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690 Part 6: Health/Functional Foodsactivity among the amino acids, followed by cysteine, histidine,
and phenylalanine, while histidine and hydrophobic amino acids
were suggested by Pena-Ramos et al. (2004) as the key factors ̃
in delaying lipid oxidation. Mendis et al. (2005b) reported that
the presence of nonaromatic amino acids such as proline, ala-
nine, valine, and leucine in jumbo squid skin hydrolysate con-
tributed to the higher antioxidative activities, and phenylalanine
and leucine residues atN-andC-terminals of peptide could
contribute to the high activity. Wang et al. (2008c) stated that
peptides exhibiting good antioxidative activity usually contain
certain amino acids such as histidine, proline, tyrosine and ly-
sine. Bougatef et al. (2010) indicated that peptides containing
histidine, tryptophan and tyrosine residues possessed antioxida-
tive activity. Guo et al. (2009) concluded that peptides contain-
ing tyrosine residues at theC-terminus, lysine or phenylalanine
residues at theN-terminus, and tyrosine residues in their se-
quences had strong free radical scavenging activity. Moreover,
Suetsuna et al. (2000) indicated that some other amino acids
such as proline, alanine, and leucine contribute to free radical
scavenging activity. Leucine and proline could favor antioxidant
activity when they occur at theC-terminus end of the sequence
(Suetsuna et al. 2000). In general, peptides containing tyrosine
tend to exhibit strong free radical scavenging activity due to
the phenolic hydroxyl groups, which contribute substantially to
scavenging activity toward free radicals via the mechanism of
donating a hydrogen atom from their hydroxyl group (Suetsuna
et al. 2000, Guo et al. 2009). Other aromatic amino acids, tryp-
tophan and phenylalanine, are generally considered as effective
radical scavengers, because they can donate protons easily to
electron deficient radicals while at the same time maintaining
their stability via resonance structures (Rajapakse et al. 2005b,
Zhang et al. 2009). In case of histidine-containing peptides, it is
thought to be connected to hydrogen-donating ability, lipid per-
oxy radical trapping, and/or the metal ion chelating ability of the
imidazole group (Mendis et al. 2005a, b). Hydrophobic peptides
can help in scavenging of free radicals by keeping close contact
with oxidizing substances leading to the rapid scavenging of
radicals (Mendis et al. 2005a, b). Some aromatic amino acids
and histidine are reported to play a vital role in the observed ac-
tivity. Gelatin peptides contain mainly hydrophobic amino acids
and abundance of these amino acids favors a higher emulsifying
ability. Hence, marine-gelatin-derived peptides are expected to
exert higher antioxidant effects among other antioxidant pep-
tide sequences (Mendis et al. 2005a). Therefore, marine-derived
bioactive peptides with antioxidative properties may have great
potential for use as nutraceuticals and pharmaceuticals and a
substitute for synthetic antioxidants.Antimicrobial ActivityAntimicrobial peptides (AMPs) have captured the attention of
researchers in recent years because of their efficiency in inhibit-
ing pathogens, bacteria, fungi, and virus. Adding preservative is
a common way of preventing or slowing microbial growth, the
major reason of food spoilage and poisoning. However, there
is a shortage of efficient and safe preservatives as a result of
appearance of resistant forms of food pathogens in response tomassive use of preservatives. Marine-derived AMPs are found
in a wide range of marine animals. These peptides are naturally
synthesized as a part of innate host defense mechanisms (Brown
and Hancock 2006) and may also be generated by enzymatic
hydrolysis of native proteins (Bulet et al. 2004, Liu et al. 2008,
Reddy et al. 2004). Among the marine animals, they are well
described in fish (Kitts and Weiler 2003, Hwang et al. 2010)
and the hemolymph of many marine invertebrates, including
spider crab (Stensvag et al. 2008), American lobster (Battison
et al. 2008), green sea urchin (Li et al. 2008), oysters (Liu et al.
2008), mussels, scallops, venerid clams and abalone (Cheng-
Hua et al. 2009), and shrimp (Destoumieux et al. 1997,Bartlett
et al. 2002). For example, the mudfish (Misgurnus anguillicau-
datus) produces a strongly basic peptide termed misgurin (Park
et al. 1997). This 2502 Da peptide contains five arginine and four
lysine residues and has antimicrobial activity against a broad
spectrum of microorganisms. The tissues of Atlantic salmon
(Salmo salar) contain an antimicrobial peptide with a molecular
mass of 20,734 Da. This purified peptide has been identified
as a histone protein and is termed histone H1 (Richards et al.
2001). Three antibacterial basic polypeptides, HLP-1, HLP-2,
and HLP-3 have been isolated from acetic extracts of channel
catfish (Ictalurus punctatus) skin (Robinette et al. 1998). The
molecular mass of these peptides were reported to be 15.5 kDa,
30 kDa, and 15.0 kDa, respectively. HLP-1 is the dominant pep-
tide and closely related to histone H2B, with inhibitory effects
against both fish bacterial pathogens andEscherichia coliD31.
Catfish (Parasilurus asotus) also contains a strong antimicrobial
peptide with the molecular mass of 2000 Da, named parasin I
consisting of 19 amino acids that include three arginine and five
lysine residues (Park et al. 1998). Because of high homology
toN-terminal sequence of histone H2A, parasin I may be de-
rived from histone H2A by a specific protease cleavage. These
AMPs have strong activity against gram-negative and gram-
positive bacteria as well as fungi. Potent antibacterial peptides
originating from pardaxin have been isolated from Moses sole
fish (Pardachirus marmoratus) (Shai 1994). Pardaxin is com-
posed of a helix-hinge-helix structure that is a common motif
found in many antibacterial and cytotoxic peptides. The peptide,
termed pleurocidin, is found specifically in the general epithe-
lial mucous cells of flounder and has an amphipathicα-helical
conformation enabling the binding to anionic phospholipid rich
membranes. In addition, two hydrophobic proteins with molec-
ular masses of 31 kDa and 27 kDa, respectively, have also been
isolated from skin mucous of carp (Cyprinus carpio)(Lemaitre
et al. 1996). In addition, marine-derived AMPs, such as urechis-
tachykinins, piscidins, and arenicin-1 exhibited significant an-
timicrobial activities against human microbial pathogens with-
out remarkable hemolytic effects against human erythrocytes
(Hwang et al. 2010).
Of marine invertebrates, antibacterial activity has been
reported in the hemolymph of the blue crab, Callinectus
sapidus,and it was highly inhibitory to gram-negative bacteria
(Edward et al. 1996). Although there are several reports on an-
tibacterial activity in seminal plasma, few antibacterial peptides
have been reported in mud crab,Scylla serrata(Jayasankar and
Subramonium 1999). The antimicrobial peptide derived from