BLBS102-c09 BLBS102-Simpson March 21, 2012 11:15 Trim: 276mm X 219mm Printer Name: Yet to Come
190 Part 2: Biotechnology and EnzymologyCarbohydrasesCarbohydrases are a group of enzymes that catalyze the hydrol-
ysis or synthesis of polysaccharides. Examples include the amy-
lases that hydrolyze starch molecules, maltases that break down
maltose into glucose units, and lactases that degrade lactose into
galactose and glucose. Other examples include invertases that
hydrolyze sucrose into glucose and fructose, glucanases that
catalyze the hydrolysis of glucans, cellulases that break down
celluloses into low molecular weight cellodextrins, cellobiose,
and/or glucose. Carbohydrases are ubiquitous in nature and are
widespread in animals, plants, and microorganisms. For exam-
ple, the amylases, pectinases, chitinases, andβ-galactosidases
are all found in plants, animals, and microorganisms (bacteria,
fungi, and yeast). Microbial sources of commercially available
carbohydrases are bacteria (e.g.,B. licheniformis), various fungi
(e.g.,A. niger,A. oryzae, A. aculeatus, Trichoderma reesei), and
yeasts (e.g.,Kluyveromyces lactis,Saccharomyces cerevisiae).
They are also present in algae, e.g., marine algae.
Two types of carbohydrases may be distinguished based on
their modes of action as the endo- versus exo-carbohydrases.
The endo-hydrolases (e.g.,α-amylase) catalyze the cleavage
of the internal glycosidic bonds of carbohydrate molecules,
while the exo-hydrolases (e.g.,β-amylase) catalyze the hydrol-
ysis of carbohydrates by removing the maltose units from the
nonreducing end of complex carbohydrate molecules. Carbohy-
drases may also be classified into the starch-hydrolyzing types
and the nonstarch-hydrolyzing types. The starch-hydrolyzing
carbohydrases (amylases, glucanases) act on amylose and amy-
lopectin, and their principal applications are in the production of
glucose syrups, ethanol, as well as in baking and brewing. The
nonstarch-hydrolyzing carbohydrases are those that break down
polymers of hexoses other than amylose and amylopectin, e.g.,
cellulases, lactases, maltases, galactosidases, pectic enzymes,
invertases, chitinases, and fructosidases.Amylases, Glucanases, and PullulanasesSome of the more common carbohydrases and their uses in
the food industry are the amylases that are used in the starch,
alcoholic beverages, and the sugar industries. For example,
Novozymes produces a heat-stableα-amylase (known as ter-
mamyl) from a genetically modified strain ofB. licheniformis
for the continuous liquefaction of starch at high temperatures
(105–110◦C). This same heat-stable enzyme is used to liquefy
or “thin” starch during brewing and mash distillation. It is also
used in sugar manufacture to hydrolyze the starch in sugar cane
juice. Nonfood applications ofα-amylases include their use in
the textiles industry for de-sizing of fabrics and in detergent for-
mulations for the removal of starch-based stains from fabrics.
Amyloglucosidase (AMG) is a type of amylase that cleaves the
α-1,4- andα-1,6-glycosidic bonds and removes glucose units
from liquefied starch sequentially. The commercially available
AMG enzyme is derived from a strain of the fungusA. niger, and
it is used to produce sugar syrups from starches and dextrins.
Glucanases are a group of hydrolytic enzymes that cat-
alyze the cleavage of glucans into various glucose oligomers,trisaccharides (e.g., maltotriose and nigerotriose), disaccharides
(e.g., maltose, trehalose, and cellobiose), and the monosaccha-
ride glucose. The term glucans encompasses those carbohy-
drate compounds made up of repeating glucose units linked
together by glycosidic bonds. Examples of glucans include
amylose starch (withα-1,4-glycosidic bonds), cellulose (β-1,4-
glycosidic bonds), zymosan (β-1,3-glycosidic bonds), glyco-
gen (with bothα-1,4- andα-1,6-glycosidic bonds), amylopectin
starch (with bothα-1,4- andα-1,6-glycosidic bonds), and pullu-
lan (with bothα-1,4- andα-1,6-glycosidic bonds). They occur in
plants, animals, and microorganisms; in plants and fungi, in par-
ticular, they serve as structural, defense, and growth functions,
and as storage forms of chemical energy (Thomas et al. 2000).
Several microorganisms (fungi, bacteria (Kikuchi et al. 2005),
and yeasts (Abd-El-Al and Phaff 1968) produce glucanases that
enable them to digest glucans for use as nutrients and energy
source. Glucanases are also widespread in plants, e.g., in seed
plants (Elortza et al. 2003), rice (Thomas et al. 2000), tobacco
(Leubner-Metzger 2003), acacia (Gonz ́alez-Teuber et al. 2010),
and in animal tissues, e.g., the embryo of sea urchins (Bachman
and McClay 1996), nematodes (Kikuchi et al. 2005), mollusks
(Kozhemyako et al. 2004), crayfish (Lee et al. 1992), earthworms
(Beschin et al. 1998), shrimp (Sritunyalucksana et al. 2002),
and insects (Hrassnigg and Crailsheim 2005). Bacteria are used
industrially to produce glucanases for use in applications such
as brewing to break down glucans in barley, thereby facilitating
filtration and preventing clogging of filters.
Pullulanase (also known as “debranching enzyme”) is a spe-
cific glucanase that degrades pullulan, a carbohydrate made up
of repeating units of the trisaccharide maltotriose linked together
byα-1,6 glycosidic bonds. Depending on the nature of the glyco-
sidic bond cleaved, two types of pullulanases are distinguished.
The type I pullulanases cleave theα-1,6 bonds, while the type II
pullulanases hydrolyze both theα-1,4 andα-1,6 linkages. Pul-
lulanases are produced by bacteria (e.g.,B. cereus(Nair et al
2006) andKlebsiellasp. (Pugsley et al. 1986)), and they are also
found in plants (e.g., rice (Yamasaki et al. 2008), wheat (Liu
et al. 2009), maize (Dinges et al. 2003)).
By virtue of their capacity to break down glucans into glucose
and low molecular weight oligomers of glucose, glucanases and
pullulanases are used extensively in industry for the manufacture
of animal feeds, alcoholic (beer and wine) and nonalcoholic
beverages (tea, fruit pulps), baked goods (breads), leather, and
textiles, as well as for waste treatment, oil extraction, and in
detergents.
Various amylase mixes are used as multienzyme cocktails,
which are employed to hydrolyze carbohydrates. An example is
the product Viscozyme, produced and marketed by Novozymes
from the fungusA. aculeatus. Viscozyme is used widely in the
food industry to degrade nonstarch polysaccharides, including
branched pectin-like substances often associated with starch in
plant materials, thereby reducing the viscosity of such materials
to facilitate the extraction of useful products from plant materi-
als. This way, the enzyme can also make starches more readily
available for fermentation into various liquefied products.
Other carbohydrases available under various trade names for
food uses include a fungal amylase powder derived fromA.