EFFECTS OF STEAM TOASTING ON THE DIGESTIBILITY AND NITROGEN-UTILIZATION OF ARGENTINE AND CHINESE SOYBEANS IN GROWING PIGS

Argentine and Chinese soybeans were steam heated at 100 degrees C for 40 min, 118 degrees C for 5 min or 136 degrees C for 1.5 min. The heat ing effects on the protein quality of the soybeans were evaluated by b oth in vitro and in vivo experiments. In the in vitro evaluation, tryp sin inhibitor activity (TIA), protein dispersibility index (PDI) and f luorodinitrobenzene (FDNB) reactive lysine were analysed. A digestion and nitrogen (N) balance trial was conducted with 32 castrated male pi gs (Dutch Landrace x Dutch Yorkshire). The results show that the highe st residual TIA for both Argentine and Chinese soybeans was observed i n the beans heated at 118 degrees C for 5 min. The soybeans heated at 100 degrees C for 40 min had the highest PDI. Lowest PDI was found in the soybeans heated at 136 degrees C for 1.5 min. The Chinese soybeans had higher TIA than the Argentine soybeans heated at the correspondin g conditions. The FDNB reactive lysine changed irregularly The net pro tein utilization (NPU) of the soybeans heated at 118 degrees C for 5 m in was significantly (p < 0.05) lower than those heated at other condi tions. The N digestibility of the soybeans heated at 118 degrees C for 5 min was also lower than others, but the difference was nor signific ant. A significant (p < 0.05) interaction between soybean origin and h eating condition was observed in the fat digestibility of soybeans. Th e fat digestibility of Chinese soybeans was improved more by the heati ng at high temperature for a short time (136 degrees C for 1.5 min). I t was concluded that Argentine and Chinese soybeans differ in response to steam heating. Heating at 118 degrees C for 5 min was not as effec tive as heating at 100 degrees C for 40 min and at 136 degrees C for 1 .5 min in view of the improvement of the nutritional value of the soyb eans.