African Journal of Biotechnology Vol. 8 (16), pp. 3893-3903, 18 August, 2009
Available online at http://www.academicjournals.org/AJB
ISSN 1684–5315 © 2009 Academic Journals
Ful Length Research Paper
The biochemical textural and sensory properties of
frozen stored (-22°C) king scallop (Pecten maxinus)
Aquaculture and Fisheries Department, Technological Educational Institute of Messolonghi, Nea Ktiria 30200,
Messolonghi, Greece. E-mail: email@example.com. Tel.:+302631058204. Fax: +302631058287.
Accepted 15 June, 2009
Post-rigor king scallop meats (Pecten maximus) were frozen individually for 24 h at -80°C and kept
vacuum packed at -22°C for up to 301 days. Sampling was carried out on fresh meats and at days 1, 28,
91, 154, 210 and 301 of frozen storage. Tests related to muscle integrity ( -hydroxy-acyl-coenzyme –A
dehydrogenase activities in muscle extracts), myofibrillar protein denaturation (Ca2+-ATPase activities
in actomyosin extracts) showed that storage time affected the integrity of muscles and caused
structural changes to myosin (or ‘actomyosin’). The water holding capacity (expressible fluids) of the
frozen stored scallop meats decreased with storage time and was associated with the denaturation of
myofibrillar proteins. The peak shear forces of frozen stored scallop meats, as measured by the Warner-
Bratzler shear knife, did not change with storage time, indicating that the length of time of storage at -
22°C did not affect the tenderness of the raw scallop meats. The storage time affected the sensory
attributes (flavour, texture and acceptability) of the frozen scallop meats, but these products were in
acceptable eating condition after a storage period of ten months. Ca2+-ATPase activities in actomyosin
extracts may be useful for assessing the quality loss of the frozen stored scallop meats, since a good
linear correlation was obtained with storage time and scores of sensory attributes.
Key words: Scal op meats, frozen storage, quality, enzymes.
Fresh fish are highly perishable commodities and are
from organel es and/or membranes may be more active
stored in ice until sold. The need for freezing of fish
than in the bound state (Hultin, 1985). The release of
arises when preservation by chil ing with ice is unsuitable
dehydrogenases from mitochondria might influence the
for the period of storage time involved (FAO, 1977). How-
redox potential of tissues and the release of lipases from
ever, freezing and storage of frozen fish may furnish
lysosomes may cause more rapid breakdown of lipids
favourable conditions for alterations in muscle structure,
(Shewfelt, 1981; Civera et al., 1996). The damage of
muscle proteins and lipids and textural properties in
organel es due to freezing and during storage can be
general. These changes are related to alterations in the
studied by the activities of enzymes in muscle tissue
sensory attributes of frozen fish and may affect their
fluids, enzymes that in fresh tissue are retained in intra-
market (Shenouda, 1980; Mackie, 1993).
cel ular organel es. The activity of the mitochondrial enzy-
Formation and growth of ice crystals during freezing
me -hydroxy-acyl-coenzyme A- dehydrogenase ( -HAD
and storage of fish may cause lysis of organel es and
H) has been regarded as a measure of the damage
disintegration of membranes. Enzymes that are released
caused in mitochondria by various freezing and thawing
treatments of meat and fish products (Gottesman and
Hamm, 1983; Makri et al., 2007).
Lipids that are liberated from the disintegrated mem-
branes could be subjected to faster hydrolytic or oxidative
dehydrogenase activity; TBARS, thiobarbituric acid reactive
reactions. The secondary oxidation products of lipids
substances; TCA, trichloroacetic acid.
influence directly the flavour or interact with proteins and
3894 Afr. J. Biotechnol.
cause off colours. The changes in lipids during storage of
At the laboratory, the scal ops were shucked and the striated part
frozen fish can be detected by a variety of chemical tests
of the adductor muscle, that is, the scal op meat, was separated
including free fatty acids content, peroxide value, conju-
from al other tissues. In order to ensure that the scal op meats
gated dines, thiobarbituric reactive substances (TBARS)
were in post rigor state, they were stored in glass jars without any
washing, buried in crushed ice and stored in a chil room at 2 to 4°C
etc (Shenouda, 1980).
for 3 days. Post-rigor scal op meats were required in order to en-
Changes in the moisture phase during freezing and
sure that any difference in instrumental texture measurements
frozen storage of fish may provide an environment that is
would indeed result from differences in freezing and frozen storage
conductive to changes in the myofibril ar proteins
and were not due to the development of rigor in the raw scal op
(Mackie, 1993). Alterations in myofibril ar proteins have
muscles prior to freezing. The mean weight of scal op meats was 35
been associated with the changes in water holding capa-
± 5.6 g (mean ± S.D.).
At the end of the storage period, the scal op meats were divided
city and textural properties of frozen stored fish. The
into 7 groups, each containing 15 scal op meats. The scal op meats
changes in myofibril ar proteins can be detected in the
from the first group were analyzed as unfrozen controls and the
form of reduced solubility and extractability in saline and
others were individual y frozen at -80°C for 24 h on perforated stain-
other extracting solutions and also reductions in myosin
less steel sheets. During freezing, the temperature of the centre of
and actomyosin ATP-ase activities, sulfhydryl groups, ap-
6 scal op meats was monitored using T -type thermocouples and a
recording thermometer (Comark Instruments, U.K.). Immediately
parent viscosity, gel-forming ability etc (Shenouda, 1980).
after freezing, the scal op meats were placed in polyethylene food
The physical, chemical, bio-chemical and sensory pro-
bags, each containing 5 frozen scal op meats. The bags were
perties of frozen stored fish species have been studied
vacuum-packed and stored in a domestic freezer cabinet at -22°C.
for several decades because of their economic importan-
The stored frozen scal op meats were analyzed for physical,
ce. However, little information is available on the quality
biochemical and sensory properties immediately after freezing and
of frozen stored bivalve mol uscs that comprise a signifi-
after 28, 91, 154, 210 and 301 days in frozen storage. In each
sampling period, 15 frozen scal op meats, that is, the content of 3
cant marine resource.
bags, were analyzed.
King scal op (Pecten maximus), a bivalve mol usc, is
Thawing of frozen scal op meats was performed by placing the
widely distributed in northwest Europe (Brand, 1991). It is
scal op meats individual y on a wire gauge set on top of a plastic
much prized as food and the adductor meat, the major
cup. The whole apparatus was enclosed in a plastic bag to prevent
edible part of king scal op, is offered to the consumers
evaporation and kept at +4°C in a refrigerator for 12 h. Subse-
mainly as fresh and frozen product (Hardy and Smith,
quently, sensory, expressible fluids and instrumental texture deter-
minations were performed on each frozen/thawed scal op meat.
1986). In addition, the exports of king scal ops from the
The remaining tissue from those determinations and a slice of
producer countries are based mostly on frozen products.
approximate weight of 2 g, which was removed from the right
For instance, the production of frozen scal ops in U.K. in
surface of each scal op meat were used for the preparation of the
the year 2004 accounted for 20% of the total production
extracts for the chemical and biochemical analyses, as fol ows (i)
of scal ops (FAO: http://faostat.fao.org). Freezing,
the slices from 5 scal op meats were used for the preparation of
one extract for the -hydroxy-acyl-coenzyme-A dehydrogenase
therefore, forms an important section of scal ops industry.
(HADH) determinations and (i ) the remaining tissues from 5 scal op
There are some reports in the literature on freezing and
meats were pooled first and then minced in a domestic mincer. The
cold storage of scal op species (Dyer and Hiltz, 1974;
minced scal op meats were then immediately used for the prepa-
Aurel et al., 1976; Chung and Merritt, 1991a, b;
ration of extracts.
Kawashima and Yamanaka, 1992, 1995 a,b; 1996), but
For the chemical and biochemical analyses, 3 extracts were pre-
there is a lack of information on the quality of frozen King
pared for each storage period coming from 5 different scal op
meats. The extracts were stored in an -80°C freezer until analysis.
scal op adductor meat. Therefore, the stability in storage
The results of the chemical and biochemical analyses were the
of king scal op adductor meat need to be investigated.
mean of 3 independent determinations and those of sensory,
The present study is aimed to investigate the effects of
expressible fluids and instrumental texture determinations were the
the length of time in frozen storage on the quality of
mean of 15 independent determinations.
scal op meats (P. maximus) in regard to the integrity of
muscle structure, myofibril ar protein denaturation, lipid
Freezing time and rate determination
degradation, instrumental texture and sensory changes.
The information obtained would be useful for assessing
The thermocouples for the temperature measurements were placed
the quality of king scal op meats during storage for com-
at the centre of the thickest part of the scal op meats which was
taken as the maximum distance between the right and the left
surface of the scal op meats, and was measured by using a vernier
instrument. The thermocouple was inserted at the centre of the
thickest part from the lateral surface of the scal op meat.
MATERIALS AND METHODS
The freezing time (te) was calculated as the time (minutes)
required to decrease the temperature of the thermal centre from an
Scallop meats processing and storage
average initial temperature of 4 ± 1°C to a final temperature of -
20°C fol owing the recommendations of the International Institute of
A total number of 105 whole scal ops (P. maximus), from the
Refrigeration (1986). The freezing rates at the thermal centre,
Orkney fishing area, were purchased from the Aberdeen fish mar-
expressed as cm h-1, were obtained from the ratios of the distance
ket. The whole live scal ops were delivered to the School of Life
from the surface to the thermal centre of the scal op muscles and
Sciences of the Robert Gordon University packed in crushed ice on
the effective freezing times, te (in hours; Chen and Pan, 1995) fol-
the same day as their arrival at the fish market.
lowing the formula
Freezing rate (cm h-1) = Half thickness of scal op muscle (cm) x t -1
using a Steven’s texture analyzer fitted with a cylindrical flat probe
(50 mm diameter and 20 mm height). The above-mentioned force
The characteristic freezing time (tc) was calculated according to
was chosen since it would cause the least possible damage to the
Bevilaqua et al. (1979) as the time (in min) for which the thermal
cylinders (Chung and Merritt, 1991a). Expressible fluids were
centre of scal op muscles was in the temperature range of maximal
calculated from the weight difference between the initial and the
ice crystal ization, that is from -1 to -7°C.
final weight of the cylinders. Two measurements per frozen stored
and thawed scal op meat were taken.
The results of expressible fluids determinations were expressed
Determination of the -hydroxy-acyl-coenzyme-A dehydro-
as g per kg of weight of frozen/thawed scal op meats.
genase activity of scallop meats
The filtrates for the HADH (enzyme class [EC] 1.1.35) assays were
Texture determination as measured by the texture analyzing
prepared according to Fernandez et al. (1999). The HADH released
in the filtrate was assayed according to Fernandez et al. (1999).
Results were expressed as mil iunits per gram of tissue.
Texture measurements were performed according to Chung and
Merritt, (1991b). Peak shear force measurements were performed
with a Steven’s texture analyzer at a crosshead speed of 50 mm
Ca2+- ATPase activities in actomyosin extracts
per min. Shear strengths were measured with a V-shaped Warner-
Bratzler shear probe mounted on the Steven’s load cel .
For the preparation of actomyosin, a portion (5 g) of the scal op
From the central part of each scal op meat 2 cylinder portions (10
meats’ mince was washed with 25 ml of ice-cold de-ionised water
mm in diameter and 10 to 15 mm long) were excised longitudinal to
for 15 min and drained through a chil ed Buchner No 3 funnel under
muscle fibres using a cork borer. Individual cylinders were weighed
vacuum. This step was needed to deplete the mince of sarcoplas-
and then inserted through the triangular opening of the blade and
mic proteins. It was repeated twice more.
placed on the load cel in such a position that the scal op meat
A volume of 20 ml of iced-cold 5% (w/v) NaCl (pH = 7) was
fibres were at right angles to the blade penetration. The peak shear
added to the washed mince. The slurry was al owed to stand at 0 to
force, expressed in gram-force (g*), required to cut the cylinder into
4°C for an extraction period of one hour and subsequently was
2 pieces was read from the control panel of the analyzer. The shear
centrifuged for 30 min at 5,000 g at 4°C. The supernatant solution
peak force was adjusted to units of g*per g of scal op meat cylinder
was designated ‘actomyosin extract’ and was used for protein con-
to take into account of variations in weight of scal op meats
tent and Ca2+-ATPase activity measurements.
cylinders (Chung and Merritt, 1991b).
The protein concentration in actomyosin extracts was determined
by the bicinchoninic acid (BCA) procedure (Sigma Procedure
TPRO-562, BCA-1, Sigma Biochemicals Co., St. Louis, Mo.,
The Ca2+-ATPase activity was determined according to Carvajal
A portion (4-5 g) of muscle was removed from the anterior part of
et al. (1999). A portion (100 l) of actomyosin extract was added to
each scal op meat longitudinal to muscle fibres. It was steam-
50 l of 0.5 M Tris-maleate (pH = 7). To that mixture were then
cooked for 10 min using a domestic steam cooker. After cooking,
added 50 l of 0.1 M calcium chloride, 750 l de-ionized water and
the portions of scal op meats were placed on wire gauze supported
50 ml 20 mM ATP solution (pH = 7). The reaction was conducted
on a plastic cup, the whole apparatus was covered with a
for exactly three minutes at 25°C and terminated by adding by
polyethylene bag and left at room temperature to cool for 30 min.
adding 0.5 ml of chil ed 15% (w/v) of trichloroacetic acid solution
The portions of scal op meats were then evaluated by 15 trained
(TCA). The mixture was then centrifuged at 10,000 g for 30 min and
assessors for flavour, texture and overal acceptability.
the inorganic phosphorus liberated in the supernatant was mea-
Flavour and overal acceptability were scored on a 5-point scale
sured by the method of Fiske and Subbarow (1925). Specific
and texture on a 6-point scale. The scoring system for flavour was
activity was expressed as moles inorganic phosphate (Pi) release-
as fol ow:
ed/mg protein/minute. A blank solution was prepared by adding
chil ed TCA prior to addition of ATP.
5 = normal sweet taste
4 = no sweet flavour, neutral
3 = slight sour or rancid flavour
Thiobarbituric acid reactive substances determinations
2 = moderately strong sour and rancid flavour
1 = very unpleasant putrid or rancid flavour
A portion (5 g) of the scal op meats’ mince was homogenized with
20 ml chil ed 7.5% (w/v) trichloroacetic acid (TCA) for 0.5 min and
The degree of liking (overal acceptability) was rated using a five
filtered using Whatman No 1 filter paper. A portion (0.5 ml) of this
point hedonic scale. The scale was as fol ows:
filtrate was used for the determination of thiobarbituric acid reactive
substances (TBARS, mg malondialdehhyde per kg of sample)
5 = like very much
according to Vyncke (1970).
4 = like
3 = neither like or dislike
2 = dislike
Determinations of expressible fluids
1 = dislike very much.
Two cylindrical portions of each scal op meat, 4 mm in thickness
For texture rating, the scoring system, described by Koning and Mol
and 20 mm in diameter, were excised from the left surface of
(1991) with slight modifications, was used. The scoring system was
scal op meats by means of a ring having 4 mm thickness and 20
as fol ow:
mm diameter. Each cylinder was weighed accurately with a Mettler
analytical balance and placed on a double thickness filter paper
5 =Tender, succulent, normal texture
Whatman No 1. It was then covered with another double thickness
4 = Slightly tough and dry
filter paper and the pack was subjected to a 1,000 g force for 1 min
3 = Tough, dry but edible
3896 Afr. J. Biotechnol.
Storage Time (days)
Figure 1. The effect of the length of time of storage at -22?C on -hydroxy-acyl-coenzyme-A dehydrogenase activities.
Values are means ± SEM, n = 3. Groups with different letters (a, b) are significantly different (P<0.05). The ‘0’ storage
time presents fresh scal op meats.
2 = Very tough and dry
Institute of Refrigeration, 1986). Therefore, the experi-
1 = Stringy, unable to swal ow
mental conditions of freezing scal op meats in the present
0 = Very stringy, completely inedible.
study produced freezing times and rates that can be met
in commercial practice of freezing scal op meats.
One-way analysis of variance (ANOVA) was performed to test for
Effect of storage time on -hydroxy-acyl-coenzyme-A
the effects of storage time on physical, chemical and biochemical
dehydrogenase activity in scallop meats
parameters. ANOVA based on Kruskal-Wal is method was used to
examine the effects of storage time on each sensory attribute, since
scoring was limited to discrete values. Pearson’s correlation co-
In fresh tissue the enzyme HADH is retained in mito-
efficients between the means of the parameters studied were also
chondria. However, HADH activities were found in the
calculated. The parametric and non parametric ANOVAs showing
filtrates of fresh scal op meats (Figure 1). These results
significant differences were fol owed by a Tukey HSD and Dunn
suggest that mitochondria were damaged at the surfaces
post-hock test, respectively. In al statistical analyses significance
where the scal op muscles were cut and thus a certain
was accepted when P < 0.05 (Zar, 1984).
amount of the enzyme had leaked from damaged mito-
chondria into the muscle (Gottesman and Hamm, 1983).
RESULTS AND DISCUSSION
Moreover, autolysis of the scal op meats could have
caused disruption of some mitochondria, since the fresh
The freezing process
scal op meats were stored in ice for 3 days prior to
analysis (Hoz et al., 1992, 1993; Pavlov et al., 1994).
Freezing scal op meats in a -80°C freezer produced
The activities of HADH in scal op meats frozen for 24 h
freezing times, freezing rates and characteristic freezing
at -80°C and then thawed were significantly higher than
times equal to 28 min, 3.17 cm/h and 19 min, respec-
those in fresh scal op meats (Figure 1). HADH activities
tively. In commercial fish industries, scal op meats are
have been reported to have increased due to freezing in
frozen mostly individual y in mechanical freezing systems
trout (Garcia de Fernando et al., 1992; Hoz et al., 1992),
(Mason, 1983; Hardy and Smith, 1986). Typical freezing
kuruma prawn (Hoz et al., 1993), sole, salmon, prawn,
rates that can be met by freezing of seafood by such
Norwegian lobster (Fernandez et al., 1999), plaice,
freezing systems range from 0.3 to 3 cm/h (International
whiting and mackerel (Dulfos et al., 2002). These findings
+ a oles P 0.15
Storage Time (days)
Figure 2. The effect of the length of time of storage AT -22?C on Ca2+-ATPase activities. Values are means ± SEM, n
= 3. Groups with different letters (a, b, c) are significantly different (P<0.05). The ‘0’ storage time presents fresh
scal op meats.
and the results of the present study indicate that the
cel ular ice formation (Love, 1955). Therefore, the addi-
freeze-thaw process itself affects the integrity of mito-
tional release of the HADH enzyme, observed in scal op
chondria of scal op meats. The freeze damage of mito-
meats stored for 91 days at -22°C, may be due to further
chondria may be due to dehydration of the mitochondrial
mechanical damage of mitochondrial membranes by the
inner membrane and/or mechanical disruption of mito-
enlargement of intra-cel ular ice and/or dehydration of
chondrial membranes by ice crystals (Hamm and
membranes by the formation and accretion of inter-
cel ular ice (Hamm and Gottesmann, 1982). Moreover,
From the results of the present study, an increase in
the decrease in HADH activity in scal op meats after 91
HADH activity in scal op meats was observed in the first
days of storage may be due to the denaturation of the re-
91 days of storage at -22°C, fol owed by a slight decrea-
leased enzyme during prolonged storage. Similar results
se up to 301 days (Figure 1). HADH activities in frozen
and suggestions were reported by Benjakul et al. (2003)
scal op meats stored frozen for 91 days were 7.3 times
after studying the effects of prolonged cold storage at -
the HADH activities of fresh scal op meats. In addition,
18°C on membrane integrity of croaker and lizardfish as
the HADH activities in the scal op meats, frozen for 24 h
determined by marker lysosomal enzymes.
at -80°C and then thawed increased about 4.5 times the
Overal , the time in cold storage at -22°C may affect the
activity of the fresh scal op meats. Thus, a part of the
integrity of intra-cel ular organel es of scal op meats via
release of HADH in frozen scal op meats, stored for 91
ice recrystal ization, it may also affect the activity of re-
days at -22°C, may be related to the time the scal op
leased mitochondrial enzymes.
muscles remained in frozen storage at -22°C and not only
to the freezing process. By means of lysosomal marker
enzymes, Benjakul et al. (2003) showed that storage over
Effects of storage time on Ca 2+-ATPase activities in
24 weeks at -18°C caused disintegration of membrane
structures of several tropical fish.
The storage of a frozen muscle at temperatures above
Ca2+-ATPaseactivity in actomyosin extracts from frozen
its eutectic temperature goes together with the growth of
stored frozen scal op meats decreased throughout the
intra-cel ular ice and formation and accretion of inter-
301 days of frozen storage at -22°C. The marked de-
cel ular ice (Hamm, 1986). In the present study, scal op
crease was observed within the first 91 days of frozen
meats were frozen at characteristic freezing time (tc
storage (Figure 2).
value) of 19 min, which should, mainly, result in intra-
The decrease in Ca2+-ATPase activities in actomyosin
3898 Afr. J. Biotechnol.
Storage Time ( days)
Figure 3. The effect of the length of time of storage at -22?C on thiobarbituric acid reactive substances (TBARS).
Values are means ± SEM, n = 3, ns = not significant. The ‘0’ storage time presents fresh scal op meats
extracts during extended frozen storage of scal op meats
Effects of storage time on thiobarbituric acid reactive
could indicate conformational changes (unfolding) and
aggregation of the head region of myosin (or ‘acto-
myosin’), which contains the active site of the enzyme.
From the results of the present study, TBARS did not
Re-arrangements of protein via protein -protein interac-
change significantly during storage of frozen scal op
tions might have contributed also to the loss in AT Pase
meats at -22°C. However, TBARS reached a maximum
activity. These changes in myosin (or ‘actomyosin’) might
up to 91 days of storage and then decreased (Figure 3).
have been caused by the increased salt concentration in
Changes in TBARS during cold storage have been
the unfrozen phase of scal op meats as a consequence
studied in chub mackerel and smooth hound (Vareltzis et
of ice re-crystal ization. Similar suggestions were repor-
al., 1988), horse mackerel and hake (Simeonidou et al.,
ted by Benjakul et al. (2005) after studding the effects of
1997), with blue whiting and light and dark muscles of
frozen storage on Ca2+-ATPaseactivity in actomyosins
hake (Aubourg, 1999; Aubourg et al., 1999), albacore
extracted from several tropical fish at -18°C for up to 6
tuna (Ben-Gigirery et al., 1999) and Nile perch
(Namulema et al., 1999). In most of these cases TBARS
Decrease in Ca2+-ATPaseactivities in mackerel and
reached a maximum and then fluctuated or decreased.
amberfish muscle was observed during storage at -10
TBARS is a measure of malondialdehyde, which is an
and -40°C for up to 6 months (Jiang et al., 1985). Ca2+-
end-product of lipid oxidation. The decrease of malon-
ATPase in Alaska Pol ock decreased during frozen sto-
dialdehyde in frozen stored fish muscle was attributed to
rage at -29 °C for 9 months (Scott et al., 1988). Ca2+-
interactions of malondialdehyde with amines, nucleo-
ATPase in myctophid species decreased during frozen
sides, nucleic acids, aminocontaining phospholipids, pro-
storage and the degree of decrease depended on the fish
teins or other by-products of lipid oxidation (Aubourg et
species (Seo et al., 1997). Ca2+-ATPase activities de-
creased in croaker, lizardfish, threadfish bream and
bigeye snapper during storage at -18°C for 24 weeks
Effects of storage time on expressible fluids
(Benjakul et al., 2003). Tejada et al. (2003) showed that
the Ca2+-ATPase activities decreased in the muscles of
Expressible fluids from stored frozen scal op meats
whole frozen stored gilthead seabream and hake after
showed a pronounced increase during the first 91 days of
one year at -20°C.
storage at -22°C. From that point until 301 days of sto-
The results of the present study with stored frozen scal-
rage, there were no significant changes in thawing and
lop meats are, therefore, in agreement with these other
total weight losses of frozen stored scal op meats (Figure
4). Several investigations have shown that the quantities
Storage Time (days)
Figure 4. The effect of the length of time of storage at -22?C on expressible fluids. Values are means ± SEM, n =
15. Groups with different letters (a, b, c) are significantly different (P<0.05). The ‘0’ storage time presents fresh
scal op meats
of exudates are influenced from the time a meat product
quent tissue-softening (Civera et al., 1996; Pan and Yeh,
is kept in the frozen state. This was the case with frozen
1993). Therefore, it is likely that the freezing process
stored turbot (Chevalier et al., 2001), round sardines
itself causes release of proteolytic enzymes from lyso-
(Suarez et al., 2002), whole and gutted seabream
somes of scal op meats with concomitant softening of
(Huidobro and Tejada, 2004) and Nile perch (Namulema
et al., 1999; Natseba et al., 2005).
From the results of the present study, there was no
Therefore the length of time of storage at -22°C affected
sign of a tendency for peak shear values of frozen scal op
the quantities of the exudates of frozen scal op meats.
meats to change in up to 301 days of storage at -22°C
Expressible fluids were related significantly with Ca2+-
(Figure 5). Similarly, it has been reported that shear
ATPase activities in actomyosin extracts from frozen
strength values from frozen stored gilthead seabream did
stored scal op meats (Table 1). This observation sug-
not change in up to 9 months of storage at -20°C (Pastor
gests that the water holding capacity of frozen stored
et al., 1999). Tissue toughening is common to many low-
scal op meats was possibly affected by the denaturation
fat fish species stored at subzero temperatures. This is
of myofibril ar proteins, as measured by the Ca2+-ATPase
the case with minced European hake (Careche and
activities in actomyosin extracts. Similar suggestions
Tejada, 1991), cod and haddock (Badi and Howel ,
were reported by Benjakul et al. (2003) for several tropi-
2002). The changes in the texture of fish muscle during
cal fish species.
frozen storage have been associated with the dena-
turation and aggregation of myofibril ar proteins, among
other causes (Haard, 1992; Mackie, 1993). The com-
Effects of storage time on instrumental texture
position of scal op meats is somewhat similar to white
flesh of less fatty fish (Webb et al., 1969). Moreover, the
results of the present study show a significant effect of
The peak shear forces obtained from the fresh scal op
storage time on denaturation of actomyosin extracted
meats were significantly higher than those of frozen and
from frozen stored scal op meats. Thus, scal op meats
immediately thawed scal op meats (Figure 5). This
were expected to toughen with time in frozen storage.
means that the freezing process itself caused softening of
However, factors related to tissue softening, e.g. release
raw scal op meats. Freezing and thawing cause lysis of
of proteases from lysosomes and cel disruption by ice
lysosomes and release into sarcoplasm of proteases,
crystals formation, may also exist in frozen and thawed
which cause breakdown of muscle proteins and cones-
seafoods and counteract the tissue-toughening factors
3900 Afr. J. Biotechnol.
Table 1. Pearson’s correlation coefficients between parameters of the stored frozen scal op meats.
HADH ble Fluids ATPase
*Significant at level 5%. ** Significant at level 1%. Numbers without asterisk are not significant; degree of freedom
= 5. Numbers in bold imply a strong relationship between the parameters.
Storage Time (days)
Figure 5. The effect of the length of time of storage at -22?C on peak shear forces. Values are means ± SEM, n =
15. Groups with different letters (a, b) are significantly different (P < 0.05). The ‘0’storage time presents fresh
scal op meats.
(Srinivasan et al., 1997).
slightly sour and rancid taste and slightly tough to tough
Thus, it is likely that factors which caused the two op-
and dry texture (ratings between 4 and 3; Table 2).
posing effects, i.e. tissue-softening and tissue-toughen-
The overal acceptability ratings of frozen scal op meats
ing, might both have been active in frozen stored scal op
stored at -22°C decreased significantly by 210 days
meats; because of their counteraction, individual effects
(Table 2), but the mean acceptability score was more
on textural changes in stored frozen scal op meats up to
than 3 (that is, ‘neither like or dislike’) after 301 days of
301 days at -22°C might have been diminished.
storage indicating that the scal op meats remained
acceptable at the end of the storage period. Changes in
flavour, texture and acceptance of stored frozen seafoods
Effects of storage time on sensory attributes
have been recorded by other workers. These changes
are mainly dependant on species, pre-freezing treatment
According to the ratings of the sensory panel, the fresh
and time and temperature of frozen storage. Thus,
scal op meats had a sweet to neutral taste and tender to
Simeonidou et al. (1997) found that the taste and texture
slightly tough texture (ratings between 5 and 4). The
of horse mackerel and Mediterranean hake were reduced
frozen scal op meats stored for 301 days had neutral to
during 360 days of storage at -18°C, but these attributes
Table 2. The effect of the length of time of storage at -22?C on sensory attributes
of scal op meats*.
Storage time (days)
4.6 ± 0.11 a
4.6 ± 0.14 a
4.2 ± 0.10 a
4.5 ± 0.15 a
4.6 ± 0.22 a
4.2 ± 0.20 a
4.8 ± 0.13 ab
4.6 ± 0.20 ab
4.4 ± 0.20 a
4.2 ± 0.20 ab
4.1± 0.17 ab
3.8 ± 0.20ab
4.17 ± 0.17 ab
4.0 ±0.19 ab
3.6 ± 0.30 ab
4.0 ± 0.25 ab
3.8 ±0.23 ab
3.3 ± 0.14 b
3.6 ± 0.15 b
3.5 ± 0.22 b
3.1 ± 0.20 b
*Means ± S.E.M, n = 15. Values in the same column with different letter (a, b) are
significantly different (P < 0.05). The ‘0’ storage time presents fresh scal op meats.
were stil at an acceptable level at the end of the storage
time of storage at -22°C affected the integrity of intra-
period. Namulema et al. (1999) showed that the texture,
cel ular (mitochondria) organel es, reduced the water
taste and overal acceptability of stored frozen Nile perch
holding capacity, caused denaturation of myosin (or
at -27°C for 10 weeks were similar to fresh fish. Yilmaz
‘actomyosin’) and affected the sensory attributes (flavour,
and Akpinar (2003) showed, also, that the frozen stored
texture and acceptability) of the frozen scal op meats.
fil ets of guitarfish at -18°C were acceptable after 6
Most of these changes in scal op meats were more pro-
months of storage. In addition, post-rigor scal op meats,
nounced after 91 days of storage at -22°C. It can, there-
frozen within 6 days after shucking, were acceptable after
fore, be concluded that although the frozen scal op meats
6 months at -30°C (Chung and Merritt, 1991a).
were in acceptable condition up to 301 days (that is, al-
The results of the present study are in agreement with
most 10 months), holding of these products for up to
these other studies and suggest that there was a loss in
three months (i.e. 91 days) at -22 °C may prevent the
flavour, texture and overal acceptability of stored frozen
negative changes in muscle structure, water holding
scal op muscles during 301 days storage at -22°C, but
capacity, myofibril ar proteins and sensory quality which
that these products were in acceptable condition at the
occur with longer storage.
end of the storage period.
Among the different indices checked, Ca2+-ATPase
activities in actomyosin extracts may be useful for asses-
sing the quality loss of the scal op meats stored frozen at
Correlations between parameters studied
-22°C, since a good linear correlation was obtained with
Ca2+-ATPase activities in actomyosin extracts from stored
time and scores of sensory attributes.
frozen scal op meats showed a significant correlation with
the storage time and sensory attributes, including texture
(Table 1). Significant correlations between parameters
related to changes in myofibril ar proteins and sensory
The author thanks al the staffs of the School of Life
texture are recorded in the literature for stored frozen fish
Sciences of The Robert Gordon University for their help
products. This is the case with stored frozen Patagonian
and corporation during the experimental work of this
hake at -20 and -30°C, (Ciarlo et al., 1985), stored frozen
study. The financial support from the Technological Edu-
fil ets and minces of hake at -18°C (Koning and Mol,
cational Institute of Messolonghi, Greek Ministry of Edu-
1991) and stored frozen minced sardines at -18°C
cation, is highly appreciated.
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satisfactory linear correlations with storage time and
sensory attributes may be useful methods for assessing
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