Can the same steam pretreatment conditions be used for most softwoods to achieve good, enzymatic hydrolysis and sugar yields?

Wood chips from six different Douglas-fir trees and a representative Lodgepole pine were steam pretreated at a single pretreatment condition (200 °C 4% SO₂ 5 min) which had previously been shown to be effective for Spruce and Lodgepole pine chips. All of the softwood samples responded in a similar fashion with more than 60% of the cellulose hydrolysed after 72 h, at an enzyme loading of 20 FPU/g cellulose. However, when the enzyme loading was reduced to 5FPU, less than 27% of the cellulose was hydrolysed. When the steam pretreated substrates were subsequently delignified they were almost completely hydrolysed, at both high, 20 FPU/g cellulose (less than 12 h) and low, 5 FPU/g (within 72 h) enzyme loadings. Although optimized steam pretreatment could result in greater than 90% glucose recovery, in order to obtain complete hydrolysis of the cellulosic component at reduced enzyme loadings a delignification step will likely be required.