Deacetylation and enhancement of digestibility

The nylon bag technique has been used to study the effects of various reagents on the digestion of grass cell walls and straws in the sheep rumen. A large proportion of the acetyl groups were removed by sodium alkoxides in alcoholic solution with appreciable improvement in digestibility. Aqueous sodium hydroxide removed virtually all the acetyl, producing a correspondingly greater improvement.

When straw was treated with increasing amounts of sodium hydroxide, up to 10 g/ 100 g straw, the enhancement of digestibility was linear but not the release of acetyl; 2 g/100 g removed half the acetyl groups. After extraction with neutral detergent solution, followed by chlorite delignification, about 70% of the acetyl groups were left; sodium hydroxide treatment then had no effect upon the rate or extent of digestion of this residue.

Physical methods, based on X-ray diffraction and infrared absorption, showed that the degree of order of the cellulose component, which sets an upper limit to its rate of digestion, was not affected by concentrations of sodium hydroxide up to 20 g/100 g straw, more than sufficient to produce the maximum enhancement of digestibility.

Both electron micrography and chemical analysis indicated that the major components of the cell wall were removed simultaneously. It is concluded that the effects of basic reagents must be sought in the lignin-hemicellulose fraction of the cell wall, and that both covalent and hydrogen bonds may be responsible for its resistance to digestion.