corrosion problems as well as the high cost of acid consumption and recovery
present major barriers to economic success [2].
11 Enzymatic Hydrolysis
Hydrolysis catalyzed by enzymes that helps in favoring 100% selective conversion
of cellulose to glucose is known as enzymatic hydrolysis. This process is considered
to be a very slow process due to some factors like structural parameters of the
substrate, surface area, and the cellulose crystallinity. Utility cost of enzymatic
hydrolysis is low when compared to chemical hydrolysis technique since they are
usually conducted at mild conditions (pH 4.8) and temperature (318–323 K) and do
not produce corrosion. The enzymatic hydrolysis has resulted in high yields
(75–85%) with improvements being still developed. It is an environmentally friendly
process that involves enzymes like cellulases and hemicellulases to hydrolyze or
degrade the carbohydrates into fermentable sugars. Cellulose is typically hydrolyzed
by an enzyme called cellulase which is being produced by several microorganisms,
like bacteria and fungi. Cellulase is the most commercially used enzymes that
synergistically hydrolyze cellulose that involves synergistic actions by
endoglucanses, exoglucanases, and β-glucosidases. These enzymes together help
to hydrolyze intramolecular β-1, 4-glucosidic bonds present in the cellulose to
release soluble cellobiose or glucose and further hydrolyze cellobiose to glucose in
order to eliminate cellobiose inhibition. The different process factors affect the
enzymatic hydrolysis of cellulose, like the substrates chosen, cellulase activity,
reaction conditions (temperature, pH, as well as other parameters), and product
inhibition. Therefore, optimization of the hydrolysis process is necessary to improve
the yield and rate of enzymatic hydrolysis [2]. Three different enzymes present in
cellulase hydrolysis ß-1, 4 glucosidic linkages in the cellulose chains thus converting
them into simple sugars. Three steps involved in enzyme hydrolysis are shown in
Fig. 4.
Sindhu et al. [8] observed a fermentable sugar yield of 0.775 g/g under enzymatic
saccharification using 50 FPU cellulase enzyme with 11.25% w/w biomass loading
and 0.2% (Tween-80) surfactant concentration incubated at 50
C for 42 h. Sherpa
et al. [3] performed enzymatic hydrolysis under the conditions of 14% w/v biomass
loading and 19.33 IU/ml enzyme titer with pH maintained at 5 having an incubation
time of 7 h with temperature ranging from 45
to 55
C.
Maurya et al. [15] observed 0.376 g/g sugar yield under enzymatic hydrolysis
using cellulase enzyme with 10% w/w biomass loading, 0.04% surfactant concentration, and 100 FPU/g enzyme concentration incubating for 72 h. Srinorakutara
et al. [1] reported 0.509 g/g sugar yield with 15% w/w biomass loading and
50 FPU/g enzyme titer with pH 5 incubated for 48 h. Raghavi et al. [16] observed
0.796 g/g sugar yield under enzymatic hydrolysis using cellulase having 80 FPU/g
activity with 5% w/w biomass loading and 0.05% surfactant concentration incubated
for 24 h.
100
S. Niju and M. Swathika
present major barriers to economic success [2].
11 Enzymatic Hydrolysis
Hydrolysis catalyzed by enzymes that helps in favoring 100% selective conversion
of cellulose to glucose is known as enzymatic hydrolysis. This process is considered
to be a very slow process due to some factors like structural parameters of the
substrate, surface area, and the cellulose crystallinity. Utility cost of enzymatic
hydrolysis is low when compared to chemical hydrolysis technique since they are
usually conducted at mild conditions (pH 4.8) and temperature (318–323 K) and do
not produce corrosion. The enzymatic hydrolysis has resulted in high yields
(75–85%) with improvements being still developed. It is an environmentally friendly
process that involves enzymes like cellulases and hemicellulases to hydrolyze or
degrade the carbohydrates into fermentable sugars. Cellulose is typically hydrolyzed
by an enzyme called cellulase which is being produced by several microorganisms,
like bacteria and fungi. Cellulase is the most commercially used enzymes that
synergistically hydrolyze cellulose that involves synergistic actions by
endoglucanses, exoglucanases, and β-glucosidases. These enzymes together help
to hydrolyze intramolecular β-1, 4-glucosidic bonds present in the cellulose to
release soluble cellobiose or glucose and further hydrolyze cellobiose to glucose in
order to eliminate cellobiose inhibition. The different process factors affect the
enzymatic hydrolysis of cellulose, like the substrates chosen, cellulase activity,
reaction conditions (temperature, pH, as well as other parameters), and product
inhibition. Therefore, optimization of the hydrolysis process is necessary to improve
the yield and rate of enzymatic hydrolysis [2]. Three different enzymes present in
cellulase hydrolysis ß-1, 4 glucosidic linkages in the cellulose chains thus converting
them into simple sugars. Three steps involved in enzyme hydrolysis are shown in
Fig. 4.
Sindhu et al. [8] observed a fermentable sugar yield of 0.775 g/g under enzymatic
saccharification using 50 FPU cellulase enzyme with 11.25% w/w biomass loading
and 0.2% (Tween-80) surfactant concentration incubated at 50
C for 42 h. Sherpa
et al. [3] performed enzymatic hydrolysis under the conditions of 14% w/v biomass
loading and 19.33 IU/ml enzyme titer with pH maintained at 5 having an incubation
time of 7 h with temperature ranging from 45
to 55
C.
Maurya et al. [15] observed 0.376 g/g sugar yield under enzymatic hydrolysis
using cellulase enzyme with 10% w/w biomass loading, 0.04% surfactant concentration, and 100 FPU/g enzyme concentration incubating for 72 h. Srinorakutara
et al. [1] reported 0.509 g/g sugar yield with 15% w/w biomass loading and
50 FPU/g enzyme titer with pH 5 incubated for 48 h. Raghavi et al. [16] observed
0.796 g/g sugar yield under enzymatic hydrolysis using cellulase having 80 FPU/g
activity with 5% w/w biomass loading and 0.05% surfactant concentration incubated
for 24 h.
100
S. Niju and M. Swathika