6.3 Textile and Fiber Processing
Another area of application for alkaline active hemicellulases is in the textile and
associated industries. Cotton fibers are important textile input, and processing of
these fibers involves several steps. Scouring is one of the steps that involve removal
of noncellulosic materials from the cotton. The conventional scouring of cotton is
done at high pH and temperature, a process which is not only expensive but also
polluting. Moreover, the harsh scouring process affects the quality of the fiber. Thus,
it was imperative to look for economical and benign alternatives. With this impetus,
bioscouring, the enzyme-assisted scouring processes that alleviate the problems
related to the conventional process, has emerged as promising alternative
[173]. Xylanases have been successfully tried as cotton scouring agents [174–
176]. The results of these evaluation studies indicate that the use of xylanases as
bioscouring agents allows to reduce the concentration of NaOH, lower the treatment
temperature, and shorten the treatment duration. In addition to these advantages, the
xylanase treatment improves the quality of the fiber. Unlike the conventional
processing, the enzyme bioscouring does not compromise the fiber strength, while
it improves the fiber water absorption capacity, and this facilitates the spinning
process. Furthermore, the enzymatic treatment makes the fiber soft and smooth
[2, 177].
In a similar way to cotton fiber processing, alkaline active xylanases and
mannanases can be used to process other plant fibers. For instance, dried ramie
stems can be soaked with hemicellulases to recover intact long cellulose fibers
[178, 179]. Together with pectinases, hemicellulases have been used to degum
bast fibers such as hemp, flax, and jute [19]. Since the lignin does not undergo
oxidation (which often leads to darkening) during enzymatic treatment, a strong
bleaching step is not a necessity. Alkaline soaking is preferable as it facilitates the
removal of noncellulosic materials from the fiber and inhibits the growth of
cellulose-degrading fungi. Thus, the use of alkaline active hemicellulases is ideal
for these applications.
6.4 Xylo- and Mannooligosaccharides
Oligosaccharides are short-chain sugar molecules containing two to ten monosaccharide units. The XOS and MOS, which are, respectively, obtained from xylan and
mannan, have many applications as discussed above in Sect. 3. Although these
oligosaccharides can be produced through acid or enzymatic routes, the enzymatic
process is the most desirable route. The use of alkaline active xylanases and
mannanases in production of these interesting saccharides has advantages over that
of neutral or acid active enzymes, mainly due to the better solubility of the hemicelluloses in alkaline condition, a case demonstrated by Samanta et al. [180]. Moreover, since hemicelluloses are often extracted with alkaline extraction method, it
274
G. Mamo
Another area of application for alkaline active hemicellulases is in the textile and
associated industries. Cotton fibers are important textile input, and processing of
these fibers involves several steps. Scouring is one of the steps that involve removal
of noncellulosic materials from the cotton. The conventional scouring of cotton is
done at high pH and temperature, a process which is not only expensive but also
polluting. Moreover, the harsh scouring process affects the quality of the fiber. Thus,
it was imperative to look for economical and benign alternatives. With this impetus,
bioscouring, the enzyme-assisted scouring processes that alleviate the problems
related to the conventional process, has emerged as promising alternative
[173]. Xylanases have been successfully tried as cotton scouring agents [174–
176]. The results of these evaluation studies indicate that the use of xylanases as
bioscouring agents allows to reduce the concentration of NaOH, lower the treatment
temperature, and shorten the treatment duration. In addition to these advantages, the
xylanase treatment improves the quality of the fiber. Unlike the conventional
processing, the enzyme bioscouring does not compromise the fiber strength, while
it improves the fiber water absorption capacity, and this facilitates the spinning
process. Furthermore, the enzymatic treatment makes the fiber soft and smooth
[2, 177].
In a similar way to cotton fiber processing, alkaline active xylanases and
mannanases can be used to process other plant fibers. For instance, dried ramie
stems can be soaked with hemicellulases to recover intact long cellulose fibers
[178, 179]. Together with pectinases, hemicellulases have been used to degum
bast fibers such as hemp, flax, and jute [19]. Since the lignin does not undergo
oxidation (which often leads to darkening) during enzymatic treatment, a strong
bleaching step is not a necessity. Alkaline soaking is preferable as it facilitates the
removal of noncellulosic materials from the fiber and inhibits the growth of
cellulose-degrading fungi. Thus, the use of alkaline active hemicellulases is ideal
for these applications.
6.4 Xylo- and Mannooligosaccharides
Oligosaccharides are short-chain sugar molecules containing two to ten monosaccharide units. The XOS and MOS, which are, respectively, obtained from xylan and
mannan, have many applications as discussed above in Sect. 3. Although these
oligosaccharides can be produced through acid or enzymatic routes, the enzymatic
process is the most desirable route. The use of alkaline active xylanases and
mannanases in production of these interesting saccharides has advantages over that
of neutral or acid active enzymes, mainly due to the better solubility of the hemicelluloses in alkaline condition, a case demonstrated by Samanta et al. [180]. Moreover, since hemicelluloses are often extracted with alkaline extraction method, it
274
G. Mamo