Characterization of Protein Fractions in Fresh, Wilted, and Ensiled Alfalfa

¹ Department of Animal Science, University of British Columbia, Vancouver, BC, Canada V6P 1Z4
² Department of Food Science, University of British Columbia, Vancouver, BC, Canada V6T 1Z4
³ Agriculture Canada, Agassiz, BC, Canada V0M 1A0
⁴ Agriculture Canada, Kamloops, BC, Canada V2B 8A9

Fresh, wilted, and ensiled alfalfas were homogenized; the proteins were fractioned into total, soluble proteins precipitated at 40% ammonium sulfate concentration (fraction 2), soluble proteins recovered after extraction of fraction 2 (fraction 2B), and chloroplast membrane proteins (fraction 3). The fractions were analyzed by gel electrophoresis and assayed for sulfhydryl and disulfide content, dodecyl sulfate-binding capacity, and zeta potential. Wilting of alfalfa caused the loss of high molecular mass proteins, 49-kDa proteins of fraction 2 and 18- and 60-kDa proteins of fraction 3. Wilting alone did not affect proteins of fraction 2B but ensiling resulted in loss of five bands between molecular mass of 15 and 25 kDa. Ensiling wilted alfalfa resulted in loss of all proteins except small quantities of 22-, 33-, and 36-kDa proteins of fraction 2 and 15-, 28-, and 60-kDa proteins of fraction 3. Sulfhydryl and disulfides were increased during wilting and decreased by the ensiling process. Dodecyl sulfate-binding capacity was increased by ensiling, indicating that proteins in silage have a faster rate of enzymatic digestion. Soluble proteins had higher zeta potential than chloroplast membranes. Forage proteins surviving ensiling were albumins of fraction 2B and chloroplast membranes. These results indicate that alfalfa silage proteins are highly degradable in the rumen.

Key Words: characterization • alfalfa • proteins

Submitted on October 16, 1992
Accepted on February 1, 1993