Connect With Us

Technology & Nutrient Quality Advantages of ExPress® Soybean Meal

Dave Albin, Ph.D. & Kenneth Aniunoh, Ph.D., P.E.
Insta-Pro International, 2023

About Us     |     Blog      |     What We Do     |     Contact

Soybeans are grown globally and traded around the world in large quantities, due to important agronomic characteristics, but more so, due to nutrient composition.  In particular, raw soybeans contain ample protein (35-40%) and oil (18-22%) and following conversion from this initial state into meal ingredient form, soy meal can be used in myriad animal diet formulations to supply key nutrients.  It is the amino acids that make up the protein, and the energy and essential fatty acids from the oil portion, that are the most useful to produce meat, milk, and eggs.

As early as 1930 in the US, 70% of soybeans were used as forages to feed ruminants, especially beef and dairy cattle¹. However, much has changed since then, with soybean acreage in the US having grown 20-fold by 2013, with the majority being used to produce meal and oil² for non-ruminant poultry, swine. It is widely understood that thermal processing and oil extraction were required to dramatically increase the use of soy meal in the field of animal nutrition.

This marked expansion of, and shift in, productivity followed the development of several methods to improve raw soybeans.  
When formulating diets for livestock and poultry used in the production of meat, milk, and eggs, the primary aim is to optimize the growth and performance of the livestock/poultry. A key aspect of this process is the production of quality feed with the required nutritional value, at the best possible cost. Soybean meal is a major source of protein and energy in feed formulations. These formulations greatly benefit from soybeans produced with an eye towards:

•    Deactivating anti-nutritional factors contained in soybeans.
•    Producing soybean meal with improved digestibility.
•    Provision of metabolizable energy without the need to add oils/fat from other sources.
•    Longer shelf-life of the soybean products (meal and oil).
•    Meal that is free of chemicals such as hexane.
•    Improved feed efficiency due to improved feed conversion rates.

The producers of such soybean meal will also have an eye towards the employment of processes and equipment that ensure:

•    Increased process efficiency
•    Low capital outlay for equipment

Insta-Pro’s ExPress® process for producing soybean meal is a process that provides all the above listed benefits by the pairing of two (2) unit operations, namely, mechanical oil pressing and extrusion cooking.  The ExPress® process achieves optimum efficiency by performing the extrusion cooking unit operation, upstream of the oil pressing unit operation.

 
Extrusion Cooking
In cooking, heat is used to prepare food for consumption. There are several reasons for cooking but at its core, cooking converts food into a more digestible form. This improved digestibility means that the calories and nutrients contained in the food are more easily absorbed by humans and animals. Cooking on an industrial scale requires cooking large quantities of food, in as little time as possible, while still maintaining high quality and adequate food safety standards. One method of achieving this is by applying extrusion technology to the field of cooking. 

Extrusion can be thought of as a continuous process for mixing and pumping material. When shear, heat, and pressure are thrown into the mix, the extruder can be used to cook the material. An extruder basically consists of a rotating screw housed within a barrel/compression chamber.  
 

References 

1. Feeds and Feeding, 20^th Edition, 1947. The Morrison Publishing Company, Ithaca, NY
2. USDA Coexistence Factsheets - Soybeans
3. Extruded Versus Raw Ground Soybeans for Dairy Cows in Early Lactation1 (journalofdairyscience.org)
4. Nutritional value of heat-treated soybean meal for channel catfish (Ictalurus punctatus) - ScienceDirect
5. PDF (usda.gov)
6. Deactivating antinutrients in oilseeds using different methods and temperature/time combinations – some notes on quality, consistent oilseed meals.  Insta-Pro International Research Report
7. Effect of hydrolysis time on the determination of amino acids in samples of soybean products with ion-exchange chromatography or precolumn derivatization with phenyl isothiocyanate - PubMed (nih.gov)
8. (PDF) Development of a novel bioassay for determining the available Lys contents of foods and feedstuffs (researchgate.net)
9. Effects of extrusion and expelling on the nutritional quality of conventional and Kunitz trypsin inhibitor-free soybeans - PubMed (nih.gov)
10. Growth performance of male broilers fed ExPress® soybean meal and high-shear dry extruded corn - ScienceDirect
11. 162 Digestibility of energy and nutrients and concentration of metabolizable energy in soybean expellers and soybean meal fed to growing pigs | Journal of Animal Science | Oxford Academic (oup.com)
12. Benz et al., 2007.  Kansas State University Swine Day Report
13. Aldrich and Merchen, 1995. University of Illinois Thesis
14. Cumberland Valley Analytical Services, Multistep Evaluation of Various Feeds
15. Harvatine, 2018.  Pennsylvania State University Research Report
16. Extruded soybean meal increased feed intake and milk production in dairy cows - ScienceDirect
17. Bobeck, 2023.  Iowa State University Research Report

Figure 1. Single Screw Extruder

The flow of material through the extruder is usually restricted by placing a die at the discharge end of the extruder (see Figure 1). In some cases, other restrictive elements (such as steam locks) are also placed along the length of the extruder screw. These restrictions to flow act to increase the residence time, of the material, within the extruder and cause a pressure build-up along the length of the extruder. The pressure increases from the inlet to the discharge. Since materials naturally tend to flow “downhill” along a pressure gradient, the pressure build-up forces material to flow back towards the extruder inlet. On the other hand, the rotation of the extruder screw “drags” material from the inlet towards the outlet. The interplay between the forward “drag” flow and the backward pressure driven flow determines the net flow rate of material. To generate a net positive flow through the Extruder, the mechanical energy supplied to the screw shaft must be sufficient to overcome the backward pressure driven flow.

Extrusion cooking technology essentially combines extrusion and cooking in one unit operation. The heat for the cooking process can be supplied from external sources, by heating the extruder barrel or directly injecting steam into the barrel or generated in-situ by frictional/viscous dissipation of some or most of the mechanical power used for rotating the extruder screw. Insta-Pro Extruders are designed such that all the heat required for extrusion cooking is supplied via viscous dissipation of the mechanical energy supplied to the extruder screw. The advantage of this approach is that it eliminates the requirement for additional equipment and utilities needed for heat supply from external sources.

Some key advantages of extrusion cooking include:

• It is a continuous process and thus lends itself to high throughputs and automation.
• It is a versatile process that can be used for a wide variety of products by simply changing operating conditions and/or the screw configuration.
• The extruder is a relatively compact machine and therefore possesses a small footprint.
• It is a high temperature-short time (HTST) process.

Insta-Pro Extruders are designed to apply extrusion cooking as a High Temperature-Short Time (HTST) unit operation for the processing of soybeans into soybean meal and soy oil. The HTST nature of the process significantly reduces, up to 85%, of unwanted enzymes and anti-nutritional factors that reduce shelf life, cause off flavors, and reduce protein digestibility, while still maintaining the quality of key nutrients present in the soybean. Another advantage of extrusion cooking, as part of the ExPress® process, is that it helps break open the cell structure of the soybean thus providing access to the oil contained within. This in turn increases oil yields during mechanical pressing of the full-fat soy meal.

Mechanical Oil Pressing

While Super-critical Fluid Extraction (SFE) is finding increasing use in the extraction of oil from oilseeds, the two most common methods of extraction remain Mechanical Oil Pressing and Solvent Extraction. Both methods (Oil Pressing and Solvent Extraction), rely on providing a gradient of some sort that encourages the expulsion of the oil contained within the oilseed. Solvent extraction uses a solvent, such as Hexane, to create a concentration gradient (between the seed material and the solvent) that drives oil from within the seed into the solvent. Instead of a concentration gradient, Mechanical Pressing employs a pressure gradient to expel oil from the seed (see Figure 2). A major advantage of the Oil Pressing method, over solvent extraction, is that Oil Pressing is a completely chemical free process.

Figure 2. Driving force for mass transfer in oil extraction

The Oil Press consists of a rotating screw contained within a cage/barrel (see Figure 3). The screw works to convey extruded soybean meal or full fat soy (FFS) from the Oil Press inlet to the outlet, while applying pressure to the meal. The cage/barrel has small holes that allow oil to pass through while keeping the solid residual material confined within the cage/barrel. 

Figure 3. Mechanical Oil Press

The amount of oil expressed from the soybean meal depends on the oil concentration within the soybean and the magnitude of the pressure gradient. The lower the oil concentration, the higher the pressure gradient required. Hence, Oil Presses are designed such that the size of the gap between the screw and the cage/barrel gets progressively smaller as material is conveyed from the inlet of the Oil Press to the outlet. This ensures that the pressure gradient applied to the extruded soybean meal increases as the material moves from the inlet to the discharge side of the Oil Press. 

The efficiency of the oil extraction is improved by pairing the Oil Press with an Extruder placed upstream of the Oil Press. A key advantage of the ExPress® process over solvent extraction is that the final pressed cake exiting the Oil Press contains about 6% – 8% residual oil. For solvent extracted soybean meal, the residual oil/fat levels are at less than 2%. Thus oil/fat needs to be added back into the solvent extracted meal to make up the required levels of metabolizable energy. This is not necessary with soybean meal produced using the ExPress® process as the process produces soybean meal that inherently contains the desired levels of oil/fat. 

The excess oil removed in the Oil Press can be further refined and used as cooking oil for frying or as feed for a biodiesel plant. The ExPress® process also produces high quality oil. 

It is known from laboratory testing and animal feeding trials that soy meals vary in quality, and that at least part of these quality differences are due to the processing method.  This is true for all modern, highly productive animals.  For example, when lactating dairy cows were fed balanced diets with identical amounts of soy, either raw or extruded (with the oil remaining in the meal, or “full fat”), milk production was similar, but numerically greater with extruded soy.  However, the cows fed raw soybeans exhibited reduced body weights by over 20 kg, while those fed extruded soybeans gained over 40 kg body weight, during the study period³.  Thus, extrusion clearly increased the amounts of nutrients available for use by the dairy cow, and in this case, extruded soy could have been fed at lower levels in the formulation.

In part, the benefits from thermal processing result from the decline in levels of naturally occurring antinutrients, which are potent defense mechanisms for soybeans (and most plants) that hinder nutrient digestion.  Often, an increase in thermal processing time is used to deactivate antinutrients, such as trypsin inhibitors, a common type⁴.  This is true of the commodity, hexane process⁵.  While this approach successfully reduced antinutrients in soy meal, data from this publication⁵ was used to determine that the longer heating times required for antinutrient reduction caused a major increase in the variation of remaining antinutrients, even as processing temperature variation, and the ranges used, were very consistent⁶.

Not only does prolonged heating times increase the variation of remaining antinutrients in soy meal, but nutrient damage can occur with heating.  This is especially true for the amino acids in protein, which degrade at different rates for different amino acids⁷.  With some methods of pressure cooking, lysine damage can occur in a few minutes⁸. 

Mechanical methods of soy processing usually limit cook time, which helps to preserve the amino acids in soy meal.  Often, these methods increase cook temperature to properly process raw soybeans.  High-shear dry extrusion (extrusion cooking), as part of the ExPress® process, limits cook time to about 20 seconds, and uses a temperature gradient throughout the extruder barrel so that the highest temperature is experienced at the outlet for only a few seconds.  

As a result, increasing the extruder temperature with the ExPress® process has been shown to increase amino acid digestibility and metabolizable energy, both indicators of nutrient quality, in poultry⁹.  Amino acid digestibility and metabolizable energy are indicators of how useful these nutrients are for productive purposes, like growth.  In addition, growth performance trials, which measure feed intake, body weight gain, and feed conversion ratio (efficiency) has shown that broilers fed soy meal from the ExPress® process exhibited greater body weight gain and feed conversion ratio compared to those fed commodity, solvent-extracted soybean meal, even though feed intake was unchanged¹⁰.  With swine, benefits of the ExPress® process have also been reported, but the mechanisms may be somewhat different.  While ExPress® soy meal – fed swine demonstrated greater amino acid digestibility and metabolizable energy than those fed commodity, solvent-extracted soybean meal¹¹, pigs fed ExPress® soy meal had similar body weight gains, but reduced feed intake and better feed conversion ratios¹².

The ability to operate at high-shear dry extrusion conditions of elevated temperatures for short periods of time also has benefits for ruminants, especially dairy cattle.  The ruminant digestive system contains a rumen, which is a microbial fermentation vat that alters everything the animal consumes.  Strategies for supplying nutrients for dairy cattle often involve the creation of ingredients that are protected from the effects of the rumen microbes.  Rumen bypass, or escape, proteins are used to achieve this feeding goal.  ExPress® soy meal contains ample rumen by-pass protein that remains highly digestible to the animal¹³ – once again, this is due to the nature of the process for soy.  While ExPress® soy meal maintains highly digestible amino acids after exiting the rumen, other by-pass soy meals exhibit lower digestibility values¹⁴.  In addition, recent university research has shown that the ExPress® process generates ample rumen bypass fat from the residual oil within the meal¹⁵.  These benefits translate into improved milk production, feed efficiency, and a greater amount of milk components compared to commodity, solvent-extracted soybean meal¹⁶.

It's also of interest to note that soy oils isolated with these different processes contain differences as well¹⁷.  Recent research with broilers indicated that ExPress® soy oil allowed for a significantly greater feed conversion ratio compared to birds fed another mechanical soy oil and commodity, solvent-extracted soy oil despite all oils having very similar compositions.

 Summarized in the Table below are key differences between soy meals produced with different methods of thermal processing.