BLBS102-c09 BLBS102-Simpson March 21, 2012 11:15 Trim: 276mm X 219mm Printer Name: Yet to Come
9 Enzymes in Food Processing 187proteins, or as sweeteners or bulking agents in food products
(Cheetham et al. 1989).Cyclodextrin Glycosyl TransferaseCGTase is also known by names like cyclodextrin glucanotrans-
ferase and cyclodextrin glucosyltransferase. CGTases have been
characterized from various genera of bacteria, includingBacil-
lus,Klebsiella,Pseudomonas,Brevibacterium,Micrococus,and
Clostridium(Bonilha et al. 2006, Menocci et al. 2008). CG-
Tases are known to catalyze at least four different reactions;
namely coupling, cyclization, disproportionation, and hydrol-
ysis. The most important of these reactions is intramolecular
cyclization, whereby linear polysaccharide chains in molecules
such as amylose are cleaved, and the two ends of the result-
ing fragments joined together to produce cyclic dextrins or cy-
clodextrins or CDs for short. CDs with varying units of glucose
that are linked together byα(1"4) glycosidic bonds have been
described, namely the 6 glucose CD (orα-CD), the 7 glucose
CD (orβ-CD), and the 8 glucose CD (orγ-CD). By virtue of
their ringed structures, CDs are able to trap or encapsulate other
molecules to form inclusion composites with altered physico-
chemical properties that have great potential for applications in
the (functional) foods, cosmetics, and fine chemicals (Shahidi
and Xiao-Qing 1993).AmylomaltaseThe enzyme amylomaltase, also known as 4-α-
glucanotransferase, catalyzes the transfer of glucans from
oneα-1,4-glucan to anotherα-1,4-glucan or to glucose. The
amylomaltase enzyme has been found in microorganisms, e.g.,
Clostridium butyricum, E. coli, S. pneumonia(Goda et al.
1997, Pugsley and Dubreuil 1988, Tafazoli et al. 2010) and
in plants, e.g., potato (Jones and Whelan 1969, Str ̈ater et al.
2002) and barley (Yoshio et al. 1986). The enzyme acts on
both malto-oligosaccharides and amylose to form medium to
highly polymerized cycloamyloses that are highly water-soluble
(Takaha et al. 1996, Terada et al. 1997). These products are also
expected to be of use in the (functional) food, pharmaceuticals,
and fine chemical industries.TransglutaminaseTGases are transferase enzymes that catalyze the acyl trans-
fer reactions between free amino groups furnished by−NH 2
groups (e.g., theε-NH 2 group of lysine) of amino acids and pro-
teins, and theγ-carboxyamide groups of glutamines (Motoki
and Seguro 1998). The TGase-assisted acyl transfer results in
the extensive formation of strong and resistant covalent bonds
between biomolecules like proteins. The products formed in-
variably have altered properties in terms of mechanical strength
and solubility in aqueous systems. This feature of the enzyme
is exploited in commercial food processing to improve the tex-
ture of gluten-free breads for individuals suffering from celiac
disease (Moore et al. 2004, 2006), for making imitation crab-meat and fish balls, and for binding small pieces of meat into
larger chunks of meat. The enzyme is also used as a binding
agent to improve the physical qualities (e.g., texture, firmness,
and elasticity) of protein-rich foods such as surimi or ham, and
emulsified meat products, such as sausages and hot dogs. They
are also used to improve the texture of low-grade meats such as
the so-called pale, soft, exudative meat or PSE meats; to improve
the consistency of dairy products (milk and yogurt) to make them
thicker and creamier; and to make noodles firmer (Kim and Kim
2009). TGases have been found to be present in animals (e.g.,
threadfin bream, big-eye snapper, white croaker (Benjakul et al.
2010), guinea pig (Huang et al. 2008), in birds, amphibians, and
invertebrates (Lantto et al. 2005), and in plants and microorgan-
isms (e.g.,Bacillus,Streptoverticullium,andStreptomycesspp
(Yokoyama et al. 2004).ProteasesThe term protease is used to represent the group of enzymes that
catalyze the cleavage of peptide bonds in proteins and peptide
molecules with the participation of water as co-reactant. Other
names for this group of enzymes include proteinases or prote-
olytic enzymes. The majority of industrial enzymes currently in
use are proteases, and it is estimated that they constitute about
40% of the total global enzyme production and use (Layman
1986, Godfrey and West 1996). These enzymes are used in
the food processing, animal feed, detergent, leather and textiles,
photographic, and other industries (Kalisz 1988). Proteolytic en-
zymes are also used as a digestive aid to facilitate digestion and
use of proteins by some people who otherwise cannot readily
digest these molecules.
On the basis of their mode of action on the protein/peptide
molecules, proteases are classified as either endopeptidases (or
endoproteases) or exopeptidases (or exoproteases). Endopepti-
dases are those proteases that cleave peptide bonds randomly
within protein molecules to result in smaller peptides. Exam-
ples include trypsin, chymotrypsin, pepsin, chymosin, elastase,
and thermolysin. Exopeptidases cleave peptide bonds by suc-
cessively removing terminal amino acid residues to produce
free amino acids and the residual polypeptide molecule. Thus,
two types of exoproteases are distinguished, the carboxypep-
tidases, that is, those that cleave amino acids at the carboxyl
or C-terminal of the protein or polypeptide molecule, and
the aminopeptidases that cleave amino acids from the amino
or N-terminal of the molecule. Examples of carboxypepti-
dases include depeptidase, cathepsin A, cathepsin C, metallo-
carboxypeptidases (e.g., carboxypeptidases A, A2, B, and C),
and angiotensin-converting enzyme; examples of aminopepti-
dase are glutamyl aminopeptidase (a.k.a. aminopeptidase A),
arginyl aminopeptidase (also known as aminopeptidase B), ala-
nine aminopeptidase, leucine aminopeptidase, and the methion-
ine aminopeptidases 1 & 2 (also known as METAP 1 & 2).
Proteases are traditionally classified into four sub-groups
based on the nature of their active sites as acid, serine, sulfhydryl,
and metallo-proteases. Their distinctive features are summarized
in the following subsections.