"Cooked cereals" - what nutritionist and feedmiller should know
Dr. Heinrich Kleine Klausing
"Cooked cereals" is surely not a completely new topic for the feedmilling industry. Especially in the 80's some experts reported in the literature about this. However the questions "For which and why should grain starch be broken down?", "How can the breakdown of starch be done?" and "Which breakdown degree can be achieved?" are discussed again increasingly inside the feedmilling industry. With this article answers are given on these questions and new technical developments are presented.
The most important area where "cooked cereals" are used, is the nutrition of young animals, especially the feeding of weaned piglets. Weaning represents a drastic change for the piglets. Under nutritional physiology aspects this is characterised by a shift from a diet of high digestible protein, fat and lactose originating from the sow milk to nutrients of plant origin. During this weaning phase the activity of various digestive enzymes changes, in particular the activity of amylase, which is important for starch digestion. Figure 1 shows an overview of the results of a study by Makking dating back to 1993. By comparison with weaning time, the amylase, chymotrypsin and lipase activity dropped to just a quarter to a fifth. In the second week after weaning the concentration of lipase was still low, and the chymotrypsin and amylase activity rose to 70 and 74 per cent respectively of activity at the time of weaning, respectively. This situation must be taken into account when making up piglet diet and selecting raw materials.
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In this phase grain is, as ever, the most important source of energy. For many years now it has been successful practice to "break down" the starch in a part of the grain used in the feed so that most of it can be digested enzymatically in the small intestine with distinctly limited amylase activity. In addition to a "performance effect" in the form of improved digestibility and increased feed intake connected with the breakdown of starch, it is especially important to avoid excessive flooding of the large intestine with undigested starch. This eliminates a major viability basis for potential harmful germs such as E.coli und thus prevents diarrhoea. Such effects are more important than ever today, since on the one hand feed additives with an antibiotic effect are no longer available or are no longer accepted by society. On the other hand the application of intestine-stabilising medicaments by the responsible veterinarian is also strongly regulated. Every feeding measure that makes a contribution to keeping the gastro-intestinal tract naturally healthy should therefore be specifically reviewed and used.
Starch breakdown technologies
Various technical processes are used in practice to treat grain with a view to breaking down the starch. Thermal methods such as, for instance, infrared radiation or hot air treatment use the parameters of temperature and dwelling time. In hydrothermal methods such as toasting for example, moisture is used in addition. A combination of hydrothermal processes with the parameters of temperature, moisture content and dwelling time and mechanical treatment processes using the parameters of pressure and shear forces is found, for instance, in extruder technology. The principle of extrusion can be derived already from the name. The word "extrude" comes from the Latin and means "pushing and pressing out or through". Depending on the machine design the material is kneaded in the extruder channel by one or two auger-type shafts of different configuration - single or double shaft extruder - with a forward feed motion and is pressed through small apertures in a plate closing the end of the channel or through a gap. A model-specific high pressure - more than 100 bar is possible - is built up in the extruder channel. As soon as the product leaves the extruder it is suddenly de-tensioned and expands. As a result of the shear forces acting, the pressure, the specific process heat and the expansion effect, the material structure is modified clearly and a characteristic, visible texturing is achieved.
The process heat enters the product in one or more of the following ways:
- transfer of the mechanical energy input at the extruder shaft into a change in the viscosity of the material,
- heat transfer via steam or electric heating devices mounted outside on the extruder channel,
- direct introduction of steam into the material to be treated before or in the extruder.
With such material treatment high temperatures up to 200°C can result, whereby the action times are very short at just a few seconds. Derived from this, such extrusion processes are also described as "HTST" (High Temperature, Short Time). A further distinction lies in the material conditioning carried out prior to extrusion and the moisture content added here via the steam. With "moist extrusion" where water and steam are added via a conditioner (up to good 30 per cent moisture content in the material) it is absolutely necessary to dry the material after the extrusion process. This very energy-intensive and accordingly cost-intensive treatment step has so far prevented broad application of extrusion technology to process components for livestock nutrition.
The "opticon®" process technology developed by our company is a major further development of known extrusion technology. Figure 2 provides a look of the engineering. This achieves targeted intensive material conversion like the "moist" extrusion process described above. Thanks to the plant concept in accordance with the invention, however, no energy-costly drying of the treated material is necessary. Only a conventional cooler follows the treatment process.
Figure 2: opticon® production facility in the deuka site Höltinghausen
This newly-developed technology is applied to improve the nutritional value of various components for productive livestock and pets. One of its features is to largely break down the starch in various grain species as mentioned above. A further practical area of application is the clear reduction of the protein degradability in a mixture of soyabean and rape-seed meal in the rumen of dairy cows ("rumen-protected protein"). The opticon® process technology is also used to inactivate the urease in raw soya beans and is thus a complete high-grade substitute for the toasting process that has been customary to date.
Starch and "starch breakdown degree"
In order to understand what influences "starch breakdown" in cereal grains it is first necessary to look on the morphology and structure of starch.
Grain contains between 40 and 60 per cent starch depending on the cereal species. In purely chemical terms starch can be broken into amylase and amylopectin. The amylase, accounting for about 20 to 30 per cent of grain starch, consists of 1,4-α-glycosidically bonded glucose molecules, that in this bonding represent long helical chains. Amylopectin with about 70 to 80 per cent of the starch is a branched polysaccharide in which between 2.000 and 200.000 glucose molecules are bonded 1,4- and 1,6-α-glycosidically. The 1,6 bonding generates side chains and hence the complex branching of the molecule. The ratio of amylose to amylopectin, the chain length and the degree of branching of the glucose chains have a clear influence on the technical properties of the various grain species and their starch digestibility.
Starch is present in the floury portion of grain corn in the form of individual granula with a size between 2 and 200 µm. These starch granula can be seen clearly under the scanning electron microscope (1000-fold magnification). Figure 3a shows a photo of untreated wheat, Figure 4a shows untreated barley and Figure 5a shows untreated maize. The starch granula are held together very stably in their interior by hydrogen bridges. The branched molecule chains of the amylopectin can form semi-crystalline to crystalline areas in these granula together with the un-branched amylase molecules. This firmly organised structure is water-insoluble and in its native, non-crushed form highly resistant to enzymatic degradation.
 |  | | Figure 3: wheat, untreated | Figure 4: opticon® treated wheat |  |  | | Figure 5: barley, untreated | Figure 6: opticon® treated barley |  |  | | Figure 7: maize, untreated | Figure 8: opticon® treated maize |
By intensive mechano-hydrothermal treatment of grain (customary milling and subsequent extrusion using the opticon® technology) these structures are modified right down into the molecular range. The starch is "broken down" and improved starch digestibility is achieved in young piglets with distinctly limited amylase activity in the small intestine. The main effects occur as a result of clear enlargement of the surface and far-reaching disintegration of the semi-crystalline and crystalline areas and of the amylopectin and the amylase. These structural changes are clearly visible under the scanning electron microscope, as shown in Figures 3b, 4b and 5b. The typical starch granula are largely destroyed by the treatment and chiefly melted together to form flat areas like melted plastic.
It is common knowledge that the degree of starch modification is influenced substantially by the process technology used and the physical parameters effective here. This modification can also be determined analytically as "starch breakdown degree" with the "Amyloglucosidase Method" (AMG-Method) (Agricultural Testing and Research Institute Nord-West, LUFA Nord-West, 2003). In this method the material to be examined is mixed with the enzyme amyloglucosidase after various preparatory steps have been taken. This enzyme splits off glucose on starch molecules solely at the end of the chain. The glucose split off is measured after an incubation period of 15 minutes. The content of hydrolysed starch is calculated from this and set in relation to the crude starch content.
Why is the enzyme amyloglucosidase used in this method, and not the α-amylase present in the piglet's digestive tract too? By comparison with amyloglucosidase, the α-amylase attacks starch molecule chain and molecule fragments. Jansen (1989) states in this connection that such fragments also occur as a result of the technical treatment of the starch and therefore a detection process using amylase or a mixture of α-amylase and amyloglucosidase would not be suitable. Treatment and enzyme effects would be superimposed on each other and the useful information provided by the result would therefore be very limited. That is why the AMG method has been considered for many years as the suitable method for determining the degree of starch breakdown.
The duration of incubation with the enzyme amyloglucosidase and the temperature conditions under which incubation occurs are crucial for the values determined and for comparability of the degrees of breakdown in different grain treatment methods. Using the method described here the starch breakdown degree is determined in standard fashion with an incubation period of 15 minutes at a temperature of 50°C. These parameters are always stated with the results. Furthermore, to interpret the results it is important to know that according to the information supplied by the Agricultural Testing and Research Institute (LUFA Nord-West (2003)) the values determined can only be compared directly with one another within the same grain species.
Influence of the treatment
The opticon® technology is used as a standard to produce wheat broken down hydrothermally. The refined product is used within the company to produce specialised piglet rearing feed varieties such as pre-starters, weaning starters and special rearing feed. This broken down wheat is used under the brand name optiwheat®, presented in Figure 6 by compound feed producers in Germany and other neighbouring countries in Europe too. Within the framework of quality assurance production samples are examined for their starch breakdown degree* using the AMG method in accordance with a fixed code. The tests conducted to date in the year 2003 resulted on average in a starch breakdown degree* of 71.9 per cent (s = ±3,5 percentage points) for the optiwheat® product.
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In addition to wheat, the process technology can also be used to break down barley and maize mechano-hydrothermally. Appropiate studies have also resulted in a starch breakdown degree* of over 70 per cent on average for opticon®-treated barley too. However, it is more difficult to modify the starch in maize than in wheat and barley. This is attributable to a change in the order condition of starch during drying of maize observed by Münzing (2003a). Due to the much higher moisture content on harvesting by comparison with wheat and barley, maize must always be dried intensively. According to Münzing (2003b) individual molecule chains associate during such intensive thermal treatment, either by amorphous areas of the starch gradually transferring to a thermodynamically more stable condition, or by the starch crystallite being perfected by further aggregation of the compacted sequences. Grain specialists describe this change as a "tempering or annealing effect". This makes the starch less prone to thermal, hydrothermal, mechanical and pressure-mechanical, as well as enzymatic and microbial attacks. This is also the reason why native maize starch is more poorly digestible for young monogastrics than, for instance, wheat starch or shows higher rumen stability among ruminants. Results of the average starch breakdown degree* of opticon®-treated maize (opticorn®, Figure 7) of 65 per cent are further evidence of this connection.
 |  | | Figure 9: optiwheat® | Figure 10: opticorn® |
Summary
Today piglet nutrition makes higher demands on feeding than ever before. "Performance and health" can be supported substantially by diets adapted to the digestive capacity of the piglets in the individual rearing phase. "Broken-down grain" plays a central role here and is today no longer simply a product for "pre-starters", but is also increasingly being used successfully in rearing feed concepts.
In addition to the known mechano-hydrothermal techniques for "breaking down starch" in grain, the opticon® technology presented here provides a new process that represents a major further development of known extrusion technology. A high degree of substance modification is achieved in the treated products without the finished product having to be subsequently dried. The starch breakdown degree* achieved in wheat and barley of on average over 70 per cent and the average of 65 per cent for maize document the effectiveness of the process.
* average starch breakdown degree (AMG-Method): Incubation 15 minutes at 50°C
Literature
JANSEN,H.-D. (1989): Veredlung von Getreide und Leguminosen durch Wärme, Druck und Scherkräfte
Mühle + Mischfutter, 126, 360-364
LUFA Nord-West (2003): personal report Dr. Egert 28 August 2003
MAKKINK, C.A. (1993): Of pigs, dietary proteins, and pancreatic proteases
PhD-thesis
MÜNZING, K. (2003a): personal report Dr. Münzing 29 August 2003
MÜNZING, K. (2003b): Aktuelle Probleme bei der Qualitätssicherung der Weizenernte 2003
Mühle + Mischfutter, 140, 553-556
Oktober 2003
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