THERMAL-PROCESSING OF WHOLE SOYA BEANS - STUDIES ON THE INACTIVATION OF ANTINUTRITIONAL FACTORS AND EFFECTS ON ILEAL DIGESTIBILITY IN PIGLETS

Two experiments were conducted to investigate the effects of steam pro cessing on the nutritional improvement of full-fat soya beans. In a ki netic study, soya beans were toasted at 102, 120 and 134 degrees C for various durations (19 temperature/time combinations [T/t]), The raw a nd processed soya beans were measured for their functional lectins, tr ypsin inhibitor activity (TIA), urease activity (UA) and protein dispe rsibility index (PDI). The raw soya beans contained 7638 mu g g(-1) fu nctional lectins, 23.44 mg g(-1) TIA, 2.22 UA (Delta pH) and 85.7% PDI . These criteria all decreased as the heating time increased. Of all c riteria measured, the level of functional lectins was found to be most effectively inactivated by high temperature. In the second experiment , 35 piglets of approximately 30 kg liveweight were used, The animals were fitted with a post-valvular T-caecum (PVTC) cannula and divided i nto seven groups, which were fed a control diet and six experimental d iets, The diets consisted of 80% control diet and 20% processed soya b eans which were treated under the following conditions: 102 degrees C for 10 min, 102 degrees C for 20 min, 102 degrees C for 40 min, 120 de grees C for 2 min, 120 degrees C for 7.5 min and 134 degrees C for 1.5 min. The apparent ileal digestibilities of the soya beans processed i n these conditions [T/t] were: 37.0, 49.1, 61.3, 48.2, 57.0 and 56.8%, respectively, for dry matter (DM); 51.1, 68.3, 81.2, 70.3, 82.0 and 8 2.2%, respectively, for nitrogen (N); 82.2, 84.1, 89.2, 89.6, 93.0 and 91.8%, respectively, for ether extract. The apparent digestibilities of DM and N increased as the level of antinutritional factors decrease d, It appears that a certain amount of energy is required to achieve t he inactivation of antinutritional factors, either by treatment at a h igh temperature for a short time (e.g. 134 degrees C for 1.5 min), or for a longer time at a lower temperature (e.g. 102 degrees C for 40 mi n). It was noticed that the residual TIA content of the processed soya beans was correlated to the variation in digestibility among the anim als, which indicates that there are considerable differences between i ndividual animals in their responses to the soya bean antinutritional factors.