Soybeans are considered the most important crop in the world with China recognizing their value for over 3000 years. Although the crop was only introduced to North America in 1804, the United States is now the leading producer and exporter of soybeans followed by Brazil, China and Argentina.
It is known that raw soybeans contain anti-nutritional factors that must be de-activated by heat treatment in order to make the soybeans suitable for consumption by humans and monogastric livestock.
The majority of soybeans are currently processed by solvent extraction to remove about 99% of the oil content. Soybean meal, the by-product of the process, is included in the diets of most food animal species. The majority of soybean meal produced is consumed by poultry followed by the swine, beef, dairy, pet food and aquaculture industries. Protein derived from soybeans is further processed to derive specialty products such as soy concentrate and soy isolates used for industrial, food and neutraceutical applications.
An alternative to extraction
Although solvent extraction is an efficient method to extract oil from soybeans, it requires considerable capital investment, a high level of technology and large scale operation. Hexane solvent is highly flammable, is considered a carcinogen and represents an environmental hazard. These constraints have forced the soy-industry to develop an alternative process that is less hazardous.
The emerging demand for identity preservation is incompatible with the current infrastructure of solvent extraction plants which are not in a position to segregate specific products. Organic certified consignments cannot be subjected to hexane extraction and extrusion is an ideal alternative to a solvent process.
Since the early 1960s, local farmers, cooperatives, and some sectors of the feed industry in the U.S. in addition to some 100 countries worldwide have recognized the extrusion technology of Insta-Pro as a method of adding value to soybeans. The high shear extrusion process allows flexibility in tailoring plant design to the exact need to achieve cost-effective conversion of beans to saleable product.
The fact that the process does not require a high level of technology, is effectively “all natural” and does not emit any undesirable residue into the environment has facilitated adoption of extrusion worldwide. Currently extrusion plants can be configured to simultaneously produce full-fat soy, partially de-fatted soybean meal (ExPress soybean meal), and chemical-free, virgin soy oil.
Probably the most important factor in the successful adoption of this technology is the fact that the nutritional superiority of full-fat soy or ExPress soybean meal has been documented by independent universities worldwide, private sector and end users.
High shear extrusion
High shear extrusion refers to the fact that this type of extruder does not require an external source of heat or steam. Heat is generated through friction as the sole source of energy to “cook” and partially dehydrate soybeans within seconds.
As the extrudate (processed material) exits the barrel of the extruder, cells are ruptured resulting in the release of tocopherols (natural anti-oxidants). The process enhances the availability of oil, de-activates the anti-nutritional factors such as trypsin inhibitors, lectins, urease, lipase and lipoxyginase enzymes. This creates a highly digestible source of energy and protein for all animal species, especially poultry and swine.
Extruded soy products options
Extruded whole soybeans contain on average 38% protein and 18% oil. The product can be processed by Insta-Pro extruders selected to conform to required daily capacity. The extruder can be fitted with a steam pre-conditioner to almost double the capacity of a given Insta-Pro model extruder without affecting quality of full-fat soy. The only difference would be that applying steam allows an increase in the moisture content of full-fat soy to about 10% compared with 5% to 6% without a pre-conditioner.
To produce ExPress soybean meal, the extruded full-fat soy is channeled from the extruder to an Insta-Pro horizontal press (expeller) in which up to 75% of the oil can be removed from the extruded full-fat. The resulting ExPress soybean meal will average 46% protein and 6% to 8% oil.
ExPress soybean meal with higher protein content can be produced if the raw soybeans are dehulled. In this case, the ExPress soybean meal may contain 48% to 50% protein and 6% to 8% oil. The ExPress system does not permit the use of steam pre-conditioning since the moisture interferes with the expulsion of oil.
The extruded-expelled oil that is produced has unique characteristics in terms of stability and low levels of phosphatides, unsaponifiable matter, peroxide value and free fatty acids. Insta-Pro installations therefore provide the capability to refine oil through a physical process without using chemicals.
Table 1 shows the typical composition of Insta-Pro extruded soy products compared with conventional soybean meal and full-fat soy processed by alternative procedures.
The main advantage from extrusion, as shown in the comparison is the higher metabolizable energy and dry matter content of Dry Extruded Whole soybeans or DEW (full-fat beans processed by Insta-Pro extrusion) compared to conventional full-fat soybeans processed by alternative methods.
ExPress soybean meals with or without the hulls removed have similar nutrient profiles to corresponding conventional solvent-extracted soybean meals. Again, the major difference is that the ExPress soy meals are superior to the solvent-extracted soybean meal on the basis of higher fat, metabolizable energy and dry matter content.
Higher energy and dry matter allows for greater flexibility in feed formulation. Extruded products which contain oil, add fat to poultry and swine diets without the problems associated with conventional methods of supplementation. These include more predictable quality of fat, improved flowability associated with the extruded soybean products, longer shelf life due to the presence of natural Tocopherols antioxidants and less dust.
Local processing of soybeans permits direct control of quality and predictability of performance. A disadvantage of commercial expressing systems is the lack of standardization of the product. Soybeans vary among growing areas and seasons. Insta-Pro provides both equipment and training to optimize the value of extruded products. It is however the responsibility of the nutritionist to determine the quality and nutrient content of an extruded product at any given location. Variations in the quality of expressed soybean meals may be due to producers adding water back to the express meal to compensate for dehydration losses during extrusion thereby depressing the nutrient content below tabular values.
Quality control, quality assurances
To produce high-quality extruded full-fat or ExPress soybean meal and oil, Insta-Pro recommends using raw soybeans with low levels of contamination with foreign material. A 9% to 11% moisture content of the raw soybeans is preferred. An extrusion temperature of 310F to 320F (154C to 160C) is recommended, based on optimum digestibility of nutrients, metabolic studies and performance comparisons.
Quality indices for whole soybeans and optimally extruded ExPress soybean meal as shown in Table 2 are attainable.
The nutritional quality of soybean products is related to the method of processing. Full-fat soybeans from the Insta-Pro dry extrusion process provide highly digestible amino acids (92.5%) in cecectomized cockerels as compared with wet extrusion (85.6%), micronization (87.9%), and toasting (91.4%). Nitrogen retention by chickens fed full-fat soy processed from an Insta-Pro dry extruder is significantly higher than that achieved by feeding toasted, micronized, “jet-sploded,” wet extruded, solvent extracted soybean meal plus added oil or raw soybeans.
A UK manufacturer of Insta-Pro dry extrusion full fat soy conducted two feeding trials to compare the product with solvent extracted soybean meal in isocaloric and isonitrogenous diets. Feeding extruded full-fat product to commercial flocks resulted in higher weight gain (1.83 kg vs.1.79 kg) and better feed efficiency (2.07 vs. 2.18) for the extruded and control groups respectively. It was concluded that superior feed efficiency was attributed to the higher ME value of full-fat soy.
Iowa State and other universities conducted numerous trials feeding dry extruded full-fat soy to broilers. Incorporating extruded full-fat soy in diets resulted in higher daily gain and feed efficiency compared to solvent extracted soybean meal with added animal and vegetable fat.
Feeding broilers diets containing full-fat soy extruded by the Insta-Pro process resulted in significantly higher (p<0.05) weight gain and feed efficiency compared to wet extruded full-fat soy or roasted full-fat soy.
Replacement of soybean meal and added oil in broilers diet (1-48 days of age) with increments of either toasted or extruded full-fat soy is practical although high inclusion levels of toasted soybeans resulted in lower weight gain. Increasing the substitution level with extruded full-fat beans resulted in a numerical increase in weight gain and an improvement in feed conversion efficiency. This indicated more consistent quality of the extruded full-fat product compared to toasted full-fat soybeans.
Higher feed efficiency
Optimizing processing conditions is crucial to achieving maximum digestibility of protein, amino acids and metabolizable energy. This has been demonstrated by many investigators who reported an increase in true metabolizable energy (TME) and a linear increase in the amino acid digestibility of whole soybeans processed by an Insta-Pro extruder. The highest TME and amino acid digestibility was achieved at 309F (154C).
Dry extruded full-fat soy resulted in significantly higher egg production and feed efficiency (p<0.05) in commercial hens compared to feeding solvent extracted soybean meal, roasted full-fat soybeans or raw soybeans. In other trials it was reported that toasted soybeans had a urease activity of 1.24 pH rise, and protein solubility of 91.87% compared with 0.2pH rise urease activity and 87.71% protein solubility for soybean meal. Extruded soybeans showed urease activity of 0.01pH, with 83.98% protein solubility. It was concluded that extruded full-fat soybeans can partly or totally replace soybean meal in the diet as opposed to toasted soybeans.
A trial using weaning pigs showed a 26% reduction in fat digestibility when roasted soybeans were compared to extruded full fat soybean meal. Similar results were reported in a starter pig trial in which pigs were fed isocaloric isolysine diets comprising corn-SBM-whey and soybean oil compared to extruded or roasted full fat soybean meal derived from either regular-Kunitz or low-Kunitz soybeans. It was reported that pigs fed extruded full fat product grew significantly faster, ate more feed and were more feed efficient than pigs fed roasted full fat soybean meal.
The results of metabolic studies using SBM (45.1% protein), roasted full fat soybean meal and extruded full fat soybean meal demonstrated an ME value for extruded soybean meal of 4414 kCal/kg which was 25.6% higher than the 3514 kCal/kg value observed for roasted soybeans.
The swine ME value for extruded soybeans is 21.8% above the tabulated NRC value. In contrast the swine ME for roasted soybean meal was 3.1% lower than the NRC value. It is evident that the NRC tabular ME value of extruded beans should be sub-classified by the method of processing to reflect accurate values for roasted and extruded full fat soybean products respectively.
Extruded-expelled soybean meal
The University of Illinois collaborated with Insta-Pro International to investigate the possibility of using the dry extrusion process as a pre-treatment for separating oil from meal. It is known that dry extrusion results in the deactivation of the anti-nutritional factors and total rupturing of cells within seconds. In the case of soybeans, as the product exits the barrel of the extruder, the oil is reabsorbed into the meal, producing full-fat soy.
Combining the dry extruder with a horizontal press to immediately separate most of the oil produces high quality soybean meal that retains 6% to 8% oil. The process produces natural oil which is beneficial for countries that cannot afford the cost and technical complexity of solvent extraction.
Coarsely ground extruded soybeans immediately processed in a continuous screw press results in high quality oil and pressed cake. Extrusion prior to expelling greatly increased the throughput of the screw press beyond the rated capacity. On dry matter basis, the extruded-expelled cake contains 50% crude protein and 6% residual oil. Extrusion cooking results in 90% inactivation of trypsin inhibitors and the low-fat cake can be ground easily in a hammer mill. Rupturing of the cells during extrusion results in the release of natural tocopherols which contributes to improved stability.
Insta-Pro has commercialized the system under the trade name "ExPress System" and the extruded-expelled soybean meal is registered as "ExPress Soybean Meal."
Studies have defined the effect of extrusion temperature on TME and digestibility of amino acids for poultry (Table 3).
Kansas State University studied the apparent ileal digestibility of amino acids and the digestible and metabolizable energy content of dry extruded-expelled soybean meal in relation to growth of pigs. Results indicated significantly greater amino acid digestibility (Table 4). Digestible and metabolizable energy of extruded–expelled soybean meal (with or without the hulls removed) was compared to dehulled solvent extracted soybean meal (Table 5). No difference in digestibility was reported between dehulled or non-dehulled extruded expelled soybean meal (Table 6).
The InstaPro ExPress system has the flexibility of producing extruded full-fat, ExPress soybean meal and Expelled soy oil simultaneously. Other oil seeds such as cotton, canola and sunflower are processed with the ExPress system in the U.S. and abroad.