Scientific aspects of a diffuse straw digestion with dilute aqueous sodium hydroxide

Changes in chemical composition and morphology of wheat straw during a 5-step treatment with dilute aqueous sodium hydroxide of increasing (step 1 to 3) and then decreasing (step 4 to 5) NaOH concentration are described varying straw pretreatment, maximum NaOH concentration and total time of contact between straw and lye. These structural changes are correlated to increase in swelling, in-vitro degradability by cellulase and digestibility as revealed by feeding tests with sheep. Results are discussed on the basis of the processes of swelling, delignification and pentosan extraction, and the technological advantages of this multi-step treatment for enhancing the nutritional value of straw are discussed in comparison to a one-step treatment with subsequent lye-removal by pressing.