Oilseeds solvent extraction

Many workplace, environmental, food safety, and other regulations apply to oilseed and oil processors (55). Some of the regulations required in the United States are discussed. Many other countries have similar requirements, but if they do not, it would be prudent for oilseed solvent extraction operations and vegetable oil processors to consider meeting these regulations and for these industries to have environmental, health and safety, and quality management programs (135, 136). 

Some residual oil remains in the cake because the expeller cannot exhaust all the oil, hence less oil yield per given mass of oilseed. Solvent extraction is neither economic nor safe at this level. 

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). 

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. 

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... 

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). 

Continuous screw presses are used (1) for extracting fats and oils in small operations where investment capital or supplies of raw materials are limited and installation of a solvent extraction plant is impractical (2) to partially defat high-oil content seeds for easier handling in subsequent solvent extraction or hard pressing and (3) for extraction of animal flesh and bones, fish, and fleshy-type oilseeds such as palm fruit, olives, and copra (dried coconut meat ), and oilseeds. These machines have been generically referred to as expellers, but the Expeller trademark belongs to Anderson International Corporation, Cleveland, OH, successor to the company founded by Valerius D. Anderson who patented the first continuous screw press in 1899. 

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... 

Introduction of the expander, a high-shear extruder with an interrupted-flight screw, in the mid-1980s revolutionized oilseed extraction practices. Essentially all solvent-extracted cottonseed, and approximately 70 percent of domestic soybean tonnage now are processed... 

Introduction of the expander has enabled extraction plants to handle additional seed species, with purchase of only minimal cleaning and dehulling equipment where needed. Prepress-solvent extraction facilities are being replaced by expander-direct solvent extraction equipment, leaving two basic extraction processes in modern large volume oilseed extraction plants expander-direct solvent extraction, and hard press for applications... 

Hardly any batch-type oilseed solvent extractors remain. Three of the more popular types currently manufactured include (1) shallow bed-type extractors, where a 0.5-1.5 m thick layer of collets or flakes is pulled across a linear screen and extracted by drenching with a countercurrent flowing miscella consisting of solvent and solubilized oil (Fig. 34.13) (2) diffusion belt type, where deeper beds of collets or flakes are conveyed on a woven mesh or folding-pan belt while drenched in countercur-... 

Moore, H. N., Oilseed handling and preparation prior to solvent extraction, J. Am. Oil Chem. Soc., 60, 141A-144A (1983). 

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. 

Inventory Update Rule (lUR) (40 CFR 710). The lUR was established in 1986 to require manufacturers and importers of chemicals listed on the master TCSA Inventory to report current data every four years on the production volume of chemicals imported or produced. Food and feed products produced from natural agricultural product, such as oilseeds, are not required to be reported but all oU and meal products obtained by solvent extraction that is sold for other than food or feed use (e.g., oils as chemical raw materials and meal as fertilizer) are. Cottonseed oil, soap stocks, acidulated soap stocks, deodorized distillates, hydrogenated cottonseed oil are some of the substances reported by extraction and refining operations under lUR. EPA amended this rule in 2003 (1/9/03 68 FR 848). Cottonseed oil is on the list of partially exempt substances, which are not subject to the new reporting requirements for processing and use data but continue to have to report the current lUR information as well as manufacturing exposure-related information. 

Determining the oil content of safflower seed in the laboratory by solvent extraction is also more difficult than for other oilseeds because of the vast difference in texture of the hull compared to the kernel within. The hull must be cracked or all of the oil will not be extracted. But in cracking the seed, the kernel tends to mash as well and small amounts of oil can be lost in the process, a small amount is important when the sample contains only 5g of seed. Since many people expressed dissatisfaction in safflower oil content analyses, PVO s control laboratory worked for a long time to develop a better method than the standard AOCS procedure (136). This method of analysis is now part of the NIOP rules for safflower (137). 

The modem commercial methods of oil extraction from oilseeds include (1) batch hydraulic pressing Oil seeds are expressed by hydraulic pressure to yield oil (2) continuous mechanical pressing Oil seeds are squeezed through a tapering outlet and oil is expressed by the increasing pressure and (3) solvent extraction Oil seeds are extracted with solvent followed by removal of solvent to yield oil. These methods are also employed in the extraction of sesame seeds with some modification. 

Quality standards and trading rules for solvent-extracted soybean meal and oil are designated by the National Oilseed Processors Association and are available at a website (145). Soybean products are remarkably uniform in their quality characteristics compared with alternative sources of oil and meal. 

Mechanically Extracted Meals. Solvent extracted oilseed meals typically contain less than 1.5% residual fat unless the gums (hydrated phosphatides) or soapstock have been added back to the meal before the desolventizer-toaster or meal dryer. Mechanically extracted (expeller or screw-pressed) meals can contain 4—9% oil, which can be a significant calorie source in animal feeds. Fat contents of extracted meals are not part of the definition, although typical analyses are shown below. 

The major lecithin sold domestically in commercial quantities is extracted from soybeans. Com and sunflower seed lecithins are available in limited amounts. Canola is being reviewed as a lecithin source in countries that do not grow significant quantities of soybeans. Lecithins may be added to feeds in cmde or refined forms, remain as residuals in solvent- or mechanical-extracted oilseed meals, be returned to oilseed meals as extracted gums or soapstocks at combined solvent extraction-oil refinery operations, or simply be native to an oilseed fed whole. 

Cake or meal from oil extraction contains 40-50% protein when processed in a screw press and 56-60% protein after solvent extraction. Sesame products have a pleasant flavor and contain high levels of methionine and cysteine. The flour produced from sesame meal has a high nutritive value compared to other oilseed flours (75). 

Other options for recovery of oil from spent clay include mixing the spent clay filter cake with milled oilseeds en route to solvent extraction. This procedure is used in some refineries having associated crushing and refining plants and is convenient if the fire hazard of the spent clay can be overcome and the level of addition is small enough to not significantly alter the mineral content of the meal (99). 

Correct preparation is required for efficient crushing and for solvent extraction. Wherever possible, oilseeds should be dehulled before the oil is removed. This will increase the capacity of the processing equipment and avoid loss of oil that would otherwise be absorbed into the hulls. Oilseeds should be flaked, rolled, or ground, and dried to optimum moisture and temperature. Some oilseeds, especially those low in fiber or high in protein, should be cooked at elevated moisture for 15-20 minutes (to harden the protein) and then dried. Cooking and drying also ruptures the oil cells and reduces oil viscosity. This allows the oil to more easily drift from the solids and be extracted by the solvent. 

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