Dry MG underwent a physical pretreatment through milling.
Milling decreases the particle size and the crystalline structure of
S. Prasertwasu et al. / Bioresource Technology 163 (2014) 152–159 153
MG, which results in an enhancement of surface area. The increase
of surface area allows MG to be further pretreated and digested
more easily (Quintero et al., 2011). After milling with a 60 mesh
sieving size, the size of the powdered MG was determined using
a particle size analyzer. According to Sluiter, the optimal size for
lignocellulosic biomass hydrolysis for ethanol production should
stay in between 20 and +80 mesh particle size. A larger mesh size
would cause inefficient hydrolysis of carbohydrates, and lead to
lower amount of sugar released. Alternatively, over-hydrolysis of
carbohydrates would occur if a smaller mesh size is used, resulting
in an increase of sugar degradation products (Sluiter and Sluiter,
2010). These degradation products may potentially cause detrimental
effects on fermenting yeasts as well as ethanol yield.