ENZYMATIC HYDROLYSIS OF AGRICULTURAL LIGNOCELLULOSIC BIOMASS

Abstract

The yield, productivity and cost for the enzymatic hydrolysis of cellulose to glucose
are crucial for the production of second generation ethanol. In the first study we
have evaluated the activity of several commercial cellulolytic enzymes and a crude
extract of a local strain of Trichoderma viride. The load used was 15 U of
cellulase/gram cellulose and 90 U of cellobiase/gram cellulose. The hydrolysis was
carried out at 50o
C and pH 4,8 for 96 hours. The best cellulose hydrolysis yield of
58% was obtained with the cocktail formed of crude cellulases from T. viride
CMIT3.5 combined with Novozyme 188. This cocktail was used in the second study,
when alkaline-steam pretreated wheat straw and corn stover where hydrolyzed at pH
4,8 for 96 hours. The temperature was set at 50o
C and 40o
C. The hydrolysis at lower
temperature was tested for a future experiment of simultaneous hydrolysis and
fermentation. An enzymatic assay using glucose-6-phosphate dehydrogenase was
used to determine exclusively glucose, instead of wide-range sugar DNS assay.
Reporting to 100 grams of wet pretreated biomass, the following results were
obtained: 14.4 g% glucose for corn stover at 50o
C and 13,0 g% at 40o
C; 13,1 g%
glucose for wheat straw at 50o
C and 10.3 g% at 40o
C. Considering that wheat straw
contain 36.6% glucose-based carbohydrates, the hydrolysis yields are between
39.3% and 28.1%. Further studies, concerning the optimal parameters for cellulase
cocktail will be made.