Soya beans are an excellent source of protein but they also contain anti-nutritive components, which need to be deactivated by heat prior to feeding to swine or poultry. However, high temperatures can also damage key nutrients, reducing their digestibility.
Trypsin inhibitor activity (TIA), protein dispersibility index (PDI) and urease activity are useful indicators in soya products to assess the quality of soya bean processing and help to predict availability and digestibility of nutri-ents. Most feed laboratories can measure these parameters. In addition, specialised near infra-red spectrosco-py (NIRS) can now measure the availability of amino acids.
Regular monitoring of key soya bean processing indicators is essential for achieving a consistently high product quality. Results can be also used by animal keepers for planning feed rations.
Processing intensity is key to quality
Common procedures for the heat treatment of soya beans are toasting, steaming and extrusion. The purpose of these procedures is to deactivate anti-nutritive components such as trypsin inhibitors. However, applying high temperatures inevitably leads to nutrient damage so the goal is to balance processing intensity. For toasted soya beans, the intensity is a function of processing time and temperature.
Crude protein content is a standard feed parameter, but it does not provide information on the digestibility. Processing indicators are measurable components of soya feed products which make the quality of soya bean processing (heat treatment) quantifiable. Table 1 summarises processing indicators which best predict the digestibility of the feed. Nutrient availability can be high if the values for trypsin-inhibitor activity (TIA) and protein dispersibility index (PDI) are within the target range (see numbers in Table 1). On the other hand, a poor feed conversion ratio becomes more likely if, for example, the TIA value in soya cake is higher than 4 mg/g (see Figure 1).