[Effect of various extrusion conditions on the protein quality of soybean and whole rye meal].

Using a Creusot-Loire twin-screw extruder (Type BC 45), ground soy bean and whole rye meal were extruded under various processing conditions (12% and 18% water content in the raw material, 129 degrees C and 165 degrees C product temperature in the case of soy bean, 12% and 18% water content, 165 degrees C product temperature in the case of rye, screw speed of 150 R/min, for all samples). The nutritional protein quality (apparent protein digestibility PV, net protein utilization NPU, and biological value BW) of the extrudates was determined by the nitrogen balance technique in growing rats. Compared to the untreated raw material no decrease in PV or NPU was noted for extrudates made from soy bean or rye. Extrusion of ground soy bean at 165 degrees C and 18% water content caused a significant decrease of BW from 68% to 64%. The lower water content (12%) induced a slight improvement of PV in soy extrudates and of NPU and BW in rye extrudates. The results indicate that the extrusion at low water content and moderate temperature can safely be used to process ground soy bean and whole rye meal without and damage to the nutritional protein quality.