BLBS102-c36 BLBS102-Simpson March 21, 2012 18:47 Trim: 276mm X 219mm Printer Name: Yet to Come
694 Part 6: Health/Functional FoodsThe hydrolytic reaction also depends on the availability of
susceptible bonds, on which the primary enzymic attack is con-
centrated, and on the physical structure of the protein molecule
(Raghunath 1993). Very little is known about the factors limit-
ing enzyme activity. The hypothesis explaining the downward
curvature could be related to one of the following phenomena:
a decrease in the concentration of peptide bonds available for
hydrolysis, enzyme inhibition, or enzyme deactivation. To ob-
tain more information about enzyme deactivation or inhibition,
the activity enzyme could be assayed during the course of hy-
drolysis, compared at the beginning and during the course of
the hydrolysis. A regular decrease in the areas observed during
the course of hydrolysis suggests an enzyme deactivation or an
enzyme inhibition by the inhibitory peptides, which are continu-
ously solubilized during hydrolysis. Such behavior also suggests
possible deactivation of the enzyme over the time due to a low
stability, including the possibility that the enzyme hydrolyzes
itself. This observation together with the results of the extra en-
zyme and substrate additions makes it possible to conclude that
the shape of the hydrolysis curves can be explained as a result
of the lack of peptide bonds available for hydrolysis combined
to a partial enzyme deactivation during the course of hydrolysis.Choices of SubstratesMuscle of different fish species have been used for the pro-
duction of protein hydrolysate such as capelin (Mallotus villo-
sus) (Amarowicz and Shahidi 1997), Atlantic salmon (S. salar)
(Kristinsson and Rasco 2000), mackerel (Scomber austriasi-
cus) (Wu et al. 2003), herring (Clupea harengus) (Sathivel et al.
2003), smooth hound (Mustelus mustelus) (Bougatef et al. 2009),
yellowstripe trevally (Selaroides leptolepis) (Klompong et al.
2007), red salmon (Oncorhynchus nerka) (Sathivel et al. 2005),
round scad (Decapterus maruadsi) (Thiansilakul et al. 2007),
tilapia (Oreochromis niloticus) (Raghavan et al. 2008), silver
carp (Hypophthalmichthys molitrix) (Dong et al. 2008), and
loach (M. anguillicaudatus) (You et al. 2009). Recently, tuna
dark muscle has been used for production of hydrolysate con-
taining antioxidative peptides (Hsu 2010). For some fish species,
their myofibrillar proteins were isolated as protein isolate prior
to enzymatic hydrolysis such as channel catfish (I. punctatus)
(Theodore et al. 2008). The protein isolate might be more prefer-
able for the proteinase used. As a consequence, hydrolysis could
take place at the higher degree, compared with that found in the
intact muscle. Moreover, oyster (C. gigas) protein (Qian et al.
2008b) and giant squid muscle (Rajapakse et al. 2005b) were
also used as source of protein hydrolysate with the antioxidative
activity.
By-products obtained from fish-processing plants have been
used for the preparation of protein hydrolysate with functional
properties and bioactivities. In general, a variety of proteases
have been used to cleave the protein, resulting in the peptides
with varying functional properties and bioactivity. By-products
(heads, viscera, frames, skin, trimmings) of black scabbardfish
(Aphanopus carbo) (Bougatef et al. 2010) and those (head and
viscera) from sardinella (Sardinella aurita) were used to produce
the protein hydrolysate. The frames from yellowfin sole (Junet al. 2004), Alaska ollack (Je et al. 2005c), and hoki (Joohnius
belengerii) (Kim et al. 2007) as well as backbones from tuna
(Je et al. 2007) and Atlantic cod (Gadus morhua)(Sliˇ zytˇ ̇eetal.
2009) have been used for the preparation of protein hydrolysates.
Apart from solid by-products, liquid effluent such as cooking
juice from tuna (Jao and Ko 2002, Hsu et al. 2009) have been
used as the raw material for hydrolysate production.
Protein hydrolysates were also prepared from gelatin ex-
tracted from aquatic animals. Gelatin hydrolysates with the an-
tioxidative activity have been produced from gelatin from the
skin of Alaska pollack (Kim et al. 2001), hoki (Mendis et al.
2005a), cobia (Yang et al. 2008), and sole (Gimenez et al.
2009). Furthermore, gelatin hydrolysates were also prepared
from the skin of jumbo squid (Mendis et al. 2005b), bullfrog
(Qian et al. 2008a), and squid (Gimenez et al. 2009). These
hydrolysates were mainly prepared with the aid of proteolytic
enzymes. Since gelatin can be hydrolyzed at high tempera-
ture, thermal hydrolysis was applied to produce the gelatin hy-
drolysate from cobia and tilapia skins (Yang et al. 2008, 2009a).
Recently, a protein hydrolysate from gelatin from the Nile
tilapia scale with the antioxidative activity was prepared by Ngo
et al. (2010).Microbial FermentationFermented fishery products are a good source of peptides and
amino acids, and rich sources of structurally diverse bioactive
compounds. Thus, fishery proteins are of particular interest due
to their high protein content and diverse physiological activi-
ties in the human organism. A great variety of naturally formed
bioactive peptides have been found in fermented fishery prod-
ucts. In fermented marine food sources, enzymatic hydrolysis
has already been carried out using microorganisms; thus, bioac-
tive peptides can be purified without further hydrolysis (Je et al.
2005b, Je et al. 2005d).
Proteolysis is an important biochemical process occurring
during fermentation. It is likely to be constituted by a very large
and complex group of enzymes, which differ in properties such
as substrate specificity, active site and catalytic mechanism, pH
and temperature optima, and stability profile. In general, en-
zymes important in fermentation may originate from four gen-
eral sources: (1) viscera and digestive systems, (2) muscle tissue,
(3) plant raw materials added to the fermentation, and (4) mi-
croorganisms active in the fermentation.
Proteolytic microorganisms play an important role during
fishery fermentation. There are several groups of microorgan-
isms that are well known for excretion of proteolytic enzymes
capable of degrading proteins. Many types of microbes excrete
proteolytic enzymes, includingAspergillus spp.,Bacillus spp,
halophilic bacteria, halotolerant and lactic acid bacteria (Mackie
et al. 1971, Lopetcharat et al. 2001). Careful selection by seeding
or controlling the growth environment within the fermentation
chamber enables the desired microbes to flourish and produce
significant quantities of proteolytic enzymes that help to hy-
drolyze the fish protein (Wheaton and Lawson 1985).
From our study, ACE inhibitory activity and antioxidative
activity of peptides extracted from various Thai traditional