Feed protein fractions in various solvents of ruminant feedstuffs

Abstract

The classical protein fractions, ie albumins, globulins, prolamins, glutelins and insoluble (or structural) proteins were evaluated in selected feedstuffs. Solvents used for classical protein fractionation were: dilute salt (1 M NaCl) in phosphate buffer (pH 7.0), aqueous alcohol (70% ethanol) and dilute alkali (0.05 M NaOH), with the subsequent separation of albumins and globulins by dialysis. In addition, crude protein content, soluble non-protein nitrogen, total true protein and soluble true protein in McDougall's buffer from the same feedstuffs were determined. The soluble non-protein N contributed only a small portion of the total N in feedstuffs. Total true protein was approximately 8-10% for energy feeds, and then increased to 30% for plant protein sources, while the soluble true protein was about the same for energy feeds and plant protein sources. The major proportion of protein in plant protein sources was in the form of globulins, followed by albumins and lessor amounts of glutelins and prolamins. In contrast, the major proportion of protein in cereals was in the form of prolamins and glutelins, followed by globulins and albumins.