When prepared correctly, plants are a nutritional and low-cost source of protein for animal feed. The soybean is especially valuable as a food source because of its high protein content and favorable amino acid profile. However, soy also contains several enzymes that can negatively impact nutrition and potentially harm animals and humans.
Cooking and drying the seed is required during processing to destroy the anti-nutritional factors. However, to retain the nutritional benefits of soy, processors need to fine-tune the time and temperature of heat application. Too much heat or too long of a residence time may degrade the protein, reduce its nutritional value, and increase oxidation in the oil.
Anti-nutritional factors: trypsin inhibitors and urease
Like humans, plants have evolved for survival and reproduction. To improve their chances of survival, plants are armed with certain defenses like toxins and antinutrients. In soybeans, the most well-known defenses are urease and trypsin inhibitors.
Urease is an enzyme that catalyzes the conversion of urea into ammonia, which can lead to ammonia toxicity and death. A trypsin inhibitor is a protein that blocks the ability of the enzyme trypsin to do its job of breaking down proteins. Reducing the biological activity of trypsin impairs the animal’s digestion of protein and nutrient utilization, often slowing or decreasing weight gain.
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Heat application during processing
A screw press, or Expeller®, is the ideal system for processing soy with nutrition in mind. A screw press does not use harmful chemicals during extraction. Heat in a screw press system, if appropriately managed, allows for optimal protein and fat conditions in the final product.
An extruder like the Anderson Dox™ works ahead of the press to mechanically shear, cook, and dry the oilseed. The Dox accomplishes this in a short residence time, typically around 30 seconds. This process reduces anti-nutritional factors and cooks the seed quickly enough to retain the quality of the proteins and amino acid profile, and limits oxidation of the oil.
The Dox is effective at reducing urease enzymes to an acceptable range. Urease enzymes require heating to approximately 300°F/149°C to fall within this range, a task the Dox can accomplish with ease. The reduction of urease enzymes does not require a long residence time at this temperature. Historically, the industry benchmark for an acceptable urease activity range is a pH level of .05-.20. However, some recent studies indicate that a higher value of .5 pH units is also sufficient.
Typically, the Dox can reduce trypsin inhibitors to about 10,000-15,000 TI units per gram. Depending on the product’s final use and the age and size of the livestock consuming the meal, this range may not be acceptable for all processors. Installing a fluid bed dryer upstream can provide further reduction of the trypsin inhibitors to even lower levels.
Like a more traditional grain dryer, the fluid bed dryer uses heat to stabilize moisture levels of the product entering a processing facility. While reducing moisture, the dryer also reduces trypsin inhibitor levels. A key difference between the two dryers is that the fluid bed dry has a shorter residence time than the grain dryer and thus is better able to preserve the seed’s protein solubility while also reducing anti-nutritional factors.
The Dox and fluid bed dryer combination can reduce trypsin inhibitor levels to the lowest amount necessary, under 5,000 TI units per gram.
Read more about system design: Critical Elements Behind Successful and Complete Processing Systems.
Value of proper heat treatment
Heat treatment can be a double-edged sword for processors. With insufficient heat, processors risk leaving behind harmful anti-nutritional factors in the product. With too much heat, processors can destroy the proteins and the overall nutritional value of the final product.
To maximize profits, processors invest in high-quality machinery designed to strengthen, not destroy, the most valuable components of the oilseed. High-quality machinery also improves profitability by reducing downtime and increasing the flexibility of a plant.
Anderson International can work with your facility management team to identify the ideal equipment based on your unique needs and process. Whether your operation requires the addition of an Expeller, Expander, or Extruder, the Anderson team is knowledgeable about all compatible upstream and downstream equipment and can engineer and supply a complete processing system.
To learn more about Anderson’s processing solutions, contact us today.