The enzymatic hydrolysis reaction is carried out by means of enzymes that act as catalysts to break the glycosidic bonds. Instead of using acid to hydrolyse the freed cellulose into glucose, enzymes are use to break down the cellulose in a similar way. Bacteria and fungi are the good sources of cellulases, hemicellulases that could be used for the hydrolysis of pretreated lignocellulosics. The enzymatic cocktails are usually mixtures of several hydrolytic enzymes comprising of cellulases, xylanases, hemicellulases and mannanases.

1.1.2. Fermentation process

The hydrolysis process breaks down the cellulostic part of the biomass into glucose solutions that can then be fermented into bioethanol. Yeast Saccharomyces cerevisiae is added to the solution, which is then heated at 32oC. The yeast contains an enzyme called zymase, which acts as a catalyst and helps to convert the glucose into bioethanol and carbon dioxide. Fermentation can be performed as a batch, fed batch or continuous process. For batch process, the fermentation process might takes around three days to complete. The choice of most suitable process will depend upon the kinetic properties of microorganisms and type of lignocellulosic hydrolysate in addition to process economics aspects.

The chemical reaction is shown below:

C 6H12O6 Zymase 2C 2H 5OH 2CO2

(Glucos e) Catalyst (Bioethanol) Carbon dioxide