These enzymes enable the cleavage of the acetic acid and phenolic acid units in
the xylan molecule. Moreover, the cleavage of acetyl, feruloyl, and p-coumaryl
groups from xylan is an important step in the cleavage of lignin. At the same time,
breaking down the ester bonds between hemicellulose and lignin contributes to the
resolution of lignin (Subramaniyan and Prema 2000).
The enzyme examples in this group obtained from different microorganisms are
included in Fig. 9.5 (Kuhad et al. 1997; Sunna and Antranikian 1997).
9.3.3.4 Mannan and Mannolytic Enzymes
Mannan is a compound that is present in bacteria, fungi, and yeasts (Singh et al.
2018). Besides being an essential part of hemicellulose, it is also a storage polysaccharide in the cell walls of the algal species and in the seeds of some plants (Kaihou
et al. 1993; Ojima 2013; Decker et al. 2017). Mannan can be found in four different
forms such as linear mannan, galactomannan, glucomannan, and
galactoglucomannan (Moreira and Filho 2008).
While the mannan which is a linear and water-soluble polysaccharide consists of
a linear ß(1!4) mannopyranose polymer, galactomannans consist of the galactose
residues that are α-1,6 linked to the mannan backbone (Mestechkina et al. 2000;
Chaubey and Kapoor 2001).
α-1,6 linked galactose side groups in the galactomannans prevent the pair-bond
among the adjacent polymers, which in turn allows a more amorphous structure that
holds the water and contributes to its water solubility (Van Zyl et al. 2010).
Essentially, glucomannan is a ß (1!4) linked polysaccharide that is present in the
root of the konjac plant (Amorphophallus konjac) and consists of slightly breanchedchain D-glucosyl and D-mannosyl backbone (Katsuraya et al. 2003). Furthermore, it
is known that the man:glc ratio in its structure is $1.6:1 (Cescutti et al. 2002).
Finally, the galactoglucomannans contain galactose residues that are α-1,6 linked
on D-glycosyl and D-mannosyl residues with the ratio 3:1:1 mannose:glucose:
galactose. Due to high polymerization, acetylated galactoglucomannans which constitute the most of hemicellulose in softwoods fulfill a structural function similar to
the xylans in hardwoods (Willför et al. 2003).
Mannanases
Mannan-degrading enzymes take part in the glycosyl hydrolases synthesized by
fungi and bacteria (Singh et al. 2018). Certain microorganisms producing
mannanase are given in Fig. 9.5 (Kuhad et al. 1997; Vijayalaxmi et al. 2013).
The main enzymes that catalyze the hydrolyzation of linear mannans and
glucomannans are as follows:
• β-Mannanase (EC 3.2.1.78)
• β-Mannosidases (EC 3.2.1.25)
• β-Glucosidases (EC 3.2.1.21) (Dhawan and Kaur 2007).
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the xylan molecule. Moreover, the cleavage of acetyl, feruloyl, and p-coumaryl
groups from xylan is an important step in the cleavage of lignin. At the same time,
breaking down the ester bonds between hemicellulose and lignin contributes to the
resolution of lignin (Subramaniyan and Prema 2000).
The enzyme examples in this group obtained from different microorganisms are
included in Fig. 9.5 (Kuhad et al. 1997; Sunna and Antranikian 1997).
9.3.3.4 Mannan and Mannolytic Enzymes
Mannan is a compound that is present in bacteria, fungi, and yeasts (Singh et al.
2018). Besides being an essential part of hemicellulose, it is also a storage polysaccharide in the cell walls of the algal species and in the seeds of some plants (Kaihou
et al. 1993; Ojima 2013; Decker et al. 2017). Mannan can be found in four different
forms such as linear mannan, galactomannan, glucomannan, and
galactoglucomannan (Moreira and Filho 2008).
While the mannan which is a linear and water-soluble polysaccharide consists of
a linear ß(1!4) mannopyranose polymer, galactomannans consist of the galactose
residues that are α-1,6 linked to the mannan backbone (Mestechkina et al. 2000;
Chaubey and Kapoor 2001).
α-1,6 linked galactose side groups in the galactomannans prevent the pair-bond
among the adjacent polymers, which in turn allows a more amorphous structure that
holds the water and contributes to its water solubility (Van Zyl et al. 2010).
Essentially, glucomannan is a ß (1!4) linked polysaccharide that is present in the
root of the konjac plant (Amorphophallus konjac) and consists of slightly breanchedchain D-glucosyl and D-mannosyl backbone (Katsuraya et al. 2003). Furthermore, it
is known that the man:glc ratio in its structure is $1.6:1 (Cescutti et al. 2002).
Finally, the galactoglucomannans contain galactose residues that are α-1,6 linked
on D-glycosyl and D-mannosyl residues with the ratio 3:1:1 mannose:glucose:
galactose. Due to high polymerization, acetylated galactoglucomannans which constitute the most of hemicellulose in softwoods fulfill a structural function similar to
the xylans in hardwoods (Willför et al. 2003).
Mannanases
Mannan-degrading enzymes take part in the glycosyl hydrolases synthesized by
fungi and bacteria (Singh et al. 2018). Certain microorganisms producing
mannanase are given in Fig. 9.5 (Kuhad et al. 1997; Vijayalaxmi et al. 2013).
The main enzymes that catalyze the hydrolyzation of linear mannans and
glucomannans are as follows:
• β-Mannanase (EC 3.2.1.78)
• β-Mannosidases (EC 3.2.1.25)
• β-Glucosidases (EC 3.2.1.21) (Dhawan and Kaur 2007).
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