Biomedical Engineering Reference
In-Depth Information
lignocellulose
cellulose
lignin
hemicellulose
CH
3
COOH
CHO
H
H
CHO
CHO
CHO
CHO
HO
H
OH
OH
H
H
OH
H
OH
HO
HO
H
HO
H
HO
H
HO
H
H
H
H
OH
HO
OH
OH
H
HO
H
OH
H
OH
H
OH
H
CH
2
OH
Phenolic
compounds
CH
2
OH
CH
2
OH
CH
2
OH
CH
2
OH
arabinose
xylose
mannose
galactose
glucose
O
CHO
O
HO
2
HC
O
CHO
COOH
furfural
Formic acid
HMF
levulinic
Fig. 11.1
Reaction in different levels in the lignocellulose pretreatment process and the formation
of inhibitor [
65
,
66
]
For different fermentation products, inhibitors are different. For xylitol pro-
duction with fermentation, there are usually monosaccharides, including xylitol,
xylose, glucose, and arabinose in hemicellulose hydrolysis. These sugars have
different impacts on fermentation to produce xylitol. In the process of hemicellulose
acidic hydrolysis, a certain content of acetic acid, furfural, phenols, and other toxic
substances is generated and can obviously inhibit the fermentation performance of
the hydrolyzate. A variety of metal ions and anions in the hydrolyzate can also
influence xylitol metabolism [
67
]. Acetic acid, formic acid, and furfural, which are
the main inhibitors in the hemicellulose acid hydrolyzate, can influence
Rhizopus
arrhizus
growth with xylose as a carbon source and subsequent fermentation with
glucose as a carbon source for fumaric acid production. Growth of
Rhizopus
arrhizus
is sensitive to the concentration of formic acid and furfural, while acetic
acid significantly inhibits subsequent acid-producing fermentation of
R. arrhizus
.
In seed medium, the concentration of acetic acid, formic acid, and furfural should
be controlled within 1.5, 0.5, and 0.5 g
L
1
, respectively [
68
].
11.3.2.2
Measuring Methods for Inhibitor
Measuring of inhibitor type and concentration is crucial for selecting strains,
determining inhibition degree, and removing inhibitor in the cellulose bioconversion
process.
(1) Weak acids
Usually, gas chromatography is applied to analyze organic acids such as acetic acid
and formic acid quantitatively. Liu et al. [
69
] used GC for quantitative analysis
