Stalk is composed of cellulose, hemicellulose, and lignin. Cellulose connects with hemicellulose and lignin with hydrogen bond, while hemicelluloses and lignin con­nects with each other by covalent bond. Therefore, the structure of cell wall is tight and complex. Cellulose, lignin, and hemicelluloses are composed of glucose, phenyl propane units, and pentose, respectively. It is obvious that three main component are different from each other. Cellulose and hemicellulose are carbohydrate, and lignin is aromatic.

Heterogeneous bioconversion property of stalk in component level presents in two processes: hydrolysis and fermentation.

In the hydrolysis process, hemicelluloses and cellulose could be hydrolyzed by cellulase. However, lignin is regarded as recalcitrance for cellulose enzymatic hy­drolysis [21]. On one hand, lignin prevents cellulase contacting to substrate. On the other hand, lignin absorbs cellulase non-productively.

In the fermentation process, glucose from cellulose could be used as the main carbon source. Pentose from hemicellulose could also be used by several microor­ganisms [8]. However, the hydrolysate of lignin, especially small molecular [22] is proved to be inhibitors for fermentation.

Therefore, if stalk is converted as a whole, cellulose conversion rate would be low because of lignin effect. It would be necessary to fractionate stalk into different components and then convert them, respectively.

For pulping, cellulose is extracted in pulping process with different chemicals pretreatment. However, lignin is removed to improve the property of pulp. Chemical structures of cellulose, hemicellulose, and lignin change differently during pulping.