Hydrothermal treatment of monocomponents

Apart from the flat die pellet mill, the expander is one of the best-known machines from KAHL. In feed production, it provides a number of advantages, from hygienisation to improved pellet quality. The advantages of using an expander with the associated hydrothermal treatment become particularly evident in the treatment of monocomponents such as soybeans.

Markus Lukaszczuk
Area Sales Manager
Amandus Kahl

Soybeans are the most important oilseed in agriculture worldwide. About 6% of the global agricultural land is used to grow soybeans. Usually, the oil content of the bean of about twenty percent is expelled or extracted and used in human nutrition. The remaining soybean expeller and soybean extraction meal have a protein content of 35% (soybean expeller) or 48% (soybean extraction meal). Thus, around 80% of the original soybean is used in the feed industry in the form of expeller and extraction meal. These protein concentrates are used in the feed industry for a reason. Press cake and extraction meal have a very good sequence of amino acids, which ensures an excellent animal performance. In addition, the protein concentration of the feed rations can be increased very efficiently due to the high protein content.

Expanded Soybeans, ©Petrolle Photography

Using soybeans in the production of animal feed does not mean, however, that soybeans have to be imported from South America or the USA. The use of European soybeans, which are also not genetically modified, is an obvious choice if we want to take into account the ecological aspects and leave a significantly smaller carbon footprint. As a result, the demand for this GMO-free soybean is steadily increasing.

The nutrient composition of soybeans may vary considerably. Depending on the climate zone of the growing region and the variety used, the protein content, protein solubility, energy content and the content of anti-nutritive substances vary. These factors require a nutrient analysis of each batch of soybeans.

In general, soybeans must undergo hydrothermal treatment before they are used in poultry and pig feed so as to achieve the inactivation of trypsin inhibitors which have an antinutritional effect. Trypsin inhibitors are secondary plant substances and count among protease inhibitors. These protease inhibitors interact with the enzyme group of trypsins and inhibit the proteolytic activity of digestive enzymes in general. This inhibitory effect reduces the digestibility of nutrients.

In broiler fattening, maximum proportions of 15% soybeans can be mixed into the ration in the first to fourth week of life. In the final fattening period, proportions of up to 20% are possible. Higher additions to the feed will result in an oily consistency of the abdominal or visceral fat.

A similar alteration of the fat can also be observed in fattening pigs. The alteration of the fat is due to the high content of polyunsaturated fatty acids in the soybean. Therefore, the admixture should not exceed a maximum of 10% in the final fattening period.

In cattle feeding, it is especially the enzyme urease that may cause problems. The urease content in the soybean accelerates the breakdown of urea to ammonia and speeds up the cleavage of proteins in the rumen. This leads to an excessive influx of ammonia in the rumen, which reduces the animal performance. Therefore, only small quantities of soybeans that have not been hydrothermally treated can be used in cattle feeding.

Cross-section of the crown expander, ©AMANDUS KAHL

This shows how important hydrothermal treatment is for the use of soybeans in animal feed. It is important that this treatment is gentle in order to avoid a too significant alteration of the proteins contained and to keep them available for digestion.

The protein solubility in H2O and KOH acts as an indicator for gentle treatment of the soybeans. This value ensures that proteins and amino acids remain largely intact during hydrothermal treatment. Depending on the variety, the protein solubility of the raw soybean can also vary greatly. A treatment must therefore be adapted to the raw material.

The table above shows how much domestic soybean varieties can vary in terms of their composition. In particular, protein solubility and trypsin inhibitor activity are important indicators for a successful hydrothermal treatment. To ensure successful treatment, a constant analysis of the raw material is necessary. Subsequently, the parameters of the hydrothermal process must be adapted in order to optimise the treatment. The crown expander enables an easy adjustment to the raw material. As an alternative, the retention time in the conditioner can be adjusted in no time.

Like trypsin inhibitors, urease is inactivated during thermal treatment. The analytical determination of trypsin inhibitor activity (TIA) is very complex. Therefore, in practice, the urease activity which is easier to determine is often used as a reference. This is possible as these two values correlate with each other.

Compound feed plant in Poland with hydrothermal reactor and expander, ©AMANDUS KAHL

In the following, the design and the process of a hydrothermal plant from AMANDUS KAHL are explained: Prior to hydrothermal treatment, the soybeans are crushed on a crushing roller mill. After crushing, the product is free-flowing and can be heated up quickly due to its high specific surface area.

In a mixing conditioner, the product is heated by means of steam before it gets into the hydrothermal reactor. This reactor is a cylindrical bin with several levels in which agitator arms keep the product in motion. Temperature and humidity are regulated by means of a heat exchange system in the floors and the possibility of direct steam injection. The increased moisture (approx. 20%) and temperature (100°C) “soften” the bean and antinutritional factors are reduced to a certain degree already at this stage. In this step, the crushed product dwells at approx. 100°C for a defined period of time before it is further treated in the expander.

Processing the soybean in a KAHL expander provides a thermomechanical HTST treatment (High Temperature Short Time). This process make use of the fact that at high pressures (30 to 70 bar) and high temperatures (120 to 140°C), the water contained in the product is still in a liquid state. Once the product leaves the expander at the outlet and the pressure drops to 1 bar, the water evaporates abruptly and breaks the cells of the bean. This process further reduces the anti-nutritive substances significantly. Subsequently, the beans are gently dried to storage moisture with the KAHL belt drier.

It should be pointed out here that a combination of long-term and short-term treatment also allows the increase of bypass protein (UDP) in extraction meal and the modification of starch in cereals. Using the innovative crown outlet ensures the highest flexibility for different aims of treatment. The hydraulically adjustable cone allows the setting of different specific energy inputs and provides an optimal product treatment of different products.

The hydrothermal process by AMANDUS KAHL safely inactivates anti-nutritive factors such as trypsin inhibitors and urease. At the same time, high protein solubility is maintained, which ensures optimal digestibility of the proteins. The following table shows the results of a typical treatment of full-fat soybeans. The TIA in the raw material can be reduced to values ranging from 6.5 to 4 mg/g using the standard treatment (see left column in the table) by AMANDUS KAHL. After this treatment, it can be fed to cattle and adult monogastrics without reservation. Feeding to young animals requires a more intensive treatment (see right column in the table) with a longer preconditioning period.

With this more intensive treatment, the TIA can be reduced to values lower than 4 mg/g which indicate an optimal treatment. The activity of urease can be almost completely inhibited. Values lower than 0.4 mg/g*min are considered safe for animal feeding. At the same time, the high protein solubility of around 20% is maintained thanks to the AMANDUS KAHL process. Thus, an optimum digestion is ensured. (Asam et al. 2014)

Soybeans are of great importance for animal feeding. To be easily digestible, however, they must be treated hydrothermally before being added to the feed. In addition to the process described, there are other treatment methods, such as (dry) extrusion at high temperatures (> 150°C). Toasting with an open flame or infrared radiation (> 250°C) are also frequently used. These processes typically involve not only higher temperatures than the hydrothermal process, but also lower moisture levels. These processes also sufficiently destroy the anti-nutritive factors, but at the same time they cause a stronger denaturation of the soybean components, thus reducing the nutritive value of the soybeans.

During the hydrothermal treatment presented here, the high moisture contents protect the protein against a too high degree of denaturation while reliably reducing the anti-nutritive substances. This process achieves these different effects in equal measure.