The use of products from soybean, rapeseed, etc. in the feed and food industry has increased steadily. For instance, the crude protein of soybean meal (SBM) ranges from 41 to 50% (dry matter basis) depending on the amount of hulls that is removed, and the processing method used. While the amino acid profile pattern is probably the main determinant of protein nutritional quality, the digestibility of a protein and bio-availability of its constituent amino acids are the next important factors. The differences in protein digestibility are brought about by the susceptibility of a protein to enzymatic hydrolysis in the digestive system and this is directly related to the primary, secondary and tertiary structure of the protein. During solvent processing, lipids are removed and the meal is heated to eliminate the solvent (usually hexane) and to deactivate antinutritional factors such as trypsin inhibitors and lectin. Inadequate heating fails to completely destroy the antinutritional factors but overheating results in undesirable changes to the chemical structure of many essential amino acids. So, both insufficient- and over-heating result in poor quality of meal. Therefore, meal processors and their customers in the animal feed industry need reliable, rapid and cost-efficient methods to control the quality of their soybean meal.
Of tests commonly used, the quality of meals is evaluated with indirect tests such as Protein Dispersibility Index (PDI), Nitrogen Solubility Index (NSI) and KOH protein solubility (PS). The KOH protein solubility (PS) consists of determining the percentage of protein that is solubilized in a potassium hydroxide solution. The PDI is one of the simplest, most consistent, and most sensible method. This test measures the solubility of proteins in water and is probably the best adapted to all soy products. The PDI method measures the amount of protein dispersed in water after blending a sample with water in a high-speed blender. The water solubility of protein can also be measured with a technique called NSI, differing in the speed and vigor at which the water containing the soybean product is stirred.
All of these tests are available at IMPROVE, so don’t hesitate to contact us for further information!