M. S. Kuk

Ethanol extraction of oil, gossypol and aflatoxin from cottonseed

Commercial processing of cottonseed requires hexane to extract and recover edible oil. Gossypol and aflatoxin are not removed from extracted meals. A bench-top extraction process with 95% (vol/vol) aqueous ethanol (EtOH) solvent has been developed that extracts all three of the above materials with a much less volatile solvent. In this process, cottonseed is pretreated and extracted with ambient 95% EtOH to remove gossypol and then extracted with hot 95% EtOH to extract oil and aflatoxin. Membranes and adsorption columns are used to purify the various extract streams, so that they can be recycled directly. A representative extracted meal contained a total gossypol content of 0.47% (a 70% reduction) and 3 ppb aflatoxin (a 95% reduction). Residual oil content was approximately 2%. Although the process is technically feasible, it is presently not economical unless a mill has a continual, serious aflatoxin contamination problem. However, if a plant cannot meet the hexane emission standards under the Clean Air Act of 1990, this process could provide a safer solvent that may expand the use and increase the value of cottonseed meal as a feed for nonruminants.

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.

Water accumulation in the alcohol extraction of cottonseed

The critical moisture content of cottonseed flakes extracted with an aqueous alcohol solvent can be defined as that flake moisture level at which the flakes lose no moisture during extraction. This study shows that the critical moisture content for aqueous ethanol (92%, w/w) is 3%. For aqueous isopropanol (88%, w/w) this value is 6%. If the moisture contents of the flakes are above these levels, then the solvents pick up moisture. For moisture contents below this level, the flakes adsorb moisture and actually dry the alcohol. It is proposed that this latter capability can be used as a basis for a method to control water accumulation in aqueous alcohol solvent extractions.

Ethanol vapor deactivation of gossypol in cottonseed meal

Most cottonseed cultivars contain gossypol, a polyphenolic antinutritional compound. “Free” gossypol is a physiologically active form of gossypol, which is toxic to young- and nonruminant animals. To utilize solvent-extracted cottonseed meal as a general feed, gossypol must be either removed or deactivated to a minimum level specified for each class of animal. Normally, deactivation is carried out prior to oil extraction; however, the desired level of deactivation is not always attained. A new supplemental method of deactivation has been found by using either ethanol or isopropanol vapors on solventextracted meal. In a bench-top set-up, ethanol vapor reduced free gossypol from 0.115 to 0.053%, and a further reduction to 0.026% has been observed with the addition of ferrous sulfate. The supplemental deactivation method can, in most cases, reduce free gossypol to significantly safer levels for feeding, thus increasing utility, and possibly demand, for cottonseed meal as a general animal feed protein source.

Process engineering economic evaluation of the ethanol extraction of cottonseed: Preliminary analysis

This preliminary analysis was undertaken to determine if the operations being developed for the aqueous ethanol extraction of cottonseed oil are economical and whether further research of this process should be pursued. Results of the conversion of hypothetical hexane extraction plants to ethanol extraction, in the plant capacity range of 300-600 tons of cottonseed flakes/day and operating 150-350 days annually, show that two unconventional operations, namely, chill-separation of miscella exiting the extractor and reduction of oil in recycled ethanol by reverse osmosis, require less energy and are less expensive than conventional alternatives. However, additional work is needed to determine the overall efficiency of an alcohol process as compared to a conventional hexane process.

Quick method for estimating free gossypol in cottonseed, meats, collets, and extracted meals

A method for estimating free gossypol (FG) has been developed that decreases sample-determination time from over 2 h to about 25 min per sample. With auto pipetters and bottle-to dispensers, six sample determinations can be completed in approximately 50 min. The method consisted of adding water and acetone separately to a fixed sample weight, mixing, filtering, diluting with 65% acetone, and reading absorbance on a spectrophotometer. Absorbance was plotted against the official American Oil Chemists’ Society’s FG method for samples that contained FG between 0.02 and 0.9%. Quadratic least squares regression for 31 samples had a correlation coefficient ofr2=0.986 and a standard error of estimated FG of 0.032%.

Adsorptive gossypol removal

Gossypol is extractable from cottonseed by using aqueous ethanol. The equilibrium between undissolved gossypol in cottonseed and that dissolved in the solvent determines the residual gossypol. To move the equilibrium toward extraction from the seeds, the dissolved gossypol needs to be removed from the gossypol-solvent-oil mixture. Gossypol removal from the mixture by adsorption on alumina, silica and molecular sieve 5Å was tested. Experimental results indicated that gossypol was more selectively adsorbed than triglycerides by these adsorbents. Alumina and silica had higher gossypol adsorption capacities than molecular sieve 5Å.