Biomedical Engineering Reference
In-Depth Information
mode and its metabolites. These substances are known as model compounds.
Veratryl alcohol (3,4-dimethylphenylcarbinol) is a typical model compound for the
study of the lignin ring-opening reaction. It is the secondary product of white-
rot fungus metabolism. It plays an important role in lignin degradation. Through
research, the mechanism of veratryl alcohol ring-opening was proposed, which is
significant for the investigation of the aromatic ring opening of lignin monomer.
Elegir used
-5 types of model compounds to investigate the degradation
of laccase to lignin substances and found that the laccase mediator system could
degrade phenolic lignin but not nonphenolic lignin. Choemaker proposed the
fraction mechanism of the
“
-
“
and
“
-1 dimer model compound. Model
compounds play an important role in the study of lignin degradation. It is worth
noting that model compounds are only a simulation of lignin. Because of the
complexity of the lignin itself, the conclusions drawn from the study of model
compounds cannot be directly used for lignin. However, on the other hand, what
cannot degrade the model compound also cannot degrade lignin.
“
-1 bond with the
“
11.3.7.2
Investigation of the Lignin-Degrading Process by Analysis
of the Degradation Products of Natural Lignin
(1) Separation and characteristics of hydrolysates from low molecular weight lignin
[
154
]
Low molecular weight lignin degradation products are extracted from straw treated
with the white-rot fungus
Panus conchatus
with ethyl acetate as the extraction
agent. Alkali with different strengths can further separate low molecular weight
phenols, low molecular weight acids, and the neutral substance component. The
low molecular weight phenolic compounds and low molecular weight acids are the
main components of low molecular weight lignin degradation products. Their yields
are 51.1 % and 34.4 %, respectively. The high yield of low molecular weight phenol
is an important characteristic of straw lignin degradation with white-rot fungi
Panus
conchatus
. Infrared spectroscopy and nuclear magnetic resonance spectra initially
demonstrate that the oxidation reaction is dominant in lignin biodegradation.
Spectroscopy of low molecular phenols showed that the oxidation reaction of the
lignin side chain generates aldehyde and
-carbonyl group. The spectrum of the
low molecular weight acids revealed that the C
'
-C
“
bond is oxidatively cleaved,
forming aromatic carboxyl in addition to oxidation of lignin side chain to acids. The
difference between structures of the two main components preliminarily showed
that they are products of different degradation phases for rice straw lignin.
'
(2) Structural characteristics of aromatic acids from the low molecular weight part
of the lignin degradation product [
155
]
The main compounds and structure of acidic components were analyzed by a color-
MS integration technique. Lignin in rice straw was degraded by the white-rot fungi
Panus conchatus
to obtain the low molecular weight part of lignin degradation
products. The results showed that most of this component is an aromatic compound.
