The effects of various deacetylation procedures on the nylon bag digestibility of barley straw and of grass cell walls recovered from sheep faeces

Abstract

SummaryTwo poorly digested materials, barley straw and grass cell wall residues recovered from sheep faeces, were treated with sodium ethoxide, methoxide or hydroxide under various conditions and the effects on their digestibilities studied by the nylon bag technique in the sheep rumen.Acetyl groups were removed during these treatments and the degree of deacetylation could be controlled by adjusting the amounts of reagents used, about 25 m-mole of base/g being required to produce the maximum effect. Sodium ethoxide in ethanol was the least effective of the reagents used: it did not remove acetyl groups from barley straw and left a larger proportion untouched in faeces cell walls than did sodium methoxide in methanol.Irrespective of the reagent employed digestibility increased with the progress of deacetylation and the two processes reached a maximum together, but there was not a linear relation between acetyl content and digestibility. In the case of straw treated with sodium hydroxide there appeared to be a linear relationship between digestibility and the amount of reagent applied, up to 20 m-moles/g straw.Phenolic ester groups were less susceptible to the reagents tested than acetyl groups. It is concluded that the action of the basic reagents is probably upon polysaccharides other than cellulose, that access to some regions of the cell walls may be limited by the solvent present, and that the linkages that restrict digestibility have a sensitivity to basic reagents similar to that of the acetyl ester groups present.