Abstract: 【Objective】Soybean is an important food material as well as feed material for its abundant nutriments, but some antinutritional factors (ANFs) in soybean limit its application in the food and feed industries. As a widely used processing technique, the extrusion process can reduce the side-effect of ANFs in soybean to human and animals causing the content of ANFs to decrease while the content of nutrient composition remains about the same. This research is aimed at investigating and analyzing the difference of main antinutritional factors in soybean and extruded soybean and discussing the effect of the extrusion process to these ANFs in soybean, so as to provide a reference for expanded enterprises to choose high quality raw materials and optimize the processing technique in the actual production, and provide some guidance to the design of animal feed formula. 【Method】In this research, 20 batches of soybean and 19 batches of extruded soybean from different areas of the manufacturer were collected, and the content or activity of the main anti-nutritional factors, including trypsin inhibitor, antigenic protein (glycinin and β-conglycinin), oligosaccharide (raffinose and stachyose) and urease, were detected. And these results were compared with 2 batches of soybean and 8 batches of extruded soybean that were produced in one manufacturer. The concentrations of trypsin inhibitor and antigenic protein were analyzed using ELISA. The concentrations of oligosaccharide were determined by HPLC with a differential detector. At the same time the extraction methods of oligosaccharides were optimized. Single factor optimize experiments were the way of extraction, the dosage of activated carbon, volume percentage of ethanol, and solid-liquid ratio. The solution was detected by HPLC after through filter membrane. Through comprehensive analysis of the data, the effect of extrusion technology on the content or activity of main antinutritional factors in soybean was studied. 【Result】 The extraction method is as follows: adding 70% ethanol solution to the samples (solid-liquid ratio: 1﹕25), and then centrifuging and concentrating the extracting solution after using microwave assisted extraction, diluting the concentrated solution with water to 25 mL, centrifuging the solution (2 mL) after blending. In comparison the content of the main antinutritional factors in soybean (22 batches) with the content in extruded soybean (27 batches), the content of trypsin inhibitor and antigenic protein and urease activity in soybean is significantly lower than those in extruded soybean while the content of oligosaccharides has no significant difference between them. The urease activity of most of extruded soybeans is near zero and lower by 99% than the activity of soybeans. The content of trypsin inhibitor, glycinin and β-conglycinin decreased respectively in 66%, 67% and 90%, while the content of raffinose and stachyose remained largely unchanged. From this research the content or activity of trypsin inhibitor, glycinin, β-conglycinin, raffinose, stachyose and urease in the soybean is respectively 32.5-89.6 mg·g^-1, 91.0-143.1 mg·g^-1, 161.1-268.7 mg·g^-1, 3.3-8.78 mg·g^-1, 21.4-34.16 mg·g^-1 and 3.6-9.42 U·g^-1, in the extruded soybean is respectively 10.7-31.1 mg·g^-1, 17.7-64.5 mg·g^-1, 9.3-57.5 mg·g^-1, 4.25-10.21 mg·g^-1, 17.68-34.15 mg·g^-1 and 0.00-0.02 U·g^-1. 【Conclusion】 The extrusion process can significantly reduce the content of the main antinutritional factors in soybean and side effects caused by these factors and can improve the utilization rate of nutrition. This study presents the reference range of the main ANFs in content or activity in soybean and extruded soybean.

Key words: soybean, extruded soybean, extrusion, antinutritional factors, nutrient composition