Over
the past two decades, birchwood and beechwood xylans have
been used as a popular substrate for the characterization of xylanases.
Recently, major companies have discontinued their commercial production.
Therefore, there is a need to find an alternative to these substrates.
Xylan extraction from Acacia sawdust resulted in 23.5% (w/w) yield.
The extracted xylan is composed of xylose and glucuronic acid residues
in a molar ratio of 6:1 with a molecular mass of ∼70 kDa. The
specific optical rotation analysis of extracted xylan displayed that
it is composed of the d-form of xylose and glucuronic acid
monomeric sugars. The nuclear magnetic resonance analysis of extracted
xylan revealed that the xylan backbone is substituted with 4-O-methyl glucuronic acid at the O2 position. Fourier transform
infrared analysis confirmed the absence of lignin contamination in
the extracted xylan. Xylanase from Clostridium thermocellum displayed the enzyme activity of 1761 U/mg against extracted xylan,
and the corresponding activity against beechwood xylan was 1556 U/mg,
which confirmed that the extracted xylan could be used as an alternative
substrate for the characterization of xylanases.
Sugarcane bagasse
(SB) and sugarcane trash (SCT) containing 30%
hemicellulose content are the waste from the sugarcane industry. Hemicellulose
being heterogeneous, more complex, and less abundant than cellulose
remains less explored. The optimized conditions for the pretreatment
of SB and SCT for maximizing the delignification are soaking in aqueous
ammonia (SAA), 18.5 wt %, followed by heating at 70 °C for 14
h. The optimization of hydrolysis of SAA pretreated (ptd) SB and SCT
by the Box–Behnken design in the first step of saccharification
by xylanase (
Ct
Xyn11A) and α-
l
-arabinofuranosidase
(
Ps
GH43_12) resulted in the total reducing sugar
(TRS) yield of xylooligosaccharides (TRS
(XOS)
) of 93.2
mg/g ptd SB and 85.1 mg/g ptd SCT, respectively. The second step of
saccharification by xylosidase (
Bo
GH43) gave the
TRS yield of 164.7 mg/g ptd SB and 147.2 mg/g ptd SCT. The high-performance
liquid chromatography analysis of hydrolysate obtained after the second
step of saccharification showed 69.6% xylan-to-xylose conversion for
SB and 64.1% for SCT. This study demonstrated the optimization of
the pretreatment method and of the enzymatic saccharification by recombinant
xylanolytic enzymes, resulting in the efficient saccharification of
ptd hemicellulose to TRS by giving 73.5% conversion for SB and 71.1%
for SCT. These optimized conditions for the pretreatment and saccharification
of sugarcane waste can also be used at a large scale.
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