Solvent extraction of oilseeds

Dl.l Extraction and Measurement of Total Lipids Basic Protocol 1 Solvent Extraction of Oilseeds, Nutmeg, and Other Foods Dl.1.1... 

SOLVENT EXTRACTION OF OILSEEDS, NUTMEG, AND OTHER FOODS USING THE SOXHLET METHOD... 

The low temperature in solvent extraction of oilseeds should produce a better oil than oil from the high-temperamre environment of screw-pressing. Solvent, however, extracts some nontriglycerides that are not pressed out by screw-pressing, so screw-press oil is generally of better quality than solvent-extracted oil. Although some animal fats are solvent extracted, most renderers full-press in screw-presses. Solvent extraction of oilseeds, on the other hand, is widely practiced. The section below is based primarily on research conducted with oilseeds. Some of it, however, would also apply to extraction of animal fats. 

Luigi, Continuous Solvent Extraction of Oilseeds and Lecithin Production, Iwgi Express fofor-... 

Raw food. Traces of heavy metal ions are present in many enzymes and other metal-bound proteins. For example, during the crushing and solvent extraction of oilseeds, metal bonds dissociate and the free ions bind to fatty acids. 

A general flow sheet for direct solvent extraction of many row crop oilseeds is shown in Fig. 34.8. Initial quality of the seed, and its preparation for extraction, have the most effect on yield of extracted oil, subsequent required refinery operations, and yields of (saleable) neutral oil. Freshly harvested seed should be cleaned of trash, which may become ignited during drying, or harbor moisture that accelerates seed heating in storage. Oils of most good quality, dry, row crop... 

Solvent extraction. The press cake emerging from a screw press still retains 3 to 15 percent of residual oil. More complete extraction is done by solvent extraction of the residues obtained from mechanical pressing. The greater efficiency obtained in the solvent extraction process encouraged the industry for direct application to oilseeds. In the United States and Europe, continuous extractor units are used in which fresh seed flakes are added continuously and are subjected to a counterflow of solvent by which intimate contact is achieved between the seeds and solvent. The common solvent for edible oil is commercial hexane or heptane, commonly known as petroleum ethers, boiling in the range of 146 to 156°F (63.3 to 68.9°C). After extraction, maximum solvent recovery is necessary for economical operation. The solvent is recovered by distillation and is reused. The extraction oil is mixed with prepress oil for refining. The extracted meals contain less than 1 percent of residual oil. 

Alcohols as Solvents. As a result of environmental concerns and inability of hexane to extract gossypol and aflatoxin, recent research on the solvent extraction of cottonseed has centered on developing processes using ethanol and isopropanol. The use of these alcohols to extract cottonseed and many other oilseeds is not new. 

A combination of mechanical and solvent extraction is often applied to oilseeds with high oil content, e.g., sunflower, safflower, com germ, and canola. The most efficient method of extracting the oil is mechanically expelling about 60% of the oil and then using solvent extraction of the remaining oil. 

Solvent Extraction with Oilseeds—Extraction of the bleaching earths in a mixture with oilseeds is practiced by some extraction plants with processing capabilities, but the potential problems for this type of recovery may outweigh the savings for example, the mineral content of the meal may be increased beyond the acceptable limits, and the recovered oil may decrease the quality of the new oil extracted. The oxidation products and polymers from the recovered oil could contaminate the fresh oil. 

Palm kernel meal generally refers to the product obtained after solvent extraction of palm oil from the oil palm, whereas palm kernel cake is produced by mechanical extraction. In practice, the term palm kernel meal is often used to describe either product. This food has a comparatively low content of protein, and the balance of amino acids is poor. The first limiting amino acid is lysine. The ratio of calcium to phosphorus is more favourable than in many other oilseed residues. The meal is dry and gritty, especially the solvent-extracted product, and is not readily eaten it is therefore used in mixtures with more acceptable foods. Attempts to use it mixed with molasses, as molassed palm kernel cake, have not been successful. It has a reputation for increasing the fat content of milk, and its chief use is for dairy cows. Palm kernel meal has been described as being balanced for milk production, but in fact it contains too high a proportion of protein to energy. 

The overall extraction process is sometimes subdivided into two general categories according to the main mechanisms responsible for the dissolution stage (/) those operations that occur because of the solubiHty of the solute in or its miscibility with the solvent, eg, oilseed extraction, and (2) extractions where the solvent must react with a constituent of the soHd material in order to produce a compound soluble in the solvent, eg, the extraction of metals from metalliferous ores. In the former case the rate of extraction is most likely to be controUed by diffusion phenomena, but in the latter the kinetics of the reaction producing the solute may play a dominant role. 

The sohd can be contacted with the solvent in a number of different ways but traditionally that part of the solvent retained by the sohd is referred to as the underflow or holdup, whereas the sohd-free solute-laden solvent separated from the sohd after extraction is called the overflow. The holdup of bound hquor plays a vital role in the estimation of separation performance. In practice both static and dynamic holdup are measured in a process study, other parameters of importance being the relationship of holdup to drainage time and percolation rate. The results of such studies permit conclusions to be drawn about the feasibihty of extraction by percolation, the holdup of different bed heights of material prepared for extraction, and the relationship between solute content of the hquor and holdup. If the percolation rate is very low (in the case of oilseeds a minimum percolation rate of 3 x 10 m/s is normally required), extraction by immersion may be more effective. Percolation rate measurements and the methods of utilizing the data have been reported (8,9) these indicate that the effect of solute concentration on holdup plays an important part in determining the solute concentration in the hquor leaving the extractor. 

Solvent Extraction. Extraction processes, used for separating one substance from another, are commonly employed in the pharmaceutical and food processing industries. Oilseed extraction is the most widely used extraction process on the basis of tons processed. Extraction-grade hexane is the solvent used to extract soybeans, cottonseed, com, peanuts, and other oilseeds to produce edible oils and meal used for animal feed supplements. Tight specifications require a narrow distillation range to minimize solvent losses as well as an extremely low benzene content. The specification also has a composition requirement, which is very unusual for a hydrocarbon, where the different components of the solvent must be present within certain ranges (see Exthaction). 

Fig. 5. Flow diagram of the extraction of PHA from oilseeds using PHA organic solvents. The final products obtained from the plant, i.e., PHA, oil and meal, are indicated in bold...

Better and Davidsohn (23) reported that the susceptibility of proteins in oilseed presscaFe and solvent-extracted meal was strongly affected by heat treatment. Working with peanut and coconut presscake, they demonstrated that the stronger the heat treatment, the higher are the concentrations of pepsin required to make peptization more complete. This is an important fact to bear in mind when oilseed press or extraction residues are being used as raw materials for production of industrial protein. 

Extraction of fat by supercritical carbon dioxide was investigated as an important option for minimizing the expanded use of frequently flammable and carcinogenic solvents in food analysis. Unfortunately, the presence of moisture in foods has an adverse effect on the quantitative extraction of fat by supercritical fluid extraction (SEE). Hence, samples have to be lyophilized first. The total fat content of freeze-dried meat and oilseed samples was found to be comparable to values derived from Soxhlet-extracted samples (26). Besides, only small amounts of residual lipids could be recovered by an additional extraction of the SFE-extracted matrix by the Bligh and Dyer solvent extraction procedure. As far as the minor constituents are concerned, it was found that the extraction recovery ranged from 99% for PC to 88% for PA. Hence, Snyder et al. concluded that SFE can be used as a rapid, automated method to obtain total fat, including total phospholipids, from foods (26). 

Cottonseed is important in world oilseed production, major producing countries being the USA, China, India, Pakistan, Latin America and Europe, ft is the second most important protein feedstuff in the USA, produced mainly by solvent extraction. Most of the cottonseed meal is used in ruminant diets, but it can be used in poultry diets when its limitations are taken into account in feed formulation (Ravindran and Blair, 1992). 

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