Biomedical Engineering Reference
In-Depth Information
on the UV spectrum. They found that 276 nm was the isosbestic point wavelength
for both furfural and HMF in concentrated acetic acid medium. In extract, acid-
soluble lignin is a major confounding factor. At the same time, acid-soluble lignin
is absorbed in a spectral range of 250-500 nm. However, furfural substances have
no absorption beyond 325 nm. The influence of acid-soluble lignin can be removed
by correcting the absorbance of acid-soluble lignin in the 325-nm wavelength.
Ultimately, the contents of furfural and HMF could be quantitatively detected by
a three-wavelength method based on the equal absorption wavelength of 276 nm,
furfural maximum absorption at 272 nm, and acid-soluble lignin in the wavelength
of 325 nm.
(3) Phenolic compounds
4-Hydroxy-benzoic acid, vanillin, and catechol are typical substances of phenolic
compounds that inhibit the fermentation process. In practice, the total phenolic
content is generally measured in solution.
Determination of the concentration of phenolic compounds [
73
] can use a
spectrophotometer for detection. Vanillin and tannin are taken as standards for
monophenol compound and polyphenol compound, respectively, to draw standard
curves. The determination method is to take 25 mL of the sample at 30
2
ı
C;
0.5 mL tannin-lignin reagent and 5 mL sodium carbonate-sodium tartrate reagent
are added into the sample quickly for 30 min. The absorption value is measured at
700 nm. The concentrations of monophenol compound and polyphenol compound
in the sample are obtained according to the absorbance values and the standard
curve of vanillin and tannin. Tannin-lignin reagent is prepared as follows: A 2,000-
mL flat-bottom flask is filled with 100 g of sodium tungstate (Na
2
WO
3
˙
2H
2
O), 25 g
of sodium molybdate (Na
2
MoO
4
2H
2
O), 700 mL of distilled water, 50 mL 85 %
H
3
PO
4
, and 100 mL of concentrated hydrochloric acid. The mixture is connected to
a reflux condenser and boiled for 10 h. Then, 150 g LiSO
4
, 50 mL of distilled water,
and a few drops of liquid bromine are added. The mixture is boiled for 15 min
to remove excess bromine. After cooling to 25
ı
C, the volume of the mixture is
set to 1,000 mL and filtered. The sample is kept under seal. Sodium carbonate-
sodium tartrate reagent is prepared as follows: 200 g of Na
2
CO
3
and 12 g sodium
tartrate (Na
2
C
4
H
4
O
6
2H
2
O) are put into 750 mL distilled water. The mixture is
heated to dissolve. Then, it is cooled to room temperature, and the volume is set
to 1,000 mL.
11.3.2.3
Inhibitor Removal Methods for Cellulose Bioconversion
As early as the 1940s, scientists discovered that the fermentation of a simple product
from cellulose dilute acid hydrolysis was not as simple as that of fermentable sugars.
There are certain fermentation-inhibiting substances in cellulose hydrolysates.
Therefore, the removal method of these substances began to be investigated. In the
past nearly six decades, a variety of biological, physical, and chemical methods
has been used to remove the inhibitors in cellulose hydrolysates to improve their
