For several years, there has been interest in using whole unextracted, full-fat soybeans in poultry and livestock rations. Because soybeans contain both a high quality protein (38-42%) and a rich source of oil (18-22%), they have the potential to supply major amounts of protein and energy to poultry and swine rations. Numerous studies have been conducted which demonstrates that properly processed whole soybeans may be used efficiently in livestock rations. The subject has been reviewed by various people, including Waldroup (1982), Monari et al. (1996) and Lazaro et al. (2002). These investigations indicate that soybeans are an excellent source of protein and energy for poultry. However the raw grain contains certain antinutritional factors that inhibit productivity, and as a result, prior heating is required.
If fullfat soybeans are not previously subjected to some form of heat treatment, their nutritive value is relatively low. Furthermore, raw fullfat soybeans may adversely influence animal health if fed. This is a consequence of the presence of biologically active compounds with an antinutritive action. Although the most important of these are protease inhibitors and haemagglutinins/lectins, saponins together with allergenic, goitrogenic and rachitogenic factors may be present.
Heat treatment is the most common method used to reduce any antinutritional factors present in raw soybeans. The mechanism by which the heat inactivates these antinutritional factors is known as denaturing. Nevertheless, if a protein source overheats, its amino acid availability, in particular that of lysine, drops.
Several methods are available and are all based upon a combination of temperature and time with sometimes additional moisture, added occasionally as steam. The methods include:
Extrusion - soybeans are extruded between 132 ºC and 149 ºC. Temperatures may range from 80 to 200 ºC. The product is pressed under high pressure through a narrow opening (die). Dry or wet extrusion types are available. One or two screws are available. Residence times are from 30 to 150 seconds.
Expanders - temperatures range from 70 to 170 ºC for 5 to 15 seconds. Only one screw is present, mainly for transport. Addition of water, steam and pressure is used. The essential difference between extrusion and expansion is that the latter is less energy- intensive and that at the exit of the installation, the matrix is replaced by a conical discharge valve.
Jet-sploding - the beans are sent through a stream of air pre-heated to 140 to 315ºC rather than being directly exposed to the flame. The molecules vibrate in the heat, the intracellular water cooks and the grain heats up from the inside out, reaching inner temperatures of 90 to 95 ºC. The seeds swell up and pop. In general, after heating, the beans are placed into a cylinder mill in order to finalize the process and facilitate the release of the intercellular fat.
Flaking - hydro-thermal treatment is based on injection of low pressure steam into a conditioner. The heated Full Fat Soybean are flaked by forcing them through two rollers.
Cooking - this is a relatively simple process to use. The raw beans are immersed in water and cooked for between 30 and 120 minutes. They are then dried mechanically, or alternatively spread out on the ground. These beans are then eaten whole, ground or crushed.
Roasting - can be either batch or continuous. Gas flame or electricity can be the energy source using temperatures ranging from 100 to 210 ºC. Several models exist, including conventional “dry” systems and moist heat systems. The heat used for the latter can be generated by an oven, a coal burner or directly by a flame. The temperature reached varies between 110 and 170ºC depending on the equipment used. The simplest of these processes involves the direct and intensive application of dry heat (roasting) for around 20 seconds. This process reduces the initial moisture of the bean by 30%, but without breaking down the cellular structures, or releasing their oil. For this reason, the beans must be further milled or laminated before being used as food.
Micronizin - is a dry heat process that uses radiating heat as an energy source. This method is based on the process of heating ceramic containers using gas or electronic burners. Once these ceramic plates reach a certain temperature, they emit infrared rays which are a type of radiation but at a higher frequency than microwaves. This type of radiation is extremely efficient for heating the inside of absorbent materials and penetrates the beans creating an intense bout of molecular movement, which in turn leads to a rapid increase of the inner temperature and the water vapor pressure.
Microwave - temperatures up to 150 ºC are used, but for short time intervals, of around 60 seconds. High investment and operational costs are unfortunately involved. Seeds are heated by IR-radiation. Gas fired IR heaters are used as the energy source.
Lázaro, R.; Mateos, G. G.; Latorre, M. Á.; Piquer, J. (2002)
Whole soybeans in diets for poultry
Mateos, G. G.; Latorre, M. Á.; Lázaro, R. (2002) Processing soybeans (http://www.asa-europe.org/pdf/processsb.pdf**).
Monari, S. (1994) Fullfat soya handbook. 2ª ed. American Soybean Association.
Brussels. 44 pp.
Waldroup, P.W. (1982). Whole soybeans for poultry feeds. World's Poult. Sci. J., 37:28-35.