Eur Food Res Technol (2006) 222: 41–47
DOI 10.1007/s00217-005-0078-y
ORIGINAL PAPER
Réda Triqui
Sensory and flavor profiles as a means of assessing freshness
of hake (Merluccius merluccius) during ice storage
Received: 28 April 2005 / Revised: 8 June 2005 / Accepted: 10 June 2005 / Published online: 27 August 2005
C Springer-Verlag 2005
Abstract Freshness of hake stored in ice was evaluated
by sensory and instrumental means. The European Union
scheme and the quality index method (QIM) were used to
sensorially index freshness. Aroma extract dilution analysis (AEDA) and SPME-headspace determinations were
applied to monitor important odorants of hake at different freshness stages. Based on AEDA, potent odorants of
hake in the very fresh state were (Z)-1,5-octadien-3-one
and 3 unknown volatiles. Attempts were made to relate
overall odor changes to individual volatiles: after 2 days
storage, the higher FD-factors found for trans-4,5-epoxy(E)-2-decenal, (Z)-4-heptenal, methional, and 2-acetyl-1pyrroline were associated with the “masking” of the seaweed character, whereas the higher concentrations of (Z)1,5-octadien-3-one and (Z)-4-heptenal in hake that reached
the B grade were likely responsible for the pungent odor.
No highly volatile odorants were detected in hake using
SPME-headspace analysis, but in contrast to AEDA, the
odor intensity of some volatiles, e.g., (E,Z)-2,6-nonadienal
and 3-methylnonane-2,4-dione indicated a higher contribution. The detection of two low boiling odorants associated
with fresh fish flavor is reported for the first time.
Keywords Hake . Merluccius merluccius . Freshness .
Sensory . AEDA . SPME headspace
Introduction
Hake is a member of the Merlucciidae family, a sister of
the closely related cod family (Gadidae). Merluccius merluccius is the only hake species occurring in European
waters. It is a lean fish with a fat content well below 1%.
In Morocco, and in many Mediterranean countries includR. Triqui ()
Hidaoa department, Institut Agronomique et Vétérinaire Hassan
II, Rabat-Instituts, Madinat Al Irfane,
B.P 6202,, 10101 Rabat, Moroccco
e-mail: [email protected]
Tel.: +212-(0)-37-77-17-58/59/45
Fax: +212-(0)-37-77-81-35
ing Spain and Portugal, hake is among the most popular
marine species and is usually sold fresh on ice. It is only a
few years ago since it began to be popular among northern
Europe consumers, as a result of new convenience frozen
products, including IQF fillets and slices, breaded fillets,
and fish fingers [1].
Freshness makes a major contribution to the quality of
fish and fishery products. In Europe, the most commonly
used method for quality assessment of raw fish in the inspection service and fishing industry is the EU-scheme.
The alternative objective quality index method (QIM) for
raw fish is increasingly being adopted. The QIM methods
are described in a model that is used to predict the keeping
qualities of fish [2]. Within a concept of fresh fish market
strategy initiated in the Netherlands and Belgium, QIM was
aimed to select fish for the quality label at the auction with
a maximum storage time not more than 2 days in ice [2].
Sensory analysis has been considered to be less objective and reproducible than instrumental analysis, due to the
use of humans. The need to develop methods for a reliable
determination of freshness in fish has been emphasized,
especially with respect to differentiating the early freshness stages. Classical chemical methods for assessing the
freshness of fish are the determination of both total volatile
basic nitrogen (TVB-N) and trimethylamine (TMA-N). Rejection limits of 40 and 12 mg per 100 g have been set
for TVB-N (Directive95/149/EEC) and TMA-N (Directive
91/493/EEC), respectively [3].
In search for suitable chemical indices to grade the freshness of ice-stored Mediterranean hake (Merluccius merluccius), Baixas-Nogueras et al [4] used flow injection/gas
diffusion (FIGD) methods for (TMA-N) and (TVB-N) determinations. They found the P ratio criterion (percentage
quotient between TMA-N and TVB-N) to be more suitable
as an indicator of the degree of freshness than individual
TMA-N or TVB-N values. P ratio changed more strongly
during the early storage period, when the concept of freshness is most relevant. Production of biogenic amines in
gutted hake stored in ice for 25 days has been also studied for potential use as quality indices [5]. Increases in
the levels of cadaverine and agmatine were observed from
42
day 5 of storage and were significantly different on day 12.
Both amines could be used as indices for freshness of hake
since they would provide information about the changes
occurring in hake muscle in the early stages of storage. In
a study by Medina et al [6], capillary zone electrophoresis
(CZE) profiles of methanol-soluble compounds extracted
from white muscle of fatty and lean fish species, including
hake (Merluccius merluccius), were used to assess freshness during chilling. Intensity of peaks with short retention times decreased during chilling storage, while that of
longer retention time increased. On the basis of statistical
correlation analysis with time of chilling and sensory measurements, the authors found the method to be sensitive
enough to detect loss of quality from the start of chilling as compared to other well-established methods such as
TVB-N.
Few studies focused on correlating sensory and chemical
attributes of hake during ice-storage. Changes in pH, TMAN, and TVB-N were studied in whole gutted hake stored
in ice [7]. The above parameters were found to be more
suitable as indices for spoilage of hake along with sensory
assessment (inspection and test panel).
Odor is one of the most important parameters used to
evaluate fish freshness. Measurements of characteristic
volatile compounds can be used to monitor the freshness
or spoilage state of fish [8]. Despite a sizeable amount
of evidence for lipoxygenase-formed compounds as imparting fresh fish odor, our understanding of the contribution of many identified odorants to seafood flavor remains
limited. In addition, either extracts or headspace samples
have been analyzed, thereby neglecting the impact of the
highly volatile or low volatile compounds, respectively
[9]. Grosch and coworkers have applied GC-olfactometry
methods: Aroma extract dilution analysis (AEDA) and gas
chromatography/Olfactometry of static headspace samples
(GCO-H) to determine the sensory most important compounds in several foods including trout, salmon and cod
[9–12].
To the best of our knowledge, no reports on fresh hake
flavor could be found in literature. The present study examines the sensory and flavor profiles of hake (Merluccius
merluccius) during ice storage. Freshness grading of fish
was carried out sensorially using the EU freshness grading
scheme for white fish [13] and the QIM [2]. Screening of the
potent odorants of hake at three different ice storage stages
was performed using the method of Aroma extract dilution
analysis (AEDA) [14]. Attempts were made to compare
overall sensory changes to individual potent volatiles. In
a separate ice storage trial, changes in the volatile profiles
of hake at different freshness stages were analyzed by the
method of SPME headspace.
Materials and methods
Chemicals
Trimethylamine-HCl (TMA) was from Sigma. Pure samples of (Z)-4-heptenal, methional, 2-acetyl-1-pyrroline,
(E,Z)-2,6-nonadienal, 3-methylnonane-2,4-dione and
(E,E)-2,4-decadienal were gifts from Prof. Dr. Peter
Schieberle (Deutsche Forschungsanstalt für Lebensmittelchemie, Garching, Germany). The remaining compounds
were previously identified [15].
Storage trial for AEDA
Fresh hake of the species M. merluccius (10 kg; around
4–5 h after catching) were obtained in a wholesale fish
market just after landing. Hake were caught off the coasts
of Mehdia (northern central Moroccan Atlantic coast) in
March (average temperature = 20 ◦ C). The mean length and
weight of fish were 23 ± 2 cm and 95 ± 2 g, respectively.
Fish were immediately transported to our laboratory in
crushed ice. In the laboratory, the fish were placed in a selfdraining polystyrene box with crushed ice (fish-to-ice ratio
2:1), replenishing melted ice daily. The box was stored in
a refrigerator at 4 ◦ C. Samples (three fish) were taken on a
daily basis, up to 11 days of storage for sensory evaluation.
Fish temperature was measured immediately after sampling
by placing a thermometer in the fish anal orifice. AEDA
was carried out on three samples taken (1) just upon arrival
of fish to the laboratory (S1), (2) after 48 h storage (S2),
and (3) on the seventh day of storage (S3).
Storage trial for SPME analysis
Fresh hake (10 kg; around 4 to 5 h after catching) caught
off the northern central Moroccan Atlantic coast in April
(average temperature 22 ◦ C) were obtained from the same
wholesale fish market just after landing. The mean length
and weight of fish were 25±2 cm and 106±2 g. Fish were
then transported and stored as described for the AEDA
trial. Sampling was carried out daily, up to fitness for consumption. Before SPME analysis were begun, specimens
of samples were taken for sensory evaluation.
Sensory evaluation
For both storage trials, fish were inspected at each time of
sampling by two panelists familiar with the fish inspection
methods used in this study. The freshness state of hake was
assessed both by the EU scheme for white fish and by the
QIM. There are three levels in the EU scheme, E (extra),
A, B, where E is the highest quality and below B (or grade
C) is the level where fish is discarded for human consumption. The EU scheme is not taking in account differences
between species. QIM is based on significant sensory parameters for whole fish using many weighted parameters
and a score system from 0 to 4 demerit points. Scores are
added to give an overall sensory score, the so-colled quality index. QIM gives scores of 0 to very fresh fish and
an increasingly larger total result as the fish deteriorates.
No single parameter can unduly imbalance the score [2].
We used the scheme developed for hake (M. merluccius)
43
Table 1
Quality index method (QIM) scheme for hake (M. merluccius)
General appearance
Parameter
Characteristic
Demerit points
Surface
Grey, bright
Grey, less bright
Grey (pink shade in dorsal region)
Grey (pink-yellow shade in dorsal region)
Firm, elastic
Firm, less elastic
Less firm, much less elastic
Soft
Transparent, bright
Slightly opalescent
Opalescent
Opalescent, bloodstained
Black, bright
Black grayish
Black grayish (typical of cataract)
Grey, whitish
Plane
Slightly sunken
Sunken
Dark red or bright red, little translucent mucus
Dark red or intense red, slightly opalescent mucus
Dark red, dense opalescent mucus
Discolored red, yellow-brownish mucus
Fresh, sea weedy
Fresh, Less intense sea weedy
Neutral
Slightly acid or pungent, fruity
Acid or pungent or bitter or rancid
Total
0
1
2
3
0
1
2
3
0
1
2
3
0
1
2
3
0
1
2
0
1
2
3
0
1
2
3
4
0–21
Flesh firmness
(dorsal region)
Eyes
Clarity (cornea)
Pupil
Shape
Gills
Color
Odor
at the “Institute of Seafood Quality Investigations” (IPIMAR), Portugal [16] (Table 1). While in this scheme odor
description is limited to the gills, we added separate skin
odor descriptors for the purpose of this study that were not
included in calculating total demerit points.
Isolation of the volatiles for AEDA
Fish (three specimens made 200 g) were manually beheaded, gutted, and filleted. The fillets were immediately cut in small pieces, soaked in methylene chloride
(150 ml), and then homogenized using an Ultra-turrax
for 3 min. Further preparation steps were as recently described [17]. Hake volatiles were recovered using the modified [15] vacuum distillation method described by Sen
et al. [18]
Capillary gas chromatography (AEDA)
High-resolution gas chromatography (HRGC) was performed by means of a Hewlett-Packard 5890 gas chromatograph series II equipped with a flame ionization detector
(FID). Separation was achieved on DB-5 and DB-FFAP
fused silica capillaries (each 30 m × 0.30 mm, 0.25 µm
film thickness) supplied from J&W Scientific, Folsom, CA.
The conditions used for HRGC were the same as those reported recently [17]. Compound identification was based
on comparison of calculated Retention index values, as
determined from HRGC-Olfactometry, with those of the
reference compounds on both DB-5 and DB-FFAP capillaries, and on the characteristic odor of the volatiles upon
elution from GC. MS data of the compounds were previously reported [15]
HRGC—Olfactometry
The final portion of the GC column was passed through
an unused heated block (250 ◦ C, copper insert) as reported
earlier [19]. Analysis of the concentrated flavor isolates was
done using the following dilution series: the original extract
(800 µl) was stepwise diluted (1 + 1, v/v) by addition
of methylene chloride. Aliquots of each dilution (0.5 µl)
were analyzed by GC using the DB-5 capillary column.
The potent odorants were located in the capillary effluent
by AEDA. Compound detection and odor description were
done by the author. Chromatographic conditions were the
same as those described above.
44
After sampling, the fiber was placed in the injection port
of the GC for 5 min at 230 ◦ C. The purge was off for
the first 2 min of desorption. Separation was achieved on
the above-described capillaries. Temperature program, GC
conditions, and capillary eluate sniffing were the same as
recently reported [17].
odor that is present both in the gills and skin of fish. This
corresponds to a score of 0 using the QIM. The very fresh
state is limited to 1 day of storage. We have deliberately
added subgrades (high or low) to the EU system to account
for intermediate freshness stages. Hence, after 2 days storage, hake could not be graded E with an overall low total
demerit score of 3, while after 5–6 days storage it was still
of grade A with a difference of 6–7 points in the QIM
score. This clearly illustrates as mentioned earlier [17] the
limitations of the EU system with respect to intermediate
freshness stages.
Differences in odor attributes between gills and skin appear during storage. Some faint sweet-fruity notes develop
in the skin, while neutral to acid odors can be perceived
in the gills, which both culminate in an overall pungent
odor for hake of lower sensory grades. As previously mentioned [17], use of separate odor descriptors for gills and
skin was for the purpose of relating overall odor changes
to individual potent volatiles.
Hake used in AEDA trial spoiled more rapidly as evidenced by lower sensory grades beyond 6 days storage.
Seasonal variations and onboard fish handling are among
the factors that may affect the rate of spoilage. On the basis
of sensory evaluation, hake used in both trials had a shelf
life of 7–8 days. This is in agreement with the findings
of Moral [20] who reported a preservation time of 8 days
for gutted hake stored in ice. In another study [4], whole
ungutted ice-stored Mediterranean hake (Merluccius merluccius) was acceptable for up to 9 days storage, assuming
a TMA-N value of 5 mg of N/100 g as a limit of acceptability. Longer shelf lives of between 19 and 25 days have
been reported [7], where hake had been gutted onboard and
immediately ice-stored in boxes.
Results and discussion
AEDA storage trial
Sensory evaluation
The results of AEDA of ice-stored hake volatiles are shown
in Table 3. Hake samples analyzed by this procedure represented 3 different freshness stages: S1 (grade E, QIM score
0, ∼8 h post-mortem), S2 (grade High A, QIM score 3),
and S3 (grade B, QIM score 14). Sampling time for S1
SPME headspace analysis
Extra long (2 cm) SPME fibers with 50/30 µm thickness of divinylbenzene/Carboxen/polydimethylsiloxane
(DVB/Carboxen/PDMS) coating and the manual holder
were obtained from Supelco Co. (Bellefonte, PA). Before
initial use, the fibers were conditioned for 4 h at 270 ◦ C
in the split/splitless injection port of the GC. Before each
extraction, the fiber was held at 230 ◦ C for 2 min.
Isolation of headspace from whole hake
The glass vessel recently described [17] was used for sampling headspace from whole hake. Before each sampling,
specimens of fish were taken from the polystyrene box,
and allowed to stand at room temperature while sensory
evaluation was performed. When fish reached an average
internal temperature of 15 ◦ C, it was then introduced in the
sampling vessel, the gills being maintained open by means
of an adjusted small metal clip. After the vessel had been
closed, the SPME fiber was exposed to the headspace above
fish. Exposure time was set to 15 min.
GC parameters
The results of freshness grading of ice-stored hake for the
two trials (AEDA and SPME) are shown in Table 2. Hake
in the very fresh state (grade E) has a pleasant seaweedy
Table 2
Freshness assessment of ice-stored hake (AEDA and SPME trials) by EU-grading and QIM, with emphasis on odor development
Days of storage
a
0
1
2
4
5
6
7
8
9
11
a
EU grade
AEDA
E
E
High A
A
Low A
High B
B
SPME
E
E
High A
A
Low A
QIM score
AEDA
0
0
3
7.5
9
12
14
High B
C
Odor of fish assessed just after landing
SPME
0
0
3
7.5
10
11
19
C
16
Odor description
Gills
Skin
Seaweedy
Seaweedy
Seaweedy (less intense)
Neutral, slightly acid
Slightly acid
Slightly acid
Slightly acid, pungent
Slightly acid, pungent
Acid, pungent, rancid
Acid, pungent, rancid
Seaweedy
Seaweedy
Slightly fruity
Slightly fruity, sweet
Fruity, sweet
Fruity, sweet
Fruity, slightly pungent
Fruity, slightly pungent
Pungent, rancid
Pungent, rancid
45
and S2 corresponded to the early storage stages where the
freshness concept is most relevant.
From sample S1, the original flavor extract had a slight
green-fruity odor. AEDA revealed 11 odorants in the flavor
dilution range of 16–128, of which three unknown odorants
along with (Z)-1,5-octadien-3-one showed the highest FDfactors. Among the unsaturated C6, C8, and C9 carbonyl
compounds associated with the flavor of freshly harvested
fish, only the eight carbons, mainly (Z)-1,5-octadien-3-one,
appeared as potent odorants of very fresh hake.
With the exception of a few volatiles, the overall volatile
pattern matched that of ice-stored sardine (S. pilchardus)
[17]. The main difference was, on the basis of high FDfactors, an important contribution of 3 unknown volatiles
to the flavor of hake in the early very fresh state: a low
boiling volatile with a vegetable-like odor, and two higher
boiling compounds with typical coconut and fruity odors as
perceived by sniffing. A shift in eluting times was noticed
for the latter volatiles during AEDA and between the 3 samples analyzed, but the odor character remained unchanged.
A range was therefore given for RI values on the DB-5
capillary (RI calculated from sniffing). Using the FFAP
capillary, the coconut-like volatile was detected, while the
remaining typical fruity odor lacked. It is worth mentioning
that the calculated RI value of the coconut-like volatile on
the capillary FFAP (2186) matched the reference RI value
of δ-decalactone (2184), which has the same odor character
[21]
Table 3
Volatile compounds identified in hake (M. merluccius) at different freshness stages
Compound
2,3-Pentanedione
Unknown
(Z)-3-Hexenal
(Z)-4-Heptenal
Methional
2-Acetyl-1-pyrroline
1-Octen-3-one
(Z)-1,5-Octadien-3-one
(E,Z)-3,5-Octadien-2-one
Unknown
(Z)-2-Nonenal
(E,Z)-2,6-Nonadienal
(E)-2-Nonenal
3-Methylnonane-2,4-dione
2,4,6-Nonatrienal
(E,Z)-2,4-Decadienal
(E,E)-2,4-Decadienal
Trans-4,5-epoxy-(E)-2-decenal
Unknown
Unknown
a
The flavor isolate from sample S2 exhibited a green odor
with slight fishy background notes. Compared to sample
S1, higher FD factors were determined for trans-4,5-epoxy(E)-2-decenal, followed by (Z)-4-heptenal, methional, and
2-acetyl-1-pyrroline. In contrast, 4-fold lower concentrations were found for 1-octen-3-one (Table 3). Due to the
low known thresholds of the above volatiles, their concentration changes are likely associated with the “masking” of
the faint pleasant seaweed odor of very fresh hake with development of overall fruity-sweet odors. Lower FD factors
were also found for the two unknown high boiling odorants, but for the remaining volatiles, the differences in FD
factors were within the limit of error for the AEDA method.
After 7 days of ice storage, the odor of the original flavor
extract from sample S3 was more intense and reminiscent of “fish” as compared to S2 isolate, but with slight
rancid top notes. With respect to AEDA profile, (Z)-4heptenal and (Z)-1,5-octadien-3-one showed the highest
FD factors with a 16-fold higher concentration for (Z)4-heptenal as compared to the very fresh stage (sample
S1). A concomitant 8-fold decrease in the concentration
of the vegetable-like volatile was also observed in comparison to S1. The concentration of some oxidatively derived volatiles, e.g., (E,Z)-3,5-octadien-3-one and (E,E)2,4-decadienal remained low, which indicated their minor
contribution to the overall odor of hake. The concomitant increase in the concentration of (Z)-4-heptenal and
(Z)-1,5-octadien-3-one towards 7 days of ice storage is
RIa on capillary
DB-5
740
800
898
903
912
966
975
1092
1121
1144
1150
1157
1245
1262
1306
1308
1371
1380–1398d
1385–1392d
Odor qualityb
DB-FFAP
998
1105
1142
1240
1444
1320
1293
1358
1488
1493
1565
1697
1739
1790
1993
2186
Butter-like
Vegetable-like
Green
Fatty-fishy
Boiled potato-like
Roasty, popcorn-like
Mushroom-like
Geranium-like
Fatty-fruity
Fried fat-like
Fatty-green
Cucumber-like
Cucumber-like, green
Fruity-sweet
Fatty-green
Fried fat-like
Metallic
Coconut-like
Fruity
FD-factorc
S1
S2
S3
n.d
128
8
32
n.d
n.d
32
128
16
n.d
16
16
n.d
8
16
8
32
n.d
128
128
n.d
64
8
128
16
16
8
128
32
n.d
16
8
8
8
16
n.d
64
32
32
32
8
16
8
512
8
16
8
512
32
16
16
8
n.d
8
32
8
64
32
64
16
Calculated retention index on capillaries DB-5 and DB-FFAP
Odor quality perceived at the sniffing port
c
FD-factors determined on DB-5 capillary column; n.d. not detected. Compound identification was based on the following criteria: comparison
with the reference compound on the basis of odor quality perceived at the sniffing port and the RI values on capillary DB-5 and /or FFAP
d
Range of RI where characteristic odor was perceived depending on samples
b
46
likely responsible for the “pungent” odor of hake as determined by sensory means. In ice-stored sardine of grade
high A [17], a concomitant increase in the concentration
of (Z)-4-heptenal, (Z)-1,5-octadien-3-one and of methional
correlated with the appearance of a “fishy” aroma, while
the actual overall pungent aroma of hake which lacks the
“fishiness” attribute is likely related to the lower content
of methional in hake (sample S3). Milo and Grosch [10]
determined (Z)-4-heptenal, (Z)-3-hexenal, and (Z,Z)-3,6nonadienal as being primarily responsible for the unpleasant, fishy, oily aroma of frozen-stored trout, but (Z)-4heptenal had no effect in the overall off-odor that develops
upon frozen storage of raw cod which is a lean fish [9].
SPME headspace measurements
As stated earlier, extra-long (2 cm) Carboxen/DVB/PDMS
fibers were used due to the low concentration of odor active
volatiles in the headspace above hake. A 15 min short sampling time was applied as it better approaches conventional
static headspace [22], although the less volatile compounds
are detected better with SPME.
Only 10 among 20 volatiles detected from AEDA were
perceived from SPME sniffing runs (Table 4). The sampling procedure, i.e., one fish introduced in the vessel vs. three used in AEDA, may in part explain the
fewer detected volatiles. Other factors such as the type
of fiber are to be considered as well. Using the traditional PDMS fiber, which has very high sensitivity to
non-polar compounds but not to polar compounds [22]
would have likely resulted in a different volatile pattern. Roberts et al [22] compared different fibers, using coffee and aqueous flavored solutions, and found
Table 4
SPME headspace analysis of hake volatiles at different freshness stages during ice storage
Compounda
Trimethylaminec
(Z)-4-Heptenal
Methional
2-Acetyl-1-pyroline
Dimethyl trisulfided
1-Octen-3-one
(Z)-1,5-Octadien-3-one
(E,Z)-3,5-Octadien-2-one
(E,Z)-2,6-Nonadienal
3-Methylnonane-2,4-dione
(E,E)-2,4-Decadienal
trans-4,5-epoxy-(E)-2-decenal
a
poly(dimethylsiloxane)/divinylbenzene to have the highest
overall sensitivity, while Carboxen/poly(dimethylsiloxane)
was the most sensitive to small molecules and acids.
No highly volatile odorants could be detected in the
headspace of hake. Trimethylamine was detected only after
the onset of spoilage. This is well in agreement with many
reports [4, 7]. TMA-N levels in hake remained low, until
the 12th storage day had been passed [5]. Additionally, the
increase in pH values in chilled hake during ice storage [7]
affect the volatility of TMA.
SPME headspace profile of hake in the very fresh state (E
grade) is characterized by distinct odor impressions from
the plant-like fresh volatiles, e.g., (Z)-1,5-octadien-3-one,
and from 3-methylnonane-2,4-dione and trans-4,5-epoxy(E)-2-decenal. It is worth mentioning that the vegetable-like
low-boiling volatile detected from AEDA at this stage was
not perceived during SPME headspace eluate sniffing. In
contrast, the odor intensity of some volatiles, for example
(E,Z)-2,6-nonadienal, 3-methyl-nonane-2,4-dione, and
trans-4,5-epoxy-(E)-2-decenal (Table 4) indicated a higher
contribution from these odorants to the overall odor of very
fresh hake. The dominance of the faint seaweedy-like odor
in the very fresh state could not be explained on the basis
of the SPME headspace profile. Accurate quantification of
odorants is needed to assess their actual contribution to the
whole odor impression. Nevertheless, the odor characteristics of some volatiles, mainly (E,Z)-3,5-octadien-2-one
and 3-methylnonane-2,4-dione were much consistent
with the fruity-sweet top notes perceived in the skin for
hake of grade A, as was previously found for sardine
[17]. In a similar way, the more intense odors perceived
from (Z)-4-heptenal and (Z)-1,5-octadien-3-one towards
advanced storage stages (10 < QIM score < 11) were
in agreement with the results of AEDA, and support
Odor qualityb
Amine-like, fishy
Fatty-fishy
Boiled potato-like
Roasty, popcorn-like
Cabbage-like
Mushroom-like
Geranium-like
Fatty-fruity
Cucumber-like
Fruity-sweet
Fried fat-like
Metallic
RI on capillary
DB-5
DB-FFAP
<500
896
902
908
961
964
973
1090
1151
1244
1305
1370
1107
1445
1323
1293
1361
1486
1567
1693
1793
1990
QIM score
grade E grade A
0
3
7.5
10
grade B grade C
11
16
−
++
−
−
−
++
+++
++
+++
+++
++
+++
−
+++
++
−
−
+++
++++
++++
++++
++++
+++
+++
−
++++
+++
++
−
+++
++++
+++
++
++++
+++
+++
−
++
−
−
−
+++
+++
+++
+++
+++
++
+++
−
+++
−
−
−
+++
+++
+++
+++
+++
+++
+++
++
++++
+++
+++
++++
+++
−
+++
−
++++
+++
+++
Compound identification based on the criteria reported in Table 3
Odor quality of the compound perceived at the sniffing port; intensity of odor was evaluated using the following scale: ++++, very intense
odor; +, slightly perceived odor; −, odorless at the sniffing port. Results are expressed as the mean of two sniffing runs
c
The compound was identified by comparing it with the reference substance on the basis of the following criteria: retention time on the
capillary DB-5 and odor quality perceived at the sniffing port
d
Tentative identification from characteristic odor and RI value on the basis of work by Guth and Grosch [25]
b
47
our assumption that the increase in the concentration
of both volatiles is likely responsible for the overall
“acid-pungent” odor that develops in hake after prolonged
ice-storage. The higher odor intensity of (Z)-4-heptenal
from hake of grade B (Table 4) and the concomitant
apparent decrease in the intensity of the cucumber-like
odor from (E,Z)-2,6-nonadienal is in concordance with the
reported retro-aldol condensation mechanism of formation
of (Z)-4-heptenal from (E,Z)-2,6-nonadienal [23].
Among the volatiles which have been shown to contribute
to microbial spoilage odors of fish, only trimethylamine
and dimethyl trisulfide were detected from spoiled hake
using SPME headspace. Dimethyl trisulfide has an odor
threshold of 0.04 ppb in water [24]. It was found to be the
most potent odorant of boiled Cod (Gadus morhua) after
prolonged frozen storage [12].
Conclusion
Hake in the very fresh state has a faint seaweedy odor. The
corresponding AEDA profile revealed, in addition to (Z)1,5-octadien-3-one, three unknown volatiles as being the
most potent odorants at this stage. Subsequent loss in freshness with development of overall fruity and sweet odors
could be, in part, instrumentally related to the higher concentrations determined for trans-4,5-epoxy-(E)-2-decenal,
(Z)-4-heptenal, methional, and 2-acetyl-1-pyrroline, while
on the basis of the results of both AEDA and SPME
headspace, the pungent odor of hake at a lower sensory
grade (B) was likely to be caused by the concomitant increase in the concentration of (Z)-4-heptenal and of (Z)1,5-octadien-3-one.
Using SPME headspace measurements of the volatiles
from ice-stored hake, no highly volatile odorants could
be detected. In contrast to AEDA, a higher contribution from (E,Z)-2,6-nonadienal, 3-methyl-nonane-2,4dione, and trans-4,5-epoxy-(E)-2-decenal to the overall
odor of very fresh hake was found. Intensity and odor characteristics of some volatiles, for example 3-methylnonane2,4-dione, were closely related to overall skin odor changes.
Trimethylamine and dimethyl trisulfide were detected in
spoiled hake by this method.
The flavor isolation method applied in AEDA (vacuum distillation) allowed the detection of two low boiling
volatiles as being important odorants of hake flavor, mainly
in the very fresh state (grade E).
Acknowledgments Special thanks are due to Prof. P. Schieberle
(Deutsche Forchungsanstalt für Lebensmittelchemie, Garching,
Germany) for providing reference samples and for assistance in the
manufacturing of glass vessels. We gratefully acknowledge the International Foundation for Science (Stockholm, Sweden) for financially
supporting the present work
References
1. Anonymous (2001) Eurofish 6:55–59
2. Luten JB, Martinsdottir E (1997) In: International institute of
refrigeration (ed) Methods to determine the freshness of fish in
research and industry, proceedings of the final meeting of the
concerted action “evaluation of fish freshness” AIR3CT942283;
Nantes Conference, Paris, France, pp 287–296
3. Ruiz-Capillas C, Morales J, Moral A (2001) J Sci Food Agric
81:551–558
4. Baixas-Nogueras S, Bover-Cid S, Vidal-Carou MC, VecianaNogués MT, Marine-Font A (2001) J Agric Food Chem
49:1681–1686
5. Ruiz-Capillas C, Moral A (2001) J Food Sci 66(7):1030–1032
6. Medina I, Aubourg S, Gallardo JM (2000) Eur Food Res
Technol 210:353–358
7. Ruiz-Capillas C, Moral A (2001) Food Res Int 34:441–447
8. Ólafsdóttir G, Martinsdóttir E, Oehlenscläger J, Dalgaard P,
Jensen B, Undeland I, Mackie IM, Henehan G, Nielsen J, Nilsen
H (1997) Trends Food Sci Technol 8:258–265
9. Milo C, Grosch W (1997) In: Shahidi F, Cadwallader K (eds)
Flavor and lipid chemistry of seafoods. ACS Symposium Series
674. American Chemical Society, Washington, DC, pp 110–
119
10. Milo C, Grosch W (1993) J Agric Food Chem 41:2076–2081
11. Milo C, Grosch W (1996) J Agric Food Chem 44:2366–2371
12. Milo C, Grosch W (1995) J Agric Food Chem 43:
459–462
13. Anonymous (1996) Official J European Communities No.
L334/1-14, 23.12.96
14. Grosch W (1994) Flavour Fragrance J 9:147–158
15. Triqui R, Guth H (1997) In: Shahidi F, Cadwallader K (eds)
Flavor and lipid chemistry of seafoods. ACS Symposium
Series 674. American Chemical Society, Washington, DC, pp
31–38
16. Nunes M, Personal communication, Instituto de Investigação
das Pescas e do Mar (IPIMAR), Avenida de Brasilia, 1449–006
Lisboa, Portugal
17. Triqui R, Bouchriti N (2003) J Agric Food Chem 51:
7540–7546
18. Sen A, Laskawy G, Schieberle P, Grosch W (1991) J Agric
Food Chem 39:757–759
19. Triqui R, Reineccius GA (1995) J Agric Food Chem 43:1883–
1889
20. Moral A (1989) Alimentaria 288:29–38
21. Schieberle P, Gassenmeier H, Guth H, Sen A, Grosch W (1993)
Lebensm Wiss U Technol 26:347–356
22. Roberts DB, Pollien P, Milo C (2000) J Agric Food Chem
48:2430–2437
23. Josephson DB, Lindsay RC (1987) J Am Oil Chem Soc
64:132–138
24. Buttery RG, Guadagni DG, Ling LC, Seifert RM, Lipton W
(1976) J Agric Food Chem 24(4):829–832
25. Guth H, Grosch W (1994) J Agric Food Chem 42:
2862–2866