Proteolysis of Alcohol-Treated Soybean Meal Proteins by Bacteroides ruminicola, Bacteroides amylophilus, Pepsin, Trypsin, and in the Rumen of Steers

Sodium dodecyl sulfate-gel electrophoresis and cation exchange chromatography were used to examine degradation of treated and untreated soybean meal protein fractions by Bacteroides amylophilus H18₁, Bacteroides ruminicola B₁4, pepsin, trypsin, and intraruminally. Soybean meal treatments consisted of 30% vol/vol isopropanol, 40% propanol, or 50% ethanol at 22°C or 70% ethanol at 80°C. Water-soluble protein fractions were applied to a hydroxylapatite column and eluted with a discontinuous phosphate gradient of .03 to .27 and then .27 to 1.0 M. The four protein fractions with the highest absorbance at 276 nm were dialyzed against distilled water prior to being subjected to enzymatic hydrolysis. Soybean meal treated with 40% propanol had the greatest reduction in absorbance of all effluents at 275 nm, followed by soybean meal treated with 50% ethanol or 30% isopropanol. Comparison of electrophoretic patterns over time showed that B. amylophilus H18₁, degraded protein subunits more rapidly than B. ruminicola B₁4 Protein subunits with the highest molecular weights were the most rapidly degraded by B. amylophilus H18₁, B. ruminicola B₁4, pepsin, and trypsin. Hydroxylapatite chromatography of omasal fluid from steers supplemented with untreated soybean meal or soybean meal treated with 70% ethanol at 80°C indicated that no detectable soluble glycinin or conglycinin escaped ruminal degradation.