renewable resources has made cellulases to be exploited for
producing fermentable sugars in cellulose biorefinery
(Kuhad and Gupta 2011).
iii. Hemicellulases: This group of enzymes integrates
a-arabinofuranosidases, a-glucuronidases, mannanases, and
a-d-galactosidases that attack the b-1,4-glycosidic bonds of
hemicellulose in lignocellulosic biomass. Hemicellulases are
efficient in breaking esterified side chain groups as well as
glycosidic bonds.
Mannanases destroy mannan which is the basic part of
the plant cell wall commonly in plant seeds and fruits. The
group of enzymes included in mannanases is b-mannanases,
b-mannosidases, and b-glucosidases (Malgas et al. 2015;
Chauhan et al. 2012). Mannan plays an essential role as seed
storage compounds and in an arabidopsis mutation where
(gluco)mannan synthase lacks (Malgas et al. 2015; Goubet
et al. 2003). Bacillus sp., Aspergillus sp., Clostridium sp.,
Streptomyces sp., Trichosporonoides oedocephalis, etc.,
have the ability to produce mannanases. They use apple
pomace, plantain peels, mango peels, potato peels, passion
fruit peel, etc., as substrates for mannanase production.
Mannanases are applicable in industries like pharmaceutical,
pulp and paper, food, oil, feed, textile and detergent industries, and coffee extraction (Chauhan et al. 2012).
iv. Pectinases: This includes a group of enzymes such as
pectinesterase, polygalacturonase, pectin lyase, and pectate
lyase which hydrolyze pectin. Pectin is a kind of polysaccharide which gives rigidity and structure and is present in
the primary cell walls and middle lamella of plants. These
classes of enzymes are most commonly used for the production and clarification of fruit juices. Pectinases can be
produced from wastes of strawberry pomace, orange peel,
cranberry pomace, apple pomace, citrus peel, sugarcane
bagasse, etc., when used as a substrate by Aspergillus niger
strains (Dhillon et al. 2004; Ahmed et al. 2016). Some
pectinase-producing microbes are Aureobasidium sp., Candida sp., Cryptococcus sp., Klebsiella sp., Kluyveromyces
sp., Penicillium sp., Bacillus sp., Pseudomonas sp., Rhizopus sp., Rhizomucor (Amin et al. 2019). Pectinases are being
exploited in wine industries, paper and pulp industries,
wastewater treatment, bioethanol production, extraction of
DNA from a plant, and protoplast isolation from a plant. In
addition, pectinases are expended in the production of animal feed, saccharification and liquefaction of biomass, oil
extraction, bio-scouring of cotton fiber, retting and degumming of plant fiber, and tea and coffee fermentation (Kubra
et al. 2018; Kashyap et al. 2001). Moreover, pectinases are
also used in feed to remove all the antinutritional properties
of pectin, augment the viscosity of plant products, and
progress digestion in animals (Ajila et al. 2012).
v. Xylanase: Xylanases are a complex and very important
group of carbohydrolases. This enzyme group consists of
a-glucuronidase, ferulic acid esterase, endo-xylanases,
b-xylosidases, p-coumaric acid esterase, and acetyl xylan
esterase which breakdown xylan (an important plant
polysaccharide) (Beg et al. 2001). Orange discards, apple
pomace, sorghum straw, lemon pomace, pear peel, lemon
peel, banana peel, soya bean hull, melon peel, and hazelnut
casing are used to produce xylanase by Trichoderma harzianum (Seyis and Aksoz 2005; Couto 2008), and grape
pomace used as substrate by Aspergillus niger to produce
xylanase (Teles et al. 2019). Xylanases are employed in
animal feed industries, food like bread and biscuit industries,
wine and beer industries, textile and paper industries, biofuel
production, deinking of waste paper. Some of
xylanases-producing microorganisms are Arthrobacter,
Micrococcus,
Bacillus, Paenibacillus, Staphylococcus,
Streptomyces, Nonomura, Flavobacterium, Cellulomonas,
Chaetomium thermophilum, Humicolainsolens, Thermoascus
auranticus,
Actinomadura,
Microbacterium,
Rhodothermus, and Pseudoxanthomonas (Alokika 2019;
Chakdar et al. 2016). Xylanase together with pectinase and
cellulase are commonly used in extracting and clarifying
fruit juices and liquefaction of fruits and vegetables (Alokika
2019). Similarly, xylanase with phytase and cellulase in
animal feed enhance digestion and absorption of nutrients
and xylanase with cellulase and laccase are applied to generate ethanol (Chakdar et al. 2016).
Enzymes Acting on Proteins
i. Proteases: These enzymes are the proteolytic enzymes that
break down peptide bonds between amino acids in
polypeptide chains. Proteases are one of the frequently significant industrial enzymes used in detergent, food, pharmaceutical, leather, textile, and silk industries. Based on the
catalytic residues in the functional site, proteases are
sub-categorized into metalloproteases, serine proteases,
cysteine proteases, glutamic acid proteases, aspartic proteases, and threonine proteases (Singh et al. 2016). Bacillus
sp. like B. licheniformis, B. lentus, B. amyloliquefaciens, are
the most exploited in the industrial sector for protease production (Razzaq et al. 2019). Aspergillus sp., Serratia liquefaciens, Flavobacterium balustinum, Penicillium sp.,
Rhizomucor sp., Rhizopus sp., Thermoascus aurantiacus,
Trichoderma reesei, etc., are also the proteases producers
(Singh et al. 2016). Proteases formed by Conidiobolus
coronatus, Streptomyces avermectnus, and Bacillus subtilis
are used in photographic industries to retrieve silver (Razzaq
et al. 2019). Plant also produces proteases which are broadly
consumed in food industries and medicine. The varieties of
plant proteases (bromelain, papain, ficin) are used in milk
clotting, brewing, cancer treatment, meat softening, viral and
digestion disorders (González-Rábade et al. 2011). FVWs
like jackfruit seed powder, palm kernel cake, olive oil,
152
S. Shrestha et al.
producing fermentable sugars in cellulose biorefinery
(Kuhad and Gupta 2011).
iii. Hemicellulases: This group of enzymes integrates
a-arabinofuranosidases, a-glucuronidases, mannanases, and
a-d-galactosidases that attack the b-1,4-glycosidic bonds of
hemicellulose in lignocellulosic biomass. Hemicellulases are
efficient in breaking esterified side chain groups as well as
glycosidic bonds.
Mannanases destroy mannan which is the basic part of
the plant cell wall commonly in plant seeds and fruits. The
group of enzymes included in mannanases is b-mannanases,
b-mannosidases, and b-glucosidases (Malgas et al. 2015;
Chauhan et al. 2012). Mannan plays an essential role as seed
storage compounds and in an arabidopsis mutation where
(gluco)mannan synthase lacks (Malgas et al. 2015; Goubet
et al. 2003). Bacillus sp., Aspergillus sp., Clostridium sp.,
Streptomyces sp., Trichosporonoides oedocephalis, etc.,
have the ability to produce mannanases. They use apple
pomace, plantain peels, mango peels, potato peels, passion
fruit peel, etc., as substrates for mannanase production.
Mannanases are applicable in industries like pharmaceutical,
pulp and paper, food, oil, feed, textile and detergent industries, and coffee extraction (Chauhan et al. 2012).
iv. Pectinases: This includes a group of enzymes such as
pectinesterase, polygalacturonase, pectin lyase, and pectate
lyase which hydrolyze pectin. Pectin is a kind of polysaccharide which gives rigidity and structure and is present in
the primary cell walls and middle lamella of plants. These
classes of enzymes are most commonly used for the production and clarification of fruit juices. Pectinases can be
produced from wastes of strawberry pomace, orange peel,
cranberry pomace, apple pomace, citrus peel, sugarcane
bagasse, etc., when used as a substrate by Aspergillus niger
strains (Dhillon et al. 2004; Ahmed et al. 2016). Some
pectinase-producing microbes are Aureobasidium sp., Candida sp., Cryptococcus sp., Klebsiella sp., Kluyveromyces
sp., Penicillium sp., Bacillus sp., Pseudomonas sp., Rhizopus sp., Rhizomucor (Amin et al. 2019). Pectinases are being
exploited in wine industries, paper and pulp industries,
wastewater treatment, bioethanol production, extraction of
DNA from a plant, and protoplast isolation from a plant. In
addition, pectinases are expended in the production of animal feed, saccharification and liquefaction of biomass, oil
extraction, bio-scouring of cotton fiber, retting and degumming of plant fiber, and tea and coffee fermentation (Kubra
et al. 2018; Kashyap et al. 2001). Moreover, pectinases are
also used in feed to remove all the antinutritional properties
of pectin, augment the viscosity of plant products, and
progress digestion in animals (Ajila et al. 2012).
v. Xylanase: Xylanases are a complex and very important
group of carbohydrolases. This enzyme group consists of
a-glucuronidase, ferulic acid esterase, endo-xylanases,
b-xylosidases, p-coumaric acid esterase, and acetyl xylan
esterase which breakdown xylan (an important plant
polysaccharide) (Beg et al. 2001). Orange discards, apple
pomace, sorghum straw, lemon pomace, pear peel, lemon
peel, banana peel, soya bean hull, melon peel, and hazelnut
casing are used to produce xylanase by Trichoderma harzianum (Seyis and Aksoz 2005; Couto 2008), and grape
pomace used as substrate by Aspergillus niger to produce
xylanase (Teles et al. 2019). Xylanases are employed in
animal feed industries, food like bread and biscuit industries,
wine and beer industries, textile and paper industries, biofuel
production, deinking of waste paper. Some of
xylanases-producing microorganisms are Arthrobacter,
Micrococcus,
Bacillus, Paenibacillus, Staphylococcus,
Streptomyces, Nonomura, Flavobacterium, Cellulomonas,
Chaetomium thermophilum, Humicolainsolens, Thermoascus
auranticus,
Actinomadura,
Microbacterium,
Rhodothermus, and Pseudoxanthomonas (Alokika 2019;
Chakdar et al. 2016). Xylanase together with pectinase and
cellulase are commonly used in extracting and clarifying
fruit juices and liquefaction of fruits and vegetables (Alokika
2019). Similarly, xylanase with phytase and cellulase in
animal feed enhance digestion and absorption of nutrients
and xylanase with cellulase and laccase are applied to generate ethanol (Chakdar et al. 2016).
Enzymes Acting on Proteins
i. Proteases: These enzymes are the proteolytic enzymes that
break down peptide bonds between amino acids in
polypeptide chains. Proteases are one of the frequently significant industrial enzymes used in detergent, food, pharmaceutical, leather, textile, and silk industries. Based on the
catalytic residues in the functional site, proteases are
sub-categorized into metalloproteases, serine proteases,
cysteine proteases, glutamic acid proteases, aspartic proteases, and threonine proteases (Singh et al. 2016). Bacillus
sp. like B. licheniformis, B. lentus, B. amyloliquefaciens, are
the most exploited in the industrial sector for protease production (Razzaq et al. 2019). Aspergillus sp., Serratia liquefaciens, Flavobacterium balustinum, Penicillium sp.,
Rhizomucor sp., Rhizopus sp., Thermoascus aurantiacus,
Trichoderma reesei, etc., are also the proteases producers
(Singh et al. 2016). Proteases formed by Conidiobolus
coronatus, Streptomyces avermectnus, and Bacillus subtilis
are used in photographic industries to retrieve silver (Razzaq
et al. 2019). Plant also produces proteases which are broadly
consumed in food industries and medicine. The varieties of
plant proteases (bromelain, papain, ficin) are used in milk
clotting, brewing, cancer treatment, meat softening, viral and
digestion disorders (González-Rábade et al. 2011). FVWs
like jackfruit seed powder, palm kernel cake, olive oil,
152
S. Shrestha et al.