Depending on precondionner’s applications the single shaft one can sometimes be enough. However when precooked functions are necessary then it is better to work with birotors. We can sometimes even get 3minutes retention timing with hydration rate around 25 to 27%.

Blades are included in the mixing configuration allowing good mix quality. Each blade has its own function; the smallest one is going to mix while the bigger one is keeping away the product. Injections are also planned such as slurrys,oils to guarantee the perfect mixing homogeneity before extrusion.

A sustainable alternative to traditional animal flour (meat and fish) would be the production and use of insect proteins.

Why insects ?

Insects have always been part of the diet of animals and humans. Indeed nearly 2.5 billion people consume it regularly, and are an integral part of the diet of most wildlife:

• 40% in trout
• Up to 50% in poultry, pheasants or growing partridges
• 5% in wild boars
• 3% in cats and dogs

Insects are rich in high quality proteins, fatty acids and essential amino acids, and are therefore the ideal candidates for the substitution of animal proteins used especially in the diet of fish and domestic animals.

Development challenge

The need for insect flours in animal nutrition can be estimated at 100,000 tons per year in the long term. To be able to answer this request it is important to find efficient breeding methods on a large scale. In France, their number is constantly increasing, but they come up against certain technical and regulatory obstacles.

Actually the industrial breeding is energy-consuming, the storage of the larvae in mass causes a heating, the insects being ectotherms (does not regulate their temperature) it is necessary to control the temperature in breeding places. To dissipate this heat, solutions are needed to stir the mixture and circulate air between the layers and these systems consume large amounts of electricity. Species choice; reproduction mastery, raw material supply management and the management of the sizing and processing of finished products will determine production viability.

In addition, the sector faces regulatory blockages:

• Prohibition of the use of animal protein in farmed animal feed
• Limitation of permitted substrates as insect feeds: no manure or slurry, no restorative waste or expired food.

Nevertheless since July 1st it is allowed to use insect meal in the diet of farmed fish. So today insect flours are allowed only for fish feed and pet food.

Tests performed

As shown in the table below, experiments with 3 mm extruded feed containing 30% Hermetia illucens flour underscore digestibility of crude protein and lipids above vegetable meal.

There are many benefits to insect flours, such as being high in high-quality protein, essential fatty acids and amino acids, highly digestible, and breeding that conserves natural resources. In order for these flours to become an essential component of animal feed and no longer a niche market, the price factor is crucial. They must be able to compete with fishmeal in fish feed and meat flours in the Pet Food, the only species where they are allowed today.

Pre-cooked flours are nowadays very popular among consumers compared to native flours, because of their convenience of use, their improved nutritional and organoleptic qualities and their extended shelf life. Extrusion cooking stands out from other processes by different competitive advantages: versatility; ease of integration into complete production lines; wide adjustment and automation possibilities; high energy efficiency; high production capacity, and specific nutritional and physicochemical characteristics conferred on the flours thus treated.

Applications of extruded flours for human consumption

Extruded flours are mainly used as complementary food, in infant nutrition or in humanitarian intervention programs. In these two cases, they are obtained by formulation of mixtures of flours and by systematic mineral-vitamin fortification. The objective is to balance the qualitative and quantitative contributions in macro- and micro-constituents. In order to get as close as possible to nutritional recommendations regarding:

• Energy value provided by fat;
• Nutritional quality of the incorporated proteins: the amino acid composition can be adjusted by a good complementation cereals / legumes;
• Essential micronutrients (minerals, vitamins, acides3 fatty acids);
• Limitation of factors that may cause intolerance or discomfort reactions, such as gluten and fiber for young children.

Infant flours produced by extrusion cooking

For infant flours, the WHO recommends that they be used only after 6 months. At this age, infant flours can then be introduced in addition and then gradually replacing breastfeeding, after rehydration with water or milk. The rehydration rate depends on the age of the child in order to adapt to his physiological needs: slight thickening of the infant milk supplied to the bottle (2nd age) then boiled more and more consistent, administered with the spoon (children over 12 months). At this level, the extrusion cooking is of specific interest because of the highly fluidifying behavior that the dextrinization of the starch confers on the reconstituted slurries. This allows, for the same viscosity threshold, to very substantially increase the rate of incorporation of dry materials into the reconstituted slurries and therefore increase their nutritional and energy density.

Another factor to take into account is the more or less cooked and instant character of these flours. These flours are classified into three groups:

• Cooking flours, which have yet to be cooked for at least 15 minutes;
• Pre-cooked flour, which must be boiled for 5 to 10 minutes;
• Instant flours, not requiring additional cooking.

It should be noted that the digestibility of the starch is correlated with its rate of gelatinization, a process known to occur by cooking in excess of water. Regarding the extrusion cooking, this explains the advantage of favoring a treatment wet rather than dry. Moreover, it makes it possible to pre-cook the starchy base first and then, after treatment, to add the heat-sensitive vitamins as well as any protein enrichment (milk proteins) and sugar. Such a protocol prevents the development of Maillard reactions that cause, under the effect of cooking, the immobilization of lysine by reaction with sugar. Instant flours also limit energy costs and preparation time; it therefore improves practicality while optimizing the nutritional and hygienic quality (sterilizing cooking), as well as the conservation of flours.

Nutritional supplements used in food aid

In humanitarian contexts, pre-cooked meals can be incorporated into basic food rations distributed to the intended beneficiaries. For groups at higher risk (young children, pregnant or lactating women, patients with various pathologies, including AIDS), they can be added as additional rations to strengthen nutritional intake, prevention of malnutrition or treatment of moderate malnutrition. Between 200,000 and 300,000 tons of such flours are distributed annually by the World Food Program, many of which are produced locally and almost exclusively by extrusion cooking. As this process makes it possible to incorporate a wide range of raw materials, each country can adapt its recipes to locally available resources.

Production line and process control

The manufacture of extruded flours goes through the steps described in the following diagram:

With regard to equipment and their behavior, the following points should be particularly monitored:

• Hygienic quality control (HACCP approach): limiting the risks of water recovery after extrusion
• Degree of cooking control
• Control of the flour formulation: efficient dosing and mixing systems, particularly for the premix of vitamin-mineral to be incorporated and its homogeneous distribution in flour
• Final granulometry control, to limit the presence of hard spots during the reconstitution of the pores; sieving system with recycling of waste.

Crédit^© Dominique Bounie

 Maillard’s reactions commonly used in cooking for their organoleptic characteristics are very interesting for feeding ruminants. Indeed proteins and sugars react together to form indigestible complexes in the rumen: Bypass protein. These Maillard’s compound are dissolved thanks to the acidic pH of the abomasum, the amino acids they contain become again fully available to be absorbed in the intestine.

Digestive system of cattle

Maillard’s reactions occur in the presence of amino acids and sugars at temperatures between 0 and 150°C, a pH between 6 and 10 and a humidity of about 15%. As shown in the graph below, the temperature has a strong influence on the reaction rate. During extrusion cooking, it is therefore possible to adjust the parameters: temperature and mixing passage time in order to cause or not Maillard reactions. Indeed it is interesting to facilitate these reactions for the production of ruminant feed but it will be important to limit them to the minimum for the production of poultry food for example. Indeed the Maillard’s compounds reduce the protein availability for monogastric species. A good mastery of the extrusion cooking makes it possible to choose characteristics of the product according to the anatomy of the target species.

By their composition, Soybeans are very interesting for animal nutrition. Indeed their contain between 18 and 20% of fat, source of energy; between 35 and 38% of proteins, but also many anti-nutritional factors preventing good beans assimilation by various digestives systems. In particular proteases (trypsin inhibitors) preventing beans digestion, hematoagglutinins (lecthins) that prevent nutrients absorption but also allergenic factors that can affect especially milk calves. In order to benefit most of soy beans nutritional components, extrusion is the best treatment. In fact, it improves proteins digestibility by 11%, lysine by 14%, methionine by 11% and cystine by 5% compared to raw beans, but also by reducing raw amino acid content and therefore undigested protein.

Technical study

In order to obtain a product with a lower energy intake facilitating rations balance, it is attractive to operate a partial extruded beans deoiling. By this way, fat content decreases from 20% to about 5.4% in meals while collecting a product with high added value: soybean oil. In animal feed, the element feed industry are looking for is protein level. Lowering fat content permitted to increase meals protein rate while collecting a co-product.

The conventional method includes two phases, as shown in the figure below. In order to further reduce meals fat proportion, a solution under study is adding to extruders’ barrel a special chamber to collect oil. Therefore fat content at extruders exit is 1 to 2% lower, facilitating presses work which can then produce meals with a lower fat rate.

1) Dry extrusion

Dry extrusion allows beans to be cooked at a high temperature, around 150°C for a very short time of a few tens of seconds. Heat is provided by mechanical energy created by shear and friction forces in extruders. In extruders’ barrel, water naturally present in beans remains liquid because of high pressure (several tens of bars), but, on dies’ exit, beans regain atmospheric pressure which causes:

• Immediate water evaporation passing extruded beans at a humidity rate of 6%
• Destruction of cells’ walls that contain oil, facilitating presses work
• A brutal drop in temperature stopping all reactions of browning

2) Mechanical pressing

Extrusion allows a better bean deoiling than flattening-cooking-pressure (FCP) method, indeed at extruder’s exit, cells containing fat are destroyed and oil is free. Also extruders work as preparers; it allows presses to have better performances, to work at higher rates and to have lower rates of wear. Experiments show that meals contain an average of 1.3% less oil than FCP meals. In addition, as shown in the table below, extrusion and then pressing treatment produces greater output of both oil and meal while having less water losses.

EP = extrusion pressure      FCP = Flattening Cooking Pressure

As outlined in the table below, extrusion then pressure produces meals containing about 45% protein and a fourfold division of antitrypsic factors. In addition, treated products are very stable, accepting a conservation of several months through lipases and lipoxidase destruction, and low free water content. This avoids preservatives addition; since products are not affected by rancidity, oxidation or mold.

Composition of soy products

Economic study

From an economic point of view, it is important to know the cost  of this treatment per ton of soybean. Assuming a factory produce 20,000 tons per year corresponding to an average of 3 tons per hour, budgets are summarized in the table below:

Data: Interest 2%, Electricity: 0.05775 € / kWh

Excluding raw material, an extruded and then squeezed soybeans ton cost is less than 35 €.

In poultry feed, extrusion is the best soybean treatment. Actually it allows:

• a better energy rate, increasing by 32% compared to raw seeds, 13% compared to toasted seeds but also more than 6% compared to infrared treatment.
• A total destruction of the cell’s walls that contain the oil, making it available to attack digestive enzyme.
• Optimum preservation of the biological protein value by dry extrusion, thanks to a progressive temperature rise while descent is instantaneous allowing proteins to reach 150°C for less than 3 seconds.
• A 90% antitrypsic factors destruction, responsible for raw seeds bad digestibility.
• Does not affect triglycerides structure (fat). Indeed the maximum temperature of 150°C is lower than fat decomposition temperature (more than 180 ° C), which makes them available for animals. In particular, it contains an interesting content of Omega 6 (linoleic acid): about 10% of the raw product, as well as Omega 3 (linolenic acid), which is particularly profitable for laying hen.
• Good preservation thanks to their low moisture content and lipolytic enzymes destroyed by extrusion.

As far as dairy cows are concerned, it is difficult to calculate the energy value of standard extruded soybeans. The French system is UFL (dairy feed unit), commonly calculated using an equation based on raw material composition. But it does not take into account components digestibility or interactions between them. We must find another method of evaluation. INRA has developed truly digestible proteins in the intestine system (DPI) consisting of the sum of:

• Food proteins that have passed through the rumen without modification: by-pass proteins (DPIA)
• Proteins elaborated in the rumen by microorganisms (DPIM)

With this method, it is possible to compare extruded and raw soybeans’ characteristics according to their residence time in the rumen. The longer the residence time of rumen’s soybean increases, the lower is the DPI content, but this is especially true for raw beans -43% against -16% for extruded beans. In addition, extruded beans contain between 45 and 110% more DPI than raw beans. With regard to by-pass proteins, extrusion cooking makes it possible to increase their number between 100 and 300%. These calculations highlight profitability of soybeans extrusion into dairy cows diet.

Livestock farming techniques have changed over time and now require greater precision. Today, intensive farming must meet new demands from consumers, especially where the nutritional value of the products is concerned.
New types of crop can be used to enhance digestibility and eliminate their toxic or anti-nutritional factors before they are incorporated into the formula.

Virtually instantaneous heat treatment of HT-ST (High Temperature – Short Time) type specifically used in extrusion allows products to be stored for several months with no deterioration.

Although the initial application of extrusion to animal feedstuffs targeted pet food and aquaculture, extruders have gradually begun to appear on the market with modular, robust and flexible designs that make them more economically advantageous.

Such extruders have in fact been used in the heat treatment of oilseeds as has been confirmed by Dr Legoy in the past : “ The technology used can destroy germs contaminating the oilseeds and remove certain anti-nutritional (antitrypsic factors in whole soya beans, rapeseed glucosinolates) and enzymatic factors (lipases and lipoxidases involved in the oxidation of oils for example). Added to this is the destruction of cell walls, which enhances the digestibility of the energy contained in the product (oils, gelatinised starches) and heat treatment of the proteins leading to protein insolubilisation, especially in feed for ruminants. ”

Extrusion applications for animal feed are diverse. The internal configuration of an extruder is easily adapted to suit a wide range of types of operation.
Some examples:

• The processing of whole soya beans for incorporation of significant percentages in pig and poultry feed,
• The manufacture of highly effective feedstuffs and supplements for high-production ruminants,
• The production of special feedstuffs (pet foods, shrimp feed, floating or controlled-descent sinking feed),
• The stabilisation of by-products (low-grade rice flour, dressing and filleting waste, etc.).