Soybeans processing

Fig. 4. Schematic outline for processing soybeans into oil and meal by hexane extraction. Courtesy of Dravo Corporation.

Soybeans are the most important oilseed in international trade. The United States, Bra2il, and Argentina are the main suppHers to the export markets. In 1994—1995, United States exports of 22.0 x 10 metric tons represented 32% of the domestic production, 16% of the world crop, and 69% of the international trade in soybeans. The European Union, Japan, Mexico, and Taiwan were the largest importers of soybeans (51). Japan, which produces <5% of its soybean needs, is the largest single soybean customer of the United States. Japan imported 3.4 x 10 t in 1994 (51). The United States also exports processed soybean products, eg, oil and meal. For 1990—1993, an average of 47% of the crop was exported as whole beans and processed products. 

About 62 mills having an aimual capacity of 47 x 10 t process soybeans in the United States. These operate at an average of ca 80% of capacity... 

By 2006, the U.S. had 77 ethanol plants producing more than 3 billion gallons of ethanol per year. Canada produced an additional 60 million gallons. Corn was the feedstock in 62 of the 77 U.S. plants. Other feedstocks included seed corn, corn and barley, corn and beverage waste, brewery waste, cheese whey, corn and milo, corn and wheat starch, potato waste and various sugars. The U.S. had 11 additional plants under construction and 55 proposed. West Central Soy processes soybeans to a food grade oil. Alcohol and a catalyst are then used to produce biodiesel fuel and glycerin. 

In their raw, natural state, these oils exist in the form of a triglyceride or fat. In order to derive the useful oil from the raw material, the triglyceride must be separated from protein bodies and sterols also present within the oil seed. To illustrate this process, soybean oil production will be briefly described. 

FIGURE 12-5. Schematic for Processing Soybeans into Oil and Meal... 

The second major example of a process-induced chemical side reaction was the formation of dichiorovlnylcysteine. Diehloro-vinylcysteine was formed when soybean oil meal was extracted with trichloroethylene for the removal of the fat in the production of animal feedstuffs (39) (Table VIII). The symptoms were first observed in cattle fed the extracted meal. The cattle developed hemorrhagic symptoms and many died. This process was discontinued. Although the trichloroethylene-processed soybean meal was entirely designated for animal feed, there was the possibility that small amounts could have found their way into human... 

Zinc Bioavailability from Processed Soybean Products... 

The original soybean oil (SBO), the processed soybean oil under similar conditions without catalyst (SBO control), and polymers of soybean oil (PSBO) were dissolved in THF. Molecular weights and molecular weight distribution were measured by GPC with a differential refractive index detector using THF as an eluent. The flow rate was 1.00 mL/min at 40 C. The injection volume was 100 pL. Linear polystyrene standards (Polymer Laboratories (PL), Mn = 580-lOOK, Mw/Mn = 1) were used for calibration of molecular weights of all polymers of PSBO. 2 PL gel 3 pm mixed E columns (300 mm x 7.5 mm) in series were used to resolve the samples. 

Figure 6. Photograph inside a modem direct soivent-extraction piant processing soybeans (courtesy of Crown Iron Works, Minneapoiis, MN). (This figure is avaiiabie in fuii color at http //www.mrw.interscience.wiiey.com/biofp.)...

There has been much speculation about using supercritical carbon dioxide because using this technology eliminates safety issues as carbon dioxide is not flammable and the oil is better quality (139), but no such plants have been constructed to process soybeans. This is due to the absence of a commercially feasible means of continuously feeding soybean flakes into a high-pressure vessel and removing the spent flakes. Recently, one company has developed a screw press in which supercritical carbon dioxide is injected into the barrel. This equipment has been successfully used to produce soybean meal with lower residual oil contents than typically produced by screw pressing and with httle heat denaturation of the protein. 

Recently, polymeric ultrafiltration membranes were used for degumming crude soybean oil and removing phospholipids from the crude oil/hexane miscella (168). Crude soybean oil also can be de-acidified by methanol extraction of the free fatty acids and the extract separated into fatty acids and solvent by a membrane filter (169). A surfactant-aided membrane degumming also has been applied to crude soybean oil, and the degummed oil contained 20-58 ppm of phosphorus (170). Supercritical carbon dioxide extraction was shown to be an effective means of degumming (171). In this process, soybean oil countercurrently contacted supercritical carbon dioxide at 55 MPa and 75°C. The phosphorus content of the oil was reduced from 620 ppm to less than 5 ppm. Ultrasonic degumming was also successfully used to reduce the gum content of soybean oil (172). 

A. R. Baldwin, Processing Soybean Oil—Some Practical Considerations for Preserving Flavor Quality, Rroceedings, Regional Oil Conference, Tehran, Iran, Sponsored by Soybean Council of America, 1964, pp. 30-33. 

The author is developing (mid-2004) zero trans-, no hydrogenation, no interesterification, no modification of any kind, tub and stick margarines. The formula will include specially processed soybean oil, corn oil, cottonseed oil, or mid-oleic sunflower seed oil, and double-fractionated palm oil, or double-fractionated cottonseed oil. The products are proprietary for now. 

Main Objectives for Processing Soybeans with Extrusion... 

Whole soybeans contain not only high-quality protein (38 2%), but also a rich source of energy as a result of the oil they contain (18-22%). They have the potential of supplying major amounts of both energy and protein to all types of livestock and poultry feed. Collective terms that are being used to describe processed soybeans range from full-fat soybeans, heat-processed soybean seeds, heat-treated soybeans, to simply whole soybeans. More specific references are seldom used to correctly identify the processing method. 

The National Research Council (NRC) for poultry (17) used the collective term heat processed soybean seed. It reported an ME value of only 3300 kcal per kilogram (13.8 MJ/kg), which is not much different from that of raw soybeans listed above. No mention to the method of processing was made. 

Dry extmders can successfully process soybeans without the additional use of steam conditioning. This may be advantageous in terms of oil availability. However, the use of a steam conditioner in conjunction with dry extmders will increase throughput, improve inhibitor destraction, and enhance the biological value of the protein in the end product. 

There are mainly two types of wet extruders that are being used to process soybeans (1) segmented single-screw extruders and (2) interrupted flight extmders/ expanders. 

Extrusion-expelling concept is being used in the United States, Russia, and other countries to process soybeans and other oil seeds. Recently, extrusion-expelling technology has been adopted commercially by some soybean producers, grain elevators, entrepreneurs, and cooperatives in the United States and elsewhere... 

According to Watkins et al. (63), the use of an expander offers several advantages in processing soybeans for extraction. 

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