Electrophoretic analysis of ruminal degradability of corn proteins.

Albumin, globulin, and prolamin fractions were extracted from corn meal in water, .5 M NaCl, and 50% (vol/vol) 1-propanol and examined by SDS-PAGE and densitometric scanning to investigate fractional degradation rates of corn proteins. Several protein fractions were identified for globulins, zein prolamins, and glutelins. Ruminal degradability of individual subfractions was evaluated by suspension of corn and corn gluten meal samples in the rumen of lactating dairy cows from 0 to 72 h. Electrophoretic and densitometric analysis of protein residues revealed that the prolamin fraction zein for corn and corn gluten meal was more resistant to ruminal degradation than albumins, globulins, and glutelins. Relative rates of degradation of zein and the fraction containing albumins, globulins, and glutelins were .060, .026, and .018, .015/h for corn and corn gluten meal, respectively. Total degradabilities of corn and corn gluten meal, measured by summation of degradability of subfractional components, were 52.2 and 18.6%. Quantitative measurement of ruminally degradable subfractions and estimation of their degradation rates by electrophoretic and densitometric scanning are useful in understanding ruminal degradability of corn proteins.