric test. Data are presented to show the results obtained by application of this procedure to the determination of gossypol in pigment glands, raw cottonseed meats, cooked cottonseed meats, hydraulic- and screw-pressed meals, solvent-extracted meals, gland-free meals, and oils, both expressed and solvent-extracted. Presented at the 39th Annual meeting of the American Oil Chemists' Society in New Orleans, May 4–6, 1948. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, 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.     

Solvent cooking of cottonseed meats for extraction

Data have been presented for a solvent-cooking method of preparing cottonseed meats for extraction. The study includes experiments in which the flake moisture contents were increased to as high as 40% during the initial solvent cooking phase and decreased to about 10% by the end of the cooking cycle, and in which hexane and heptane were used as the cooking solvent in the presence of chemicals such as NaOH, NaCl, CaCl₂, and NH₃. Results showed specific trends with varying condiditions. Examples are: increase in the initial moisture content during cooking increases granulation and consequently the mass velocity; increase to 30% moisture content is sufficient to result in mass velocities above the desirable 2,000 lbs. per square foot per hour; free gossypol content of the extracted meals is lower with the higher initial cooking moisture contents and with the addition of certain chemicals (NaOH-CaCl₂) ; and the addition of the combination of NaOH and NaCl resulted in better overall filtration-extraction characteristics than either the NaOH-CaCl₂ or the NH₃-NaCl combinations. On the basis of the above results the following general conclusions can be made:

1. Solvent cooking offers the possibility of combining cooking, crisping, and slurrying (extraction) steps into a single operation in a process, such as filtration extraction for the direct solvent extraction of cottonseed.
2. Chemicals can be introduced as needed to promote free gossypol reduction and possibly maintain a high alkali protein solubility in the solvent extracted meal.
3. Agglomeration and extractability of the solvent-cooked cottonseed meats can be controlled.

     

Processing methods to preserve quality and color of cottonseed flakes

Hull-free cottonseed flakes were prepared for direct solvent extraction by two passes through a pilot plant size, hot air drier set at 200 F. Moisture content was reduced to 6.5% without evidence of gossypol binding. Improved drainage characteristics resulted in better extraction. Glanded and glandless flakes which had been extracted and partially desolventized at low temperatures were heated indirectly in a batch desolventizer under vacuum to temperatures above the point of steam condensation and solvent stripped with superheated steam. Resulting available lysine and protein solubility values on the meals and flours were desirably high. The desolventization was accomplished without significant color darkening. Operated by the Texas Engineering Experiment Station for the Cotton Research Committee of Texas.     

Biological vs. Chemical evaluation of toxicity and protein quality of cottonseed meals

Summary 1. Toxicological evaluation of 68 cottonseed meals in rats failed to show a direct correlation between their toxicity and their free, total or combined gossypol content. The common practice of considering the free gossypol content of cottonseed meal as a yardstick for its toxicity is questioned. 2. There was poor correlation between biologically evaluated protein quality of cottonseed meals and their nitrogen solubility in 0.02N sodium hydroxide. Application of this chemical test for indicating the protein quality of cottonseed meals is likewise questioned on the basis of existing evidence. Presented at the Conference on Cottonseed Meal Quality as Related to Processing, Southern Regional Research Laboratory, New Orleans, La., January 24–25, 1955.     

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 oilseeds to meal and protein flakes

The prime consideration during processing of oilseeds to meals and flakes, i.e. toasting or cooking, is the time-temperature-moisture content relationship. Protein dispersibility decrease of any of these variables, but there is a threshold value for each variable below which the denaturation rate is very slow. In general, denaturation of protein is measured by its water dispersibility, i.e., denaturation increases as protein water solubility decreases. Choice of the extraction process for oilseeds depends primarily on the oil content of the seed and the allowable protein denaturation during preparation for extraction. Seeds with oil contents up to 30% may be extracted directly in percolation extractors, with minimum protein denaturation. Higher oil content seeds must be prepressed with some denaturation or they can be extracted by an immersion process such as centrifuge battery to minimize protein denaturation. The desolventizing operation is the most critical in fixing the degree of protein denaturation, since all three pertinent variables are near or above their threshold values. The selection of the proper processing units to desolventize completely the meal but maintain desired limits will be discussed. Subsequent heat treatment after the desolventizing process may be used to denature the protein or may be minimized to prevent much further denaturation. Prompt cooling is necessary before storage to preserve the required protein denaturation values. Classification and sizing may be required to meet the meal specifications. Presented at the AOCS-AACC Short Course on “Oilseed Proteins: Chemistry, Technology and Economics. French Lick, Indiana, July 1969.     

Lysine,gossypol, and nitrogen solubility in chemically treated cottonseed meals

The effects of treatment of commercial prepress-solvent extracted and direct-solvent extracted cottonseed mares with several chemical agents and solvents were studied. The analytical results for “free” and “total” gossypol of the finished meals show that treatment with aliphatic amines, followed by extraction with a suitable solvent, removed large proportions of the “free” as well as “bound” gossypol. This reduction of “free” and “bound” gossypol was accompanied, in some experiments, by an increase in the nitrogen solubility and available lysine, as compared with the results obtained with the untreated air-dried marcs. The available lysine contents of the treated mares was significnatly correlated with the nitrogen solubility in 0.02N aqueous NaOH. One of the laboratories of the Southern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture.     

Preliminary report on the nutritional significance of bound gossypol in cottonseed meal

Summary A procedure is described by which bound or inactivated gossypol can be removed from cottonseed meal without the application of heat which might damage the protein. The removal of bound gossypol increased the nutritional value of the protein as determined by chick feeding tests, rat protein-repletion tests, and lysine availability tests. A procedure is described for the preparation of a gossypol-cottonseed protein complex without heating the materials. As a result of the combination of the protein with gossypol, marked reduction in nutritional value occurred. The nitrogen solubility of the complex was only about half that of the original protein. The results are in accord with the concept that the inactivation of gossypol during the processing of cottonseed meal is accomplished through the formation of an insoluble, inert gossypol-protein complex which results not only in rendering the gossypol harmless but also in the loss of part of the nutritional value of the protein.     

Refining normal and genetically enhanced soybean oils obtained by various extraction methods

Four different extraction methods, extrusion-expelling, conventional flaking-solvent extraction, expander-solvent extraction, and screw pressing, were used to separate oil and meal of a commodity soybean. The quality and refining characteristics of oils obtained by these methods were evaluated, and the effects of extraction method on oil quality were determined. The screw-pressed oil was more oxidized and hydrolyzed than the oils from the other extraction methods. The extruded-expelled oil had oxidative status similar to the solvent-extracted oils, although it contained the lowest amount of tocopherols. Five genetically enhanced soybeans were also processed by extrusion-expelling and solvent extraction methods, and differences in refining of these oils were examined. Overall, extruded-expelled oils were significantly different from the solvent-extracted oils in that they contained less tocopherols and were more oxidized than the solvent-extracted oils during refining. The differences between oils from the two extraction methods were magnified owing to the inclusion in the experiment of oils with modified compositions. The more unsaturated oils underwent significantly more oxidative degradation during refining than did the more saturated ones.     

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.     

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.     

Survey of soybean oil and meal qualities produced by different processes

Soybean oil and meal produced by extruding-expelling (E-E) are believed to have unique characteristics compared with products produced by solvent extraction (SE). A survey was conducted to compare quality characteristics of the oils and meals produced from different types of soybean processing methods. Soybean oil and meal samples were collected three different times within a 1-yr period from 13 E-E mills, 8 SE plants, and 1 continuous screwpress (SP) plant. Properties of oil and meal varied considerably between different types of plants and among plants of the same type and sampling times. In general, settled crude E-E and SP oils had significantly greater peroxide values than those of SE oils. E-E oils contained less free fatty acid and phosphorus than did SE and SP oils. The oxidative stability (AOM) of E-E oil was less than that of SE oil, and that of SP oil was intermediate. E-E and SP meals had higher oil and lower protein and moisture contents than those of SE meals. Protein dispersibility indices were lower for E-E and SP meals. Protein solubilities in KOH were similar for E-E and SE meal, but higher than that of SP meal (62%). Rumen bypass protein values were higher for the SP meal.     

Improved method for determining gossypol in crude cottonseed oils

Summary The p-anisidine method for the determination of gossypol in crude cottonseed oils has been reinvestigated and modified to make it applicable to all crude oils obtained by the newer methods of processing cottonseed. The modifications included a change in the composition of the solvent, a higher reaction temperature, and the use of a more concentrated panisidine reagent. The modified method was found satisfactory where different colorimeters and spectrophotometers were used for measuring the color developed. Comparison of aniline and p-anisidine as reagents for the analysis of gossypol pigments showed that the presence of modified gossypol in some crude oils resulted in an over-correction for background absorption and led to significant errors when aniline was used as the color development agent. One of the laboratories of the Southern Utilization Research Branch, Agricultural Research Service, U. S. Department of Agriculture.     

Acidic ethanol extraction of cottonseed

Ethanol (EtOH) is being evaluated as an alternate solvent to hexane for the extraction of glanded cottonseed. Hot EtOH, needed for efficient oil and aflatoxin extraction, binds gossypol to protein. However, this binding can be minimized by acidifying aqueous EtOH with a tribasic acid, such as phosphoric or citric. While this solvent extracts oil and gossypol, it does not affect EtOH’s ability to extract aflatoxin. The defatted cottonseed meals produced from this process contained 0.03% total gossypol (which is lower than meal prepared by most other processes) and the aflatoxin content was reduced from 69 to 2.9 ppb. These are preliminary results and additional research is needed to determine commercial feasibility. The removal of essentially all gossypol from an extracted meal has the potential to expand the use of cottonseed meal as a feed, increasing its value to both the cotton farmer and the seed processor. Presented in part at the 40th Oilseed Processing Clinic, March 4, 1991, New Orleans, LA.