Biomedical Engineering Reference
In-Depth Information
Fig. 1
Chemical structure and degradation of hemicellulose
2.2 Mechanism of Cellulose Biodegradation
The biodegradation of crystalline cellulose is slow because the substrate is insoluble
and poorly accessible to enzymes. The biodegradation mechanism of cellulose has
been studied over the last 50 years by scientists worldwide. EG, CBH, and bG have
been shown to act synergistically in this bioprocess, during which EG first randomly
cleaves the internal glycosidic bonds of the cellulose chain, and the resulting
exposed reducing or nonreducing ends are subsequently attacked by CBH, releasing
cellobiose, the substrate of bG, which eventually hydrolyzes cellobiose to glucose
(Fig. 2 )[ 24 ]. The optimized ratio of cellulolytic enzymes was investigated, and it
was found that the best saccharification of crystalline cellulose is achieved with an
enzyme blend (60:20:20 CBH I-CBH II-EG I) wherein a saturated level of bG was
included to eliminate cellobiose inhibition [ 25 ]. In a different report, the impact of
the cellulase mixture composition on cellulose conversion was modeled, and the
findings suggested different optimum ratios for substrates with different charac-
teristics, specifically degrees of polymerization (DP) and surface area [ 26 ]. These
theoretical and experimental conclusions, however, demand further examination, as
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