Rice straw is composed of heterogeneous complex of carbohydrate
polymers. Cellulose (32-47%) and hemicellulose (19-27%) are densely packed
by layers of lignin(5-24%).
So it is necessary to have a pretreatment step to break lignin
seal to expose cellulose and hemicellulose for enzymatic action.
Pretreatment aims to decrease crystallinity of cellulose, increase
biomass surface area, remove hemicellulose, and break lignin seal.
Pretreatment makes cellulose more accessible to enzymes so that
conversion of carbohydrate polymers into fermentable sugars can
be achieved more rapidly and with more yields. Pretreatment includes
physical, chemical and thermal methods and their combinations.
Pretreatment has been viewed as one of the most expensive
processing steps in cellulosic biomass-to-fermentable sugars conversion
(Mosier et al., 2005).