RELEASE OF FREE FATTY-ACIDS FROM RAW OR PROCESSED SOYBEANS AND SUBSEQUENT EFFECTS ON FIBER DIGESTIBILITIES

Two in vitro experiments were conducted to determine the rates of lipo lysis and the extent of biohydrogenation of fat from raw or processed soybeans and to examine the subsequent effects on fiber digestibilitie s. In Experiment 1, substrates containing soy oil, raw soybeans, extru ded soybeans, and soybeans roasted at 132, 146, or 163 degrees C were incubated with ruminal contents for 2, 4, 6, 12, or 24 h; and release of FFA was measured. The FFA released from substrates containing soy o il, extruded soybeans, and raw or roasted soybeans reached maxima at i ncubations of 4, 6, and 12 h, respectively. As the roasting temperatur e increased from 132 to 163 degrees C, release of FFA decreased at inc ubations of 2, 12, and 24 h. Fatty acids in roasted soybeans were subj ected to less biohydrogenation than those in raw or extruded soybeans, suggesting that FFA of roasted soybeans are partially protected from ruminal bacteria. In Experiment 2, ground alfalfa hay was added to sub strates used previously to determine the effect of release rate of FFA on ADF and NDF digestibilities. At all incubation times, the substrat es containing soy oil and extruded soybeans had lower digestibilities, and those containing raw or roasted soybeans had higher digestibiliti es of NDF and ADF.