Journal of
Applied Ichthyology
J. Appl. Ichthyol. 28 (2012), 95–101
2011 Blackwell Verlag, Berlin
ISSN 0175–8659
Received: February 10, 2011
Accepted: July 27, 2011
doi: 10.1111/j.1439-0426.2011.01883.x
Differences in chemical, physical and sensory properties during shelf life assessment
of wild and farmed gilthead sea bream (Sparus aurata, L.)
By V. Šimat1, T. Bogdanović2, M. Krželj1, A. Soldo1 and J. Maršić-Lučić3
1
Center of Marine studies, University of Split, Split, Croatia; 2Regional Veterinary Laboratory, Split, Croatia; 3Institute of
Oceanography and Fisheries, Split, Croatia
Summary
The aim of this study was to determine and compare
differences in physical, chemical and sensory post-mortem
changes between wild (W) and farmed (F) gilthead sea bream
(Sparus aurata). Ungutted fish were stored in ice from
harvesting up to 20 days and freshness indicators were
analyzed at regular intervals. Proximate composition of the
samples differed in lipid (W = 0.86 ± 0.12; F = 4.18 ± 0.16)
and moisture content (W = 79.12 ± 0.48; F = 74.50 ±
0.82). Data from sensory evaluation were described using
linear regression models. Sensory schemes for cooked and raw
fish were found to be suitable in establishing specific attribute
deterioration and shelf life duration (W = 14 days;
F = 17 days). Changes in pH and dielectric properties were
influenced by differences in lipid content, while changes in total
volatile base nitrogen and trimethylamine showed high correlation with sensory assessment and storage time, but stayed
below the acceptance limit for human consumption
(W : 24.47 mg TVB-N ⁄ 100 g and 4.14 mg TMA-N ⁄ 100 g;
F : 26.18 mg TVB-N ⁄ 100 g and 3.84 mg TMA-N ⁄ 100 g),
and thus were not reliable indicators of quality changes during
storage in ice. Deterioration of flesh lipids, assessed by
thiobarbituric acid index, differed between the samples, but
presented no serious problem during storage time. In order to
determine the importance of individual results, all obtained
data were submitted to principal component analysis. Variations in sensory, physical and chemical assessment were
described by PC1 (storage time); variations in lipid and
moisture content were described by PC2 (capture grounds). A
clear separation of the investigated samples, according to the
storage time and capture grounds, was observed.
Introduction
Freshness and spoilage are the most important criteria to
determine the overall quality of food products. Considerable
effort has been invested in the search for suitable methods to
assess freshness while the product is still edible by setting
quantitative standards on spoilage processes (Sykes et al.,
2009). Factors such as feed access and composition, as well as
environmental history differences, affect sensory attributes and
quality of wild and farmed fish. As one of the main species
farmed in Mediterranean countries, the demand for fresh
gilthead sea bream has increased significantly over the past
decade; the investigation of quality changes during storage
continues to be of major interest to industries, retailers and
consumers; however, most studies have been conducted on
farmed sea bream (Alasalvar et al., 2001; Cakli et al., 2007;
U.S. Copyright Clearance Centre Code Statement:
Özogul et al., 2007). Although limited, the literature indicates
significant differences in organoleptic characteristics of wild
and farmed samples of the same species. Farmed specimens
have a softer texture and less robust flavour, thus consumers
prefer farmed fish from the wild (Alasalvar et al., 2002;
Grigorakis et al., 2003). Of interest is to compare other quality
indicators, such as volatile amines, dielectric properties or
deterioration of flesh lipids during ice storage.
Sensory evaluation is the most commonly used method for
quality assessment of raw fish; the Quality Index Method
(QIM) has been suggested as being a precise, objective, nondestructive, rapid, simple to apply and species-specific sensory
method for an independent description of outer appearance
attributes of raw fish using a scoring system of 0–3 demerit
index points for each characteristic (Ólafsdóttir et al., 1997;
Huidobro et al., 2000; Martinsdóttir et al., 2009). The total
sum of all points gives an overall sensory score, a so-called
quality index (QI). Freshness parameters such as texture,
odour and flavour are used in the Torry freshness scoring to
determine the sensory response of cooked fish samples (Martinsdóttir et al., 2001). Post-mortem quality changes in fish
vary with season, species, fishing method, handling, and
holding temperature; therefore physical and chemical muscle
changes should be correlated with sensory assessment results
(Huss, 1988; Sikorski et al., 1990; Ólafsdóttir et al., 1997). The
post-mortem muscle content of volatile amines provides
information on the progression of spoilage and is suitable
for confirming sensory data (Venugopal, 2002), while changes
in dielectric properties of fish skin are closely related to
spoilage rates.
The objective of this study was to identify specific postmortem changes and shelf life oftwo fisheries products of the
same commercially important species: wild and farmed
gilthead sea bream. To achieve this we determined and
compared their physical, chemical and sensory changes while
preserving the fish on ice.
Materials and methods
Sampling of the fish and storage conditions
A total of 400 commercial-sized fish (380–420 g) were used in
the study: 200 farmed gilthead sea bream (Sparus aurata) were
obtained directly from the local farm (F) and 200 fish were
caught by fishermen in the coastal part of the Central Adriatic
(W). Samples were taken in April 2010. Fish were killed by
immersion in ice-cold water and placed in self-draining
polystyrene boxes, packed in flaked ice and delivered to the
laboratory within 3–4 h of harvesting. Temperature of the fish
0175–8659/2012/2801–0095$15.00/0
96
upon arrival was 2 ± 1C. First samples for chemical and
sensory analysis were taken on the same day, while the
remainder of the fish were repacked for 20 days in cold storage
at 0 ± 2C. Fresh ice was added daily in a 2 : 1 fish-to-ice
ratio. To avoid direct contact of ice with the fish skin, very thin
plastic sheeting was used to cover the fish.
Proximate composition analysis
Proximate composition analyses of wild and farmed gilthead
sea bream were conducted upon arrival of the fish (day 0).
Randomly chosen fish (four wild and four farmed) were filleted
(with skin on) and homogenized in a cutting mill (GM 200;
GRINDOMIX, Retsch, Germany). The homogenates were
used for all chemical analyses. Moisture, protein, total lipid
and ash content were determined according to AOAC (2000)
procedures. All analyses were done in triplicate for each fish.
V. Šimat et al.
Table 1
Quality Index Method scheme used for sensory assessment of wild and
farmed sea bream samples (according to Huidobro et al., 2000)
Parameters
Appearance
Skin
Slime
Flesh
Firmness
Physical and chemical analysis
The pH value, thiobarbituric acid index, and volatile amines
(TVB-N and TMA-N) of both wild and farmed samples were
investigated on days 0, 7 and 15 of ice storage. The pH was
measured using a digital pH meter (Iskra pH-Meter MA 5705,
Slovenia) equipped with a glass electrode, calibrated at four
and seven. The electrode was dipped into the fish and distilled
water (1 : 1) mixture at ambient temperature (Kyrana and
Lougovious, 2002).
Changes in the dielectric properties of both wild and farmed
samples were determined using the GR Torrymeter (Distell
Industries Ltd., Scotland, UK) over 20 days. A single measurement was obtained from each of the 16 (eight wild and
Demerit points
Very bright
Bright
Blurred, faded
Clear-transparent
Slightly cloudy ⁄ cloudy
0
1
2
0
1
Elastic
Marked by pressure
0
1
Fresh
Neutral
Strongly fishy
Off odours
0
1
2
3
Clear-translucent
Slightly opaque
Opaque ⁄ bloody
Convex
Flat
Concave
0
1
2
0
1
2
Bright ⁄ dark red
Brownish red ⁄ discoloured
Fresh ⁄ seaweed
Neutral
Fishy
Off odours
0
1
0
1
2
3
0–15
Odour
Eyes
Colour
Sensory evaluation of cooked and raw fish
During the shelf life study, six trained and experienced sensory
panel members made sensory evaluations of the cooked fillets
and raw fish. Maximum storage shelf life of wild and farmed
gilthead sea bream was determined by sensory evaluation of 16
(eight wild and eight farmed) cooked samples, using a Torry
scheme adapted to raw gilthead sea bream using a descriptive
scale from 10 to £3, with 10 being absolutely fresh fish and £ 3
being completely putrid or spoiled fish (Alasalvar et al., 2001).
The dorsal halves of the fish fillets were placed in a plastic bag
with water added, then sealed and heated in a microwave oven
(600 W) for 3 min. After 5 min the fillets were served to
panelists and assessed for odour, flavour and texture. An
average score £5.5 was used as the sensory rejection point
(Lougovois et al., 2003; Gonçalves et al., 2007).
Raw fish were evaluated using the Quality Index Method
(QIM) for gilthead sea bream earlier described by Huidobro
et al. (2000). The QIM scheme consists of eight parameters,
using a total of 15 demerit points (Table 1). Each panelist
assessed 16 (eight wild and eight farmed) whole fish from day 0
until spoiled. A score of 0–3 demerit points was given for every
change in evaluated parameter (0 representing the highest level
of freshness). The panelists were requested to evaluate and
score quality on evaluation sheets by feeling, smelling and
examining the samples, describing whether there were differences between samples, commenting on sample characteristics,
and rating intensity of specific sensory attributes (Table 1).
The panel evaluated both cooked and raw samples, coded with
random three-digit numbers on days 0, 3, 5, 8, 11, 14 and 17 of
storage.
Attributes
Shape
Gills
Colour
Odour
Quality index (QI)
eight farmed) fish by applying the meter probe above and
parallel to the lateral line, just behind the gill cover. Instrument
readings were read on a digital display, with 17 being the
highest value and zero the lowest.
Thiobarbituric acid index (TBA) was determined in
trichloracetic acid-fish extracts as previously described by
Vyncke (1970) and Lemon (1975), using a spectrophotometer
(PRIM Advanced, Secomam, France). Results were expressed
as mg malondialdehyde ⁄ kg muscle (mg MA per kg).
Total volatile base nitrogen (TVB-N) and trimethylamine
nitrogen (TMA-N) content of wild and farmed gilthead sea
bream samples were determined by direct distillation of fish
extracts as previously described in Šimat et al. (2009a) and
expressed as mg TVB-N ⁄ TMA-N ⁄ 100 g fish muscle (mg per
100g).
Statistical analyses
Results of repeated analyses were reported as average ± standard deviation. Differences between wild and farmed samples
were analysed statistically by StudentÕs t-test. For comparison
of means, one-way analysis of variance (ANOVA) followed by
FisherÕs least significant difference (LSD) test at the 95%
confidence level was used. Data from sensory evaluation
(cooked and raw fish) and Torrymeter measurements were
described using linear regression models and the equations for
regression lines calculated from all individual data. PearsonÕs
correlation coefficients were used to determine the relation
between the physical and chemical measurements to sensory
panel results. The principal component analysis (PCA) was
used to determine the importance of individual parameters and
the relationship among them. Prior to PCA the variables were
standardized to a mean of zero and variance of one. All
Shelf life parameters of wild and farmed gilthead sea bream
97
Table 2
Proximate analysis (means ± standard deviation; n = 12; % on wet
weight basis), wild and farmed gilthead sea bream
Sample
Moisture (%)
Protein (%)
Lipid (%)
Ash (%)
Wild
79.12 ± 0.48a 19.87 ± 0.36a 0.86 ± 0.12a 1.12 ± 0.06a
Farmed 74.50 ± 0.82b 19.55 ± 0.30a 4.18 ± 0.16b 1.05 ± 0.03a
a–b
Means in the same column and with same letter do not differ
significantly, P < 0.05.
statistical analyses were performed using the Statistica 8
(StatSoft Inc., Tulsa, OK, USA) software package.
Results
Proximate analysis of wild and farmed gilthead sea bream
Proximate composition analyses of wild and farmed gilthead
sea bream are shown in Table 2. As expected, significantly
higher lipid content and correspondingly lower moisture
content were found in farmed samples. A statistically significant difference was observed between the means of moisture
and lipid content, but not between crude protein and ash
content of wild and farmed gilthead sea bream. Additional
lipid analyses, taken on days 7 and 15 of ice storage, showed
no significant differences in lipid content at the different stages
of storage. Average lipid content during the entire storage time
was 0.92 ± 0.14% for wild and 4.29 ± 0.16% for farmed
samples.
Sensory assessment
Results from the sensory evaluation of cooked fillets from raw
wild and farmed gilthead sea bream are shown in Fig. 1.
Sensory quality of both wild and farmed fish decreased with
storage time. A statistically significant difference (P < 0.05)
was observed between the means of Torry scores (odour,
flavour and texture) of wild and farmed fish. Wild samples
received lower scores throughout the storage, especially after
day 11 when boiled dish cloth odour, intensive sour offflavour, flakiness of the fillet and dry and fibrous texture
developed. After 14 days in ice the farmed samples were
characterized by a boiled potato or cheesy ⁄ sour milk odour,
Fig. 2. Changes in QI scores, wild and farmed gilthead sea bream
samples against storage time on ice. Each point = mean of eight fish;
vertical bars = standard deviation
slightly off umami-like flavour and a rubber but fibrous
texture. Colour was not taken into the calculation of the Torry
score, but panelists were asked to observe and comment on the
colour of cooked fillets. Five panelists found the greyish colour
of wild samples fillets less appealing. The higher lipid content
did not seem to contribute significantly to the development of
rancidity. Only two panelists reported a slightly rancid flavour
in cooked farmed fish samples at the end of storage. Shelf lives
of farmed and wild samples were calculated from the regression line equations, taking a score of 5.5 as the rejection point,
and were found to be 17 and 14 days, respectively (Fig. 1).
Sensory attributes were described by means of the quality
index score (QI) over storage time on ice (Fig. 2). QI score
increases evolved linearly, showing high positive correlation
with storage time for both wild (r = 0.989, P < 0.01) and
farmed (r = 0.968, P < 0.01) samples. Farmed samples
received lower QI scores throughout storage. Main differences
between the two fish groups were in skin appearance, flesh
firmness, odour and gill colour. During storage of farmed
samples the general fading of colours, with yellowish slime on
the skin, slow loss of flesh firmness and evolution of milky
mucus on gills were observed. In wild fish a blurred greyish
colour, rapid loss of firmness and scales, and brown-clotted
mucus on the gills developed with increased storage time.
Maximum QI score was reached on day 14 for wild and day 17
for farmed samples. These results suggest that the QIM scheme
was suitable for freshness assessment of both wild and farmed
raw gilthead sea bream stored on ice.
Physical and chemical analysis
Fig. 1. Changes in cooked sensory scores (Torry score), wild and
farmed gilthead sea bream samples against storage time on ice. Each
point = mean of eight fish; vertical bars = standard deviation
Levels of pH, TBA (mg MA per kg), TVB-N (mg per 100 g)
and TMA-N (mg per 100 g) at three different stages of ice
storage for wild and farmed gilthead sea bream are shown in
Table 3. First pH measurements of the samples were taken 6 h
after death, thus low initial pH could be a result of muscle
glycogen being metabolized into lactic acid. The pH of the
muscle increased during storage in both wild and farmed
samples. Fish were similar in size thus the statistically
significant difference (P < 0.05) observed between the samples
could result from different feed (not analysed in the study) or
harvesting methods. At the end of storage the pH values of
both groups grew to levels that indicate the production of
some alkaline metabolites correlated with spoilage.
98
V. Šimat et al.
Table 3
Changes in muscle pH, thiobarbituric acid index (TBA) and volatile
amines (TVB-N and TMA-N), wild and farmed gilthead sea bream at
three stages of ice storage (means ± standard deviation; n = 12)
Measured parameters
pH
Fish samples
Storage
time (days) Wild
0
7
15
TBA (mg MA per kg)
0
7
15
TVB-N (mg per 100 g)
0
7
15
TMA-N (mg per 100 g) 0
7
15
6.02
6.14
6.71
0.24
0.31
0.84
17.23
19.26
24.47
0.62
1.97
4.14
±
±
±
±
±
±
±
±
±
±
±
±
Farmed
0.03a 6.15 ± 0.02a
0.02b 6.10 ± 0.02b
0.02c
6.37 ± 0.03c
0.09a 0.28 ± 0.22a
0.12a 0.79 ± 0.28b
0.12b 0.93 ± 0.22b
0.36a 18.14 ± 0.38a
0.32b 20.93 ± 0.24b
0.42c 26.18 ± 0.28c
0.16a 0.81 ± 0.18a
0.12b 0.97 ± 0.14a
0.12c
3.84 ± 0.18b
a–c
Means of each parameter in same row column with same letter do
not differ significantly; P < 0.05.
Changes in dielectric properties between wild and farmed
gilthead sea bream showed statistically significant differences
(P < 0.05) during storage (Fig. 3). Due to their higher lipid
content, farmed samples showed faster decline in Torrymeter
readings throughout the storage and a higher variability
between individual readings, especially after day 11 of storage.
Values determined at the end of shelf life of wild and farmed
fish samples (days 14 and 17) were around 10 and 6; according
to manufacturers these values would indicated perfectly fresh
and good quality fish. High negative correlation coefficients
were found between Torrymeter readings and QI scores for
both wild (r = )0.979, P < 0.05) and farmed (r = )0.993,
P < 0.05) samples; however, the values of dielectric properties
during shelf life suggested that the range of Torrymeter
readings were different between wild and farmed gilthead sea
bream stored in ice. Over the first 3 days farmed samples
showed readings higher than those suggested by the manufacturer (>16), thus the measuring scales should be set differently. Values ‡12 (wild) or ‡13 (farmed) would indicate very
fresh fish (4–5 days on ice), while the values <9 (wild) or <6
(farmed) would indicate fish unfit for human consumption.
The initial values of TBA were low for both wild and farmed
samples (Table 3). The t-test showed no statistically significant
difference (P > 0.05) between the means of TBA in the fresh
muscles, however, the increase over time was found to be
significant, thus the difference between wild and farmed fish at
the end of the storage. On day 14 of sensory analysis two
panellists reported slight rancidity in flavour of cooked farmed
fish samples, therefore additional analysis of TBA were done
on days 16 and 17 of the ice storage. Corresponding values of
TBA on those days were 0.89 ± 0.24 and 1.12 ± 0.18 mg MA
per kg. Higher correlation coefficients were observed between
TBA and sensory scores (QI and Torry scores) of farmed
(r > 0.974) than of wild samples (r > 0.747).
Levels around 18 mg TVB-N per 100 g were found at the
beginning of storage in both wild and farmed gilthead sea
bream samples (Table 3). The increase of TVB-N levels with
storage time was small, <10 mg per 100 g over 15 days.
Despite the initial levels close to the limit established for
freshly caught fish (20 mg per 100 g), values at the end of
storage remained below the recommended limit for acceptability of 30–35 mg TVB-N ⁄ 100 g. Similar results were
obtained for TMA-N analysis (Table 3), and levels found
after 15 days of storage were <5 mg per 100 g. At the sensory
rejection point of the samples (F = 17 days, W = 14 days),
the content of volatile amines did not indicate spoiled fish, thus
these should not be taken as reliable indicators of freshness for
wild and farmed gilthead sea bream.
The qualitative characteristics of studied parameters
described by PCA are shown in Fig 4. Distinct separation of
wild and farmed samples was observed, placing the two sets of
data opposite to each other and separating them according to
the storage time and catching grounds (Fig. 4a). The proportion of variance accounted for by the first two principal
components (PC1 and PC2) was 93.32%, while the remaining
PCs each accounted for less than 3% of the total variance.
High correlations were observed among all parameters studied. The most important parameters were quality index (0.941)
and Torry scores (0.966), while the remainder of the studied
parameters showed correlations >0.877 (Fig. 4b). Parameters
with the highest variable contributions (between 0.13 and 0.16)
to PC1 were storage time, sensory assessment (QI and Torry
score), TVB-N content, TBA and pH value. The lipid content
of the fish had the highest contribution (0.74) to PC2.
Discussion
Fig. 3. Changes in Torrymeter readings against storage time on ice,
whole gilthead sea bream samples (wild and farmed). Each point =
mean of eight fish; vertical bars = standard deviation
The chemical composition varies greatly between species and
individuals of the same species, mostly due to age, sex,
migration, environment and seasonal variations (Hyldig et al.,
2007), but also due to feed composition and activity of the fish
(Alasalvar et al., 2002). Using the 5% total lipid level as a cutoff point between low and medium fat fish (Ashton, 2002), the
muscle lipid content defines both fish groups analysed in this
study as low fat fish.Total body lipids are known to increase
with size, and in all cases wild fish were found to have much
lower lipid content than their farmed counterparts (Grigorakis
et al., 2002). The protein content is considered a stable
component in fish proximate composition, with some changes
related to fish weight. Fish analysed in this study had similar
weights, thus the protein and ash content of the samples did
not differ significantly. Previous studies also reported similar
proximate composition of wild and farmed gilthead sea bream
(Kyrana et al., 1997; Alasalvar et al., 2002; Grigorakis et al.,
2003).
Shelf life parameters of wild and farmed gilthead sea bream
(a)
(b)
Fig. 4. Score plot (a) and correlation loading plot (b) from PCA
describing quality index score (QI), Torry score (Torry), Torrymeter
measurements (TM), pH value (pH), thiobarbituric acid index (TBA),
lipid content (FAT), moisture content (MOIST), TVB-N and TMA-N
content, wild (W) and farmed (F) gilthead sea bream samples during
different storage times (ST) in days on ice (0–17)
Differences in sensory assessment of farmed and wild
gilthead sea bream were observed in both the cooked and
raw sensory scores. The evolution of spoilage given as the sum
of demerit points was more pronounced in wild samples.
Farmed fish had a less intensively fishy taste, but were milkier
and whiter in appearance, which could be related to higher
lipid content; the texture was also firmer compared to the wild
fish, which could be related to lower water content. Grigorakis
et al. (2003) found wild gilthead sea bream to have greater
acceptance than farmed fish and that this preference seemed to
be related to taste and flavour of the fish rather than to textural
properties; however, they found much higher lipid contentscompared to samples analysed in our study. Alasalvar et al.
(2002) found no difference over time between sensory scores of
cooked farmed and wild sea bream. These differences can be
explained by the fact that cooking the fish may mask or
remove undesirable changes observed, providing these changes
are not extreme.With firmer texture and milder odours and
99
lower demerit points of eight quality parameters, the farmed
fish in our study resulted in better acceptance and longer shelflife compared to wild samples. The storage life of farmed
gilthead sea bream determined in other studies was similar to
our results and ranged between 9–20 days depending on the
packing method (Kyrana et al., 1997; Huidobro et al., 2000;
Alasalvar et al., 2001; Lougovois et al., 2003; Chouliara et al.,
2004; Özogul et al., 2007). The maximum shelf life of wild
gilthead sea bream determined by sensory evaluation was not
previously reported in the literature; however, Alasalvar et al.
(2002) found the limit of acceptability of wild gilthead sea
bream to be 16–18 days based on concentration of ATP
breakdown compounds during ice storage.
Typical pH of the live fish is around seven, thus the initial
low pH of the samples could reflect good quality and freshness
of the fish or that fish underwent some stress before capture
(Kristoffersen et al., 2006). Tejada and Huidobro (2002)
reported rapid decrease from 7.2 to 6.4 in the initial pH of
gilthead sea bream muscle in the first 5 h after death, and the
increase in muscle pH to 6.8 during storage regardless of the
slaughter method. In a shelf-life study of ice stored gilthead sea
bream Kyrana et al. (1997) recorded low initial pH (6.10–6.20)
in the muscle. After 1 week the pH began to increase to the
final value of 6.60.
Although some failures had been reported for the Torrymeter application in the shelf life study (Kent and Oehlenschläger, 2009), the Torrymeter was found to be a suitable
instrument for freshness assessment of whole fish in the
present and in various studies over the years (Pivarnik et al.,
1990; Sakaguchi and Koike, 2002; Lougovois et al., 2003;
Oehlenschläger, 2003; Šimat et al., 2009b). The operational
ÔvalueÕ range of the Torrymeter is governed by the dielectric
range of the fish and may be used to indicate the spoilage
process and remaining shelf-life in whole fresh fish (Vaz-Pires
et al., 1995). Each fish species would have a different range of
dielectric properties. Lougovois et al. (2003) suggested that
values ‡than 11 would indicate very fresh farmed gilthead sea
bream fish (4 days on ice) and that a value of six would be
marginal; however, the lipid content, which could explain the
differences between the data, was not reported in the Lougovois et al. (2003) paper.
The values of TBA did not reach the quantity generally
considered the limit of acceptability for fish (5–8 mg MA per
kg) (Nuñes et al., 1992) and were in range of the previously
reported TBA levels of farmed Sparidae species 0.37–
1.42 mg MA per kg (Tejada and Huidobro, 2002; Cakli et al.,
2007; Abbas et al., 2008). The difference in rancidity between
wild and farmed sea bream was expected, due to the difference
in lipid content; however, oxidation spoilage did not occur in
either wild or farmed samples during storage.
Fresh fish contain 5–20 mg TVB-N ⁄ 100 g and 2–4 mg
TMA-N ⁄ 100 g (Shakila et al., 2003) while levels of 30–35 mg
TVB-N ⁄ 100 g and 5–10 mg TMA-N ⁄ 100 g are considered
the limit of acceptability for most marine fish species
(Ababouch et al., 1991; Connel, 1995). Higher initial concentrations of TVB-N could be a result of high levels of nonprotein nitrogen previously reported in the flesh of gilthead sea
bream (Kyrana et al., 1997). Most studies reported the
increase of TVB-N with storage time, regardless of storage
conditions and the later increase in volatile amines in Sparidae
species over the limit of acceptance after 20 days of storage in
ice (Kyrana et al., 1997; Tejada and Huidobro, 2002; Cakli
et al., 2007; Özogul et al., 2007). Some authors suggested that
existing regulations should be adopted in the way the gilthead
100
sea bream is included in the group of fish for which the TVB-N
level of acceptance for human consumption is set at 25 mg per
100 g (Kyrana et al., 1997; Tejada and Huidobro, 2002;
Grigorakis et al., 2003; Özogul et al., 2007). TMA-N comes
from the reduction of trimethylamine oxide (TMAO) by
bacterial activity (Dalgaard, 2003), and levels found in the
aerobically stored fresh fish rejected by the sensory panel vary
between 10 and 15 mg per 100 g (Dalgaard et al., 1993). The
low concentrations and slow increase of TMA-N observed in
our study could be explained by low TMAO concentrations
found in gilthead sea bream (Kyrana et al., 1997). Low
increase of TMA-N with storage was observed in other
Sparidae species, 1.8–4.3 mg TMA-N ⁄ 100 g was found at
sensory rejection points (Kyrana et al., 1997; Kilinc et al.,
2007). Low levels of volatile amines at the end of shelf life did
not reflect the spoilage evolution over storage time. The
differences observed between farmed and wild samples could
be related to feed differences or to initial microbial flora;
however, these were not studied to support such a thesis.
PCA of sea bream samples was performed on mean values
of nine quality parameters to identify their similarities and
differences, plus identification of the most effective variables
(sensory assessment, lipid content) and noting the relationship
among the variables themselves. This affirms the use of QIM
and Torry schemes as necessary in describing different freshness levels of gilthead sea bream in shelf-life studies. The PCA
analysis was found very useful in determining importance of
the individual parameters, clearly separating the investigated
samples according to storage time and capture grounds.
In conclusion, most differences in the two fishery products of
the same species could be related to lipid content, and thus the
feed intake and reduced activity of the farmed samples. All
studied parameters showed high correlation with sensory
assessment and storage time, and thus are good indicators of
changes in quality during storage in ice. However, the late
response of TVB-N and TMA-N in post-mortem muscle
makes them less useful as indicators by themselves. Fishery
products from gilthead sea bream are widely marketed, thus
the differences in physical, chemical and sensory post-mortem
changes between wild and farmed samples should be taken
into consideration during marketing and production.
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AuthorÕs address: V. Šimat, Center of Marine studies, University of
Split, Livanjska 5 ⁄ III, 21000 Split, Croatia.
E-mail: [email protected]