SOYBEAN PROCESSING FOR FOOD PRODUCTION
(By: Dr. Wilmot
Wijeratne)
Insta-Pro
International, Des
Moines, Iowa, U.S.A.
Introduction:
Soybean has been produced and consumed directly as human food in the Orient for centuries. It is a storehouse of edible oil (approximately 18%) and protein (approximately 38%), both having economic and nutritional significance. It is only during the past half century that this crop has been exploited in the west under extensive production and processing practices. Today, soybean is the world’s leading source of edible oil and vegetable protein. Although phenomenal increases in soybean production have been achieved on a global basis, it is estimated that less than 10% of the world soybean crop is utilized directly in human food. Most of this fraction is accounted for by traditional whole soybean foods consumed in the Orient. A smaller portion is accounted for by soy flour, soy protein concentrates and soy protein isolates that are used as functional ingredients in mean, dairy, confectionery, and bakery products. Bulk of the world soybean crop is extracted for edible oil and the protein meal is used in animal feeds.
Opportunities:
Nutrition: The developing world, home for over 75% of the world population, is facing shortages in dietary protein and calories. Food legumes such as dry beans and lentils provide a significant contribution to the available food supply, particularly dietary protein. However, on a global basis, the production of these traditional food legumes stagnates at about 35 million metric tons, while the production of soybean is over 130 million metric tons. This provides an ideal situation to exploit the soybean for direct human consumption, and thereby, to alleviate food and nutritional deficiencies to a great extent.
Functionality: Soy protein has unique functional characteristics. Among them are emulsification, stabilization, water absorption and retention, texture formation, adhesion, cohesion and dough enhancement. Soy proteins are used in food systems such as meat products, bakery products, confectionery, pasta products and frozen desserts to take advantage of these functional properties. However, the levels of inclusion are quite low, and consequently, the total volume of use is limited. Soybean oil finds multiple uses in cooking oils, salad oils, margarine, shortening, salad dressings, mayonnaise and spreads.
Human Health: A wealth of new scientific knowledge has accumulated in recent times that point to the health-giving properties of soybean. There is convincing evidence on the effect of soy protein on lowering blood cholesterol, particularly in individuals having higher than normal cholesterol levels. Soybean phytochemicals such as the isoflavones have been associated with anti—carcinogenic activity. Soybean has also been associated with promoting bone health and alleviating post-menopausal discomfort in women. The Food and Drug Administration of the United State has approved a health claim for soy protein based on its ability to reduce cholesterol levels. These developments present an opportunity to spread the use of soy foods to the affluent and health conscious groups of populations.
Constraints:
Traditional soybean foods of the Orient have not found extensive markets outside that region. Considerable progress has been made in research and developments to introduce soybean foods into the diet of populations outside the Orient. Although some success stories are to be found, there are several important constraints against rapid expansion in direct human consumption of soybean: a) Soybean is well known for its propensity to develop so called “beany” or “painty” flavors, b) Unlike traditional food legumes, soybean takes a much longer cooking time, c) Soybean carries the general connotation of a product for animal feed rather than human food, d) Soybean contains anti-nutritional factors such as trypsin inhibitors at higher concentrations than found in food legumes. They must be inactivated by proper heat treatment before consumption.
Soy Food Products and Processing Technology:
Two broad categories of soy products can be recognized: 1) Oriental soybean foods, 2) soy protein products from solvent extraction.
Oriental Soybean Foods: Oriental soybean foods fall into two categories, namely, fermented and non-fermented. The fermented foods include Soy Sauce, Miso, Natto, Tempeh and Kinako. Each of these has characteristic flavors developed by the action of specific microorganisms responsible for the fermentation. Soy sauce finds wide acceptance as a condiment and flavoring. Miso, Natto and Kinako are characteristic of Japanese cusine. Tempeh is indigenous to Indonesia. The non-fermented oriental foods include Tofu, Soymilk, Yuba, green soybean (Edamame) and Soy Sprouts. Soymilk and Tofu consumption is gaining momentum outside the Orient. The rate of growth in the United States is about 15% per year.
Oriental soymilk is characterized by varying degrees of “beany” flavor, which is objectionable to many populations. Many advances have been made in developing new processes for soymilk production. The new processes minimize the beany flavor. Products having very acceptable flavor are now available in the market place. Tofu is widely consumed in the Far East, notably in China, Indonesia, Japan, Vietnam and Korea. It is a soy protein gel formed by adding coagulating agents to a water extract of soybean. This product comes in various textures and has the potential to extend or replace soft cheese products that are popular in many parts of the developing world. The main problem affecting the widespread use of tofu and soymilk is the fact that they are perishable products just like dairy products. In many parts of the world where refrigeration in storage, transport and retailing is not well developed, the product must be made and sold the same day. Soymilk and tofu are wet products having high moisture content and relatively low concentrations of the nutrients. For example, the average protein contents of tofu and soymilk have been reported as 6% and 2.5% respectively.
Products from Solvent Extraction: Solvent extraction is the leading technology used in processing soybean. This is a process in which soybeans are conditioned and brought in direct contact with an organic solvent, commonly n-hexane. The solvent dissolves the oil, leaving the protein-rich meal. The two fractions are then made free of the solvent to recover oil and meal.
Soybean oil finds its way into the edible oil market together with other vegetable oils. While much of the protein meal is fed to animals, a small portion gets further refined into protein products of human food grade. When protein meal is intended for human food use, the extraction process is carried out with food grade solvent. Removal of the solvent from the meal is carried out under low temperature to retain the functional properties of the protein. Under these conditions, edible grade defatted soy flour with approximately 50% protein is produced. This material contains all of the soybean components except the oil. Separating the water-soluble fraction of defatted soy flour produces a protein product of approximately 70% protein by extraction with alcohol or acid in aqueous medium. These products are called protein concentrates. Further processing to separate both the soluble and insoluble fractions from defatted soy flour results in soy protein isolates containing approximately 90% protein. A large number of commercial products with a variety of functional characteristics are available for specific applications.
New Technology:
Solvent extraction and further processing or protein meal is a large-scale and centralized industry. It involves heavy capital investment, large volumes of soybean, and well-developed infrastructure for storage and distribution. The solvent extraction industry is also facing environmental constraints related to the emission of solvent into the atmosphere. The negative effect of using chemicals in food processing is becoming a consumer issue. More importantly, there is widespread interest in value adding to the soybean at the rural level and small enterprise level in order to generate income and employment.
The Process: The industry has responded to this need by developing an alternative technology addressing the constraints facing solvent extraction. The new processing concept was developed at the University of Illinois in the United States. It is based on extrusion cooking of soybean followed by continuous screw pressing. Extrusion cooking is carried out in single screw dry extruder in which heat is generated by internal friction. The soybean is fed into the system at normal field moisture content. Inside the extruder, the material undergoes friction, shear and pressure, thereby developing temperature as high as 160˚ C. The total heating process is accomplished in an average residence time of less than 30 seconds. The extrusion cooking process inactivates anti-nutritional factors, stabilizes the material against off flavor development, reduces the microbial load and develops desirable flavor. Extrusion also results in the rupture of the cellular structure and release of oil into the cooked matrix. The oil is now in a very “free” state and it is very easy to press it out in the screw press. The process is made continuous by combining the extruder with a screw press of comparable throughput rate. The process results in the production of oil and partially defatted meal.
Product Quality: If the soybean is dehulled before processing, the processed protein meal contains about 50% protein and 6% oil. The meal can be easily milled into fine flour using conventional milling systems. The processing parameters can be controlled to obtain desirable functional characteristics in the protein meal, such as protein dispersibility, water/fat absorption and retention. Soy flour produced by this process has been used in the fortification of many food products at various inclusion rates without perceptible changes in the physical, chemical and functional properties; Viz. White bread (12%), Sugar cookies (24%), French bread (15%), Flat bread (25%), Doughnuts (12%), Cakes (25%), Muffins (20%). This flour has also been used to fortify many flour-based indigenous food preparations of Asia, Africa, and the Middle East. Soy flour of relatively high protein solubility can be produced by careful control of the process. Such flour having residual oil content of up to 8% has been further processed into textured soy products for use as meat extender or meat replacements.
Soybean oil produced by the new process has unique characteristics as well. The oil is brilliantly clear and has a light golden yellow color due to naturally occurring carotenoid pigments. The total phosphatide (gum) content is less than 0.2% compared to 1.5 – 2.0% in the case of solvent extracted crude soybean oil. Therefore, this oil is consumed without further processing markets where the natural color is not objectionable. If the color is objectionable, the oil may be physically refined without using caustic for neutralizing. Furthermore, the oil contains about 1,800 PPM of total tocopherols, which are biologically active as sources of Vitamin-E. They are also chemically active as antioxidants. Hence, the oil has good shelf stability without addition of antioxidants.
Commercialization: Complete plants for Extrusion Expelling are being marketed by Insta-Pro International under the trade name “ExPress™” system. Plants of installed capacities varying from 6-100 Tons/Day are being operated around the world, providing opportunity for value adding to soybean at the small scale level. The same process has also been adapted to process other oilseeds such as Cottonseed, Rapeseed and Sunflower seed. Small-scale oil refining systems to match the capacity of Extrusion/Expelling plants are also available to integrate the whole process and maximize value addition.
More
Information:
Soy Innovations
International
10104 Douglas Avenue
Des Moines, Iowa
50322, U.S.A.
Phone:
(800)779-7523
Email:
info@soyinnovations.com