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INFLUENCE OF STORAGE TIME AND TEMPERATURE ON LIPID
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DETERIORATION DURING COD (Gadus morhua) AND HADDOCK
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Melanogrammus aeglefinus) FROZEN STORAGE
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Santiago P. Aubourg* and Isabel Medina
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Instituto de Investigaciones Marinas (CSIC)
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c/ Eduardo Cabello, 6
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36208-Vigo (Spain)
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*Author to whom correspondence should be addressed
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[telephone +34 986 231930; fax +34 986 292762; e-mail: saubourg@iim.csic.es]
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ABSTRACT
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Lean fish deterioration during frozen storage (-30C and -10C) up to one year
4
was studied by lipid changes assessment. Comparison between a formaldehyde (FA)-
5
forming (cod) and a FA-non forming (haddock) species was carried out. Lipid damages
6
were measured on the basis of free fatty acids (FFA), peroxide value (PV),
7
thiobarbituric acid index (TBA-i) and fluorescent compounds. In both species, at -30ºC
8
most lipid damage indices showed significant correlations with the storage time.
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However, at -10ºC, only the FFA and fluorescence detections provided significant
10
correlations with the storage time. Comparison between the fish species showed higher
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lipid oxidation (PV and TBA-i) and hydrolysis (FFA content) in haddock than in cod at
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–10ºC; however, a higher fluorescence development was observed in cod at the same
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temperarure. At –30ºC little differences in lipid damage indices were detected between
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both species.
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Running Title: Lipid deterioration in frozen lean fish.
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Key Words: Formaldehyde, frozen storage, gadoids, lean fish, lipid oxidation and
hydrolysis.
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2
INTRODUCTION
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Processed fish and other marine species are products of great economic
4
importance in many countries. During processing and storage fish quality may decline
5
as a result of several factors. One of the most important concerns the oxidation of the
6
highly unsaturated lipids directly related to the production of off flavours and odours in
7
foods (Pearson et al., 1977; Pigott and Tucker, 1987).
8
During frozen storage of lean fish such as gadoid species most attention has been
9
given to the formaldehyde (FA) formation and its implication in quality loss (Shenouda,
10
1980; Rehbein, 1988). However, lipid hydrolysis and oxidation have been shown to
11
occur during the lean fish frozen storage and become an important factor of fish
12
acceptance as influencing protein denaturation, texture changes, functionality loss and
13
fluorescence development (Davies and Reece, 1982; Mackie, 1993; Sotelo et al., 1995).
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The relative influence of FA and lipid degradation products in texture changes has been
15
evaluated (Rehbein and Orlick, 1990; Careche and Tejada, 1994) and the participation
16
of FA in the interaction compounds formation with fluorescent properties has been
17
recently reported (Aubourg, 1998a, 1998b).
18
In the present work the influence of time (up to one year) and temperature (-
19
10ºC and –30ºC) on lipid deterioration produced during the frozen storage of lean fish
20
was studied. Detection of primary and secondary lipid oxidation products, interaction
21
compounds and lipid hydrolysis were carried out. Comparison between a FA-forming
22
fish species (cod) and a FA-non forming one (haddock) (Mackie, 1993; Howell et al.,
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1996) was undergone to study the effect that FA formed during the frozen storage may
24
have on the lipid deterioration.
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3
MATERIALS AND METHODS
1
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3
Raw material, processing and sampling
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Fresh cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) were
5
purchased at a public market. Individual fish were eviscerated, beheaded, filleted and
6
frozen at -40C. The fish fillets (145-160g each, in both species) were then distributed
7
into two storage temperatures: -30C and -10C. For each storage temperature and each
8
fish species, fillets were divided into three batches, which were studied separately
9
during the whole experiment. Analyses on cod and haddock fish were carried out on the
10
homogenised white muscle of the raw material employed and at 1, 3, 5, 7, 9 and 12
11
months of frozen storage.
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13
Water and lipid contents
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Water content was determined by weight difference of the homogenised muscle
15
(1-2 g) before and after 24 hours at 105C. Results were calculated as g water per kg
16
muscle. Lipids were extracted by the Bligh and Dyer (1959) method. Results were
17
calculated as g lipid per kg wet muscle.
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Lipid damage measurements
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Free fatty acids (FFA) content was determined by the Lowry and Tinsley (1976)
21
method based on complex formation with cupriacetate-pyridine. Results are expressed
22
as g FFA per kg lipids.
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Peroxide value (PV) expressed as meq oxygen per kg lipids was determined by
the ferrithiocyanate method (Chapman and McKay, 1949).
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1
2
3
4
The thiobarbituric acid index (TBA-i) (mg malondialdehyde per kg sample) was
determined according to Vyncke (1970).
All spectrophotometric determinations were carried out using a Beckman DV-64
spectrophotometer.
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Fluorescence formation (Perkin-Elmer LS 3B) at 393/463 nm and 327/415 nm
6
was studied according to previous experience (Aubourg and Medina, 1997; Aubourg et
7
al., 1998). The relative fluorescence (RF) was calculated as follows: RF = F/Fst, where F
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is the sample fluorescence at each excitation/emission maximum, and Fst is the
9
corresponding fluorescence intensity of a quinine sulphate solution (1 g ml-1 in 0.05 M
10
H2SO4) at the corresponding wavelength. The fluorescence shift (F) was calculated as
11
the ratio between both RF values: F = RF393/463nm / RF327/415nm, and was analysed on the
12
aqueous (Faq) and organic (For) phases resulting from the lipid extraction (Bligh and
13
Dyer, 1959).
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Statistical analysis
Data from the different lipid damage measurements were subjected to the
ANOVA one-way method and correlation analysis (p < 0.05) (Statsoft, 1994).
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RESULTS
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Water contents ranged between 791 and 832 g per kg in cod and between 793
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and 821 g per kg in haddock. Lipid contents ranged between 4.5 and 6.5 g per kg, for
5
1
both cod and haddock. No significant differences (p < 0.05) were obtained in both
2
parameters as a result of the time and temperature of frozen storage.
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4
Lipid hydrolysis (Tables 1-4)
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A great hydrolytic activity was observed in both fish species. The preservative
6
effect of the storage temperature was evident since -30C sample values were lower
7
than the corresponding -10C ones. As a general behaviour, the FFA formation was
8
faster during the first steps of the storage. At the end of the storage time a lower
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(p<0.05) FFA level was obtained in the case of cod than haddock at both temperatures.
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Haddock provided a progressive increase with time of storage at both
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temperatures, until month 7 at -30ºC and until month 9 at -10ºC; after those time
12
storages, no significant differences were observed. Cod showed at -10C an increase till
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month 5, and then no more differences till the end; however, at -30C an increase till
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month 7 was followed by a decrease at the end of the storage.
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Lipid oxidation (Tables 1-4)
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The PV provided a gradual increase along the whole storage in both species at -
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30C; however, values obtained at the end of the storage (7.9 and 8.5 for cod and
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haddock, respectively) remained relatively low (Pérez-Villarreal and Howgate, 1991;
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Vidya Sagar Reddy et al., 1992) as a result of the preservative effect of the storage
21
temperature on the fillets. A faster PV development was obtained at -10C in both
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species; for cod, an increase at month 3 was followed by no variations till month 9 and a
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decrease at the end of the storage. In the case of haddock, increases were observed at
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months 3 and 9 followed by a sharp decrease at the end of the storage. PV comparison
6
1
of both fish species during the increasing period (months 3, 5, 7 and 9) showed a
2
significantly (p<0.05) higher primary oxidation for haddock than cod at -10C.
3
Secondary lipid oxidation was studied by the TBA-i. As a general rule, little
4
significant differences were observed. Values obtained along the whole experiment
5
were relatively low, specially compared to those obtained in fatty fish species (Kurade
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and Baranowski, 1987; Aubourg et al., 1998).
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At -30ºC the highest values were obtained at month 9 in haddock and at the end
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of the storage in cod. At -10ºC, both species showed the highest values at month 5,
9
being higher in haddock than cod; then, a decrease in the formation of thiobarbituric
10
acid (TBA) reactive substances was observed that could be explained as a result of
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combining with proteins to form polymers (Orlick et al., 1991; Vidya Sagar Reddy et
12
al., 1992).
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Interaction compounds formation (Tables 1-4)
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Interaction compounds formation was studied by means of fluorescent
16
properties, according to previous research (Aubourg and Medina, 1997; Aubourg et al.,
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1998).
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The organic phase (lipid extract) study provided very little significant
19
differences along the first steps of storage (months 1, 3 and 5) in both species at both
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temperatures. In all cases, the highest values were obtained at month 7 and were
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followed by a decrease at the end of the storage time. Significant differences between
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both fish species were only obtained at month 7, with a higher For value for haddock
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than cod. As a result of the storage temperature, higher For values at -10C than at -
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30C were obtained in the two latest storage times (months 9 and 12).
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1
A clearer trend was obtained by analysis of the aqueous phase (Faq) resulting
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from the lipid extraction. No significant variations were observed during the first five
3
months of storage at both temperatures in both species. After this induction period,
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higher values were obtained at -10C than at -30C in the two latest storage times
5
(months 9 and 12). At -10ºC a big increase was observed in both species at month 9. At
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-30ºC some increases were also observed (month 9 for cod and month 7 for haddock).
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Comparison of both fish species at -10C showed that a higher Faq value was
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produced in cod than in haddock from month 5 till the end. Little differences between
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both species were obtained at -30C.
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12
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Correlation analyses
The different quality measurements were tested for correlation with storage time
and also with each other (Tables 5-6, cod; Tables 7-8, haddock).
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According to results at –30ºC (Tables 1 and 3), all indices except for For
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showed significant (p<0.05) linear correlation values with the storage time (Tables 5
16
and 7). As lipid degradation increased (-10ºC samples; Tables 2 and 4), some indices
17
(PV and TBA-i) showed lower correlation values with the storage time; the best linear
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correlations were then obtained for the FFA and Faq values (Tables 6 and 8).
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Values obtained for FFA and Faq at both temperatures and in both fish species
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were also studied by nonlinear fittings. In most cases, the nonlinear model was better
21
than the linear one (exponential for Faq and logarithmic for FFA; Tables 5-8),
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according to the slopes showed in Figures 1 (cod) and 2 (haddock).
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Comparison of the different lipid damage indices between each other provided
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some significant correlation values, although most results were not satisfactory. It can
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be argued that the three lipid oxidation indices (PV, TBA-i and Faq) assess damage at
8
1
different steps of the whole oxidation mechanism; while hydrolysis (FFA formation)
2
follows a different pathway than oxidation. FFA and Faq indices showed, however,
3
significant correlation values at both temperatures and in both species.
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5
6
7
DISCUSSION
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The preservative effect of temperature on lipid damage was evident in both fish
10
species. Lipid hydrolysis (FFA content) and oxidation (PV and TBA-i) and interaction
11
compound formation (Faq) showed a higher development at -10ºC than at -30ºC.
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Both the FFA content and Faq value have shown satisfactory correlation values
13
with the storage time at both temperatures tested. Reliability of the remaining indices
14
showed to decrease when considering the -10ºC temperature. As an explanation,
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degradation products that are susceptible to be measured in such indices (peroxides,
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TBA reactive substances) can either be destroyed or interact with other constituents, so
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that the determination cannot always afford an accurate method for the quality changes
18
assessment (Melton, 1983; Smith et al., 1990). Thus, correlation values of the different
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indices between each other did not provide satisfactory results.
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According to the general theory, lipid oxidation compounds have reacted with
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nucleophilic biological constituents (Pokorný, 1977; Gardner, 1979; Howell, 1995) and
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caused the formation of interaction compounds with fluorescent properties. Its detection
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by the Faq value has provided a good assessment of quality changes, according to
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previous research where fatty fish processing (frozen storage, chilling and canning) was
25
tested (Aubourg and Medina, 1997; Aubourg et al., 1998).
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1
At the same time, hydrolytic activity also showed to be sensitive with the time of
2
storage at both temperatures. Previous experiments on frozen storage of lean fish had
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already shown this kind of damage determination as a valuable tool in order to assess
4
quality (Quaranta and Pérez, 1983; de Koning and Mol, 1991).
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Formation of FFA itself does not lead to nutritional losses. However, it has been
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proved that accumulation of FFA in frozen fish is related in some extent with lack of
7
acceptability of frozen fish, because FFA are known to cause texture deterioration by
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interacting with proteins (Shenouda, 1980; Rehbein, 1988; Sotelo et al., 1995) and have
9
shown to be strongly interrelated with lipid oxidation (Miyashita and Takagi, 1986; Han
10
and Liston, 1988).
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Another aspect studied in the present experiment was the comparison of lipid
12
damages between a FA-forming species (cod) and a FA-non forming (haddock) one. In
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a previous experiment (Howell et al., 1996), cod and haddock fillets were stored at –
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20ºC and –30ºC. As a result, formation of dimethylamine (DMA) and FA was only
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confirmed at –20ºC in cod and not in haddock; at –30ºC neither of both fish species
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produced DMA nor FA, according to other experiment (Pérez-Villarreal and Howgate,
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1991). In the present work, little differences in the lipid oxidation and hydrolysis
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development between both species were obtained at –30ºC. However, at –10ºC, when
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FA is suposed to be produced in cod (Howell et al., 1996), a higher lipid oxidation (PV
20
and TBA-i) and hydrolysis (FFA) development was observed in haddock than in cod.
21
Result on a previous report at –10ºC concerning dehydrated samples showed that
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haddock produced a higher pentenal content and PV than cod (Hardy and McGill,
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1990).
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Previous results have suggested an inhibition of FA and DMA formation due to
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the presence of oxidised lipid in a FA-forming species (hake) during frozen storage
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1
(Careche and Tejada, 1990; Joly et al., 1997). However, no information is available
2
related to the effect of FA on enzymes responsible for lipid hydrolysis (lipases,
3
phospholipases) and oxidation (lipoxygenases, oxidases), although FA has shown to
4
react easily with proteins and led to protein denaturation in FA-forming fish (Rehbein,
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1988; Mackie, 1993).
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Higher Faq values were obtained in the case of cod than haddock at –10ºC. This
7
result agrees with previous experiments where it was concluded that the presence of FA
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would enhance the fluorescent compounds formation by participating in the interaction
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compounds development between lipid oxidation compounds and amine biological
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constituents (Aubourg, 1998a; Aubourg, 1998b). However, a great diversity of
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molecules (aldehydes, amines, and so on) could be involved in the fluorescent
12
compounds formation, so that the entire difference in fluorescence development
13
between both species should not be explained as a result of FA presence (Aubourg and
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Gallardo, 1997; Aubourg, 1998c).
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CONCLUSIONS
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From the present results, fluorescence detection (Faq value) of interaction
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compounds formed during the frozen storage of two lean fish species showed to be
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sensible to quality changes along the storage. Correlation values with the storage time
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showed to be as good as the FFA determination.
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Lipid damage measurements have shown differences at –10ºC between both fish
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species. Haddock showed to be more susceptible to lipid oxidation (PV and TBA-i) and
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1
hydrolysis (FFA) development than cod. Some complementary research should be
2
carried out in order to assess the interaction between FA and oxidative and hydrolytic
3
enzymes during the frozen storage of FA-forming fish species, and evaluate the relative
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incidence of this interaction on the general lipid degradation mechanism. Complemntary
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research also should be carried out to assess the different pathways of FA-lipid
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oxidation compounds-nucleophilic compounds interaction and the relative effect of each
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kind of compound in the total fluorescence formation.
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ACKNOWLEDGMENTS
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We thank Mr. Marcos Trigo and Mrs. Montserrat Martínez for technical
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assistance, Dr. Paul Reece for providing the fish samples and the European Community
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for financial support of the Research Project FAIR-CT95-1111 (1996-1999).
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REFERENCES
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to fish deterioration. Z. Lebensm. Unters. Forsch. 206 29-32.
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deterioration. Z. Lebensm. Unters. Forsch. 207 268-272.
Aubourg, S. 1998c. Fluorescence detection in aldehyde containing model systems:
Relationship with fish deterioration. Grasas y Aceites 49 419-424.
Aubourg, S. and Gallardo, J. 1997. Fluorescence changes in amine model systems
related to fish deterioration. Int. J. Food Sci. Technol. 32 153-158.
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Aubourg, S. and Medina, I. 1997. Quality differences assessment in canned sardine
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(Sardina pilchardus) by detection of fluorescent compounds. J. Agric. Food
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Chem. 45 3617-3621.
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Aubourg, S., Sotelo, C. and Pérez-Martín, R. 1998. Assessment of quality changes in
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frozen sardine (Sardina pilchardus) by fluorescence detection. J. Am. Oil Chem.
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Soc. 75 575-580.
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Bligh, E. and Dyer, W. 1959. A rapid method of total extraction and purification. Can.
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Careche, M. and Tejada, M. 1990. The effect of neutral and oxidised lipids on
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functionality in hake (Merluccius merluccius L.): A dimethylamine- and
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formaldehyde-forming species during frozen storage. Food Chem. 36 113-128.
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Careche, M. and Tejada, M. 1994. Hake natural actomyosin interaction with free fatty
acids during frozen storage. J. Sci. Food Agric. 64 501-507.
Chapman, R. and McKay, J. 1949. The estimation of peroxides in fats and oils by the
ferric thiocyanate method. J. Am. Oil Chem. Soc. 26 360-363
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Davies, H. and Reece, P. 1982. Fluorescence of fish muscle: causes of change occurring
during frozen storage. J. Sci. Food Agric. 33 1143-1151.
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de Koning, A. and Mol, T. 1991. Quantitative quality tests for frozen fish: soluble
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protein and free fatty acid content as quality criteria for hake (Merluccius
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merluccius) stored at -18C. J. Sci. Food Agric. 54 449-458.
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Gardner, H. 1979. Lipid hydroperoxide reactivity with proteins and amino acids: A
review. J. Agric. Food Chem. 27 220-229.
Han, T. and Liston, J. 1988. Correlation between lipid peroxidation and phospholipid
hydrolysis in frozen fish muscle. J. Food Sci. 53 1917-1918.
Hardy, R. and McGill, A. 1990. The influence of cold-storage dehydration on the
oxidation of white fish. I.I.F.- I.I.R.- Commission E2, Aberdeen (UK), pp. 1-5.
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Howell, N. 1995. Interaction of proteins with small molecules. In Ingredient
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interactions -Effects on food quality, ed. Gaoucar, A. Marcel Dekker, New York
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(USA), pp. 269-289.
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Howell, N., Shavila, Y., Grootveld, M. and Williams, S. 1996. High-resolution NMR
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and magnetic resonance imaging (MRI) studies on fresh and frozen cod (Gadus
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morhua) and haddock (Melanogrammus aeglefinus). J. Sci. Food Agric. 72 49-
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56.
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Joly, A., Huidobro, A. and Tejada, M. 1997. Influence of lipids on dimethylamine
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formation in model systems of hake (Merluccius merluccius) kidney during
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frozen storage. Z. Lebensm. Unters. Forsch. 205 14-18.
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Kurade, S. and Baranowski, J. 1987. Prediction of shelf-life of frozen minced fish in
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terms of oxidative rancidity as measured by TBARS number. J. Food Sci. 52
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300-302, 311.
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Lowry, R. and Tinsley, I. 1976. Rapid colorimetric determination of free fatty acids. J.
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Mackie, I. 1993. The effects of freezing on flesh proteins. Food Rev. Int. 9 575-610.
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Melton, S. 1983. Methodology for following lipid oxidation in muscle foods. Food
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Technol. 37 105-111, 116.
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of free fatty acids. J. Am. Oil Chem. Soc. 63 1380-1384.
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Orlick, B., Oehlenschläger, J. and Schreiber, W. 1991. Changes in lipids and
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nitrogenous compounds in cod (Gadus morhua) and saithe (Pollachius virens)
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during frozen storage. Arch. Fisch. Wiss. 41 89-99.
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Pérez-Villarreal, B. and Howgate, P. 1991. Deterioration of European hake (Merluccius
merluccius) during frozen storage. J. Sci. Food Agric. 55 455-469.
Pigott, G. and Tucker, B. 1987. Science opens new horizons for marine lipids in human
nutrition. Food Rev. Int. 3 105-138.
Pokorný, J. 1977. Interactions of oxidized lipids with proteins. Riv. Ital. Sostanze
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Quaranta, H. and Pérez, S. 1983. Chemical methods for measuring changes in freeze
stored fish: A review. Food Chem. 11 79-85.
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Rehbein, H. 1988. Relevance of trimethylamine oxide demethylase activity and
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haemoglobin content to formaldehyde production and texture deterioration in
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frozen stored minced fish muscle. J. Sci. Food Agric. 43 261-276.
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Rehbein, H. and Orlick, B. 1990. Comparison of the contribution of formaldehyde and
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lipid oxidation products to protein denaturation and texture deterioration during
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frozen storage of minced ice-fish fillet (Champsocephalus gunnari and
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Pseudochaenichthys georgianus). Int. J. Refrig. 13 336-341.
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Shenouda, S. 1980. Theories of protein denaturation during frozen storage of fish flesh.
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Sotelo, C., Piñeiro, C. and Pérez-Martín, R. 1995. Review. Denaturation of fish proteins
8
during frozen storage: Role of formaldehyde. Z. Lebensm. Unters. Forsch. 200
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14-23.
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Statsoft. 1994. Statistica for Macintosh; Statsoft and its licensors, Tulsa, Oklahoma
(USA).
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pink perch mince during frozen storage. Int. J. Food Sci. Technol. 27 271-276.
14
Vyncke, W. 1970. Direct determination of the thiobarbituric acid value in trichloracetic
15
acid extracts of fish as a measure of oxidative rancidity. Fette Seifen Anstrichm.
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72 1084-1087.
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FIGURE LEGENDS
1
2
3
4
5
6
7
Figure 1:
8
Changes in FFA content (Fig. 1A) and Faq value (Fig. 1B) during cod frozen
9
storage. Mean value and standard deviation are expressed.
10
11
12
13
14
Figure 2:
15
Changes in FFA content (Fig. 2A) and Faq value (Fig. 2B) during haddock
16
frozen storage. Mean value and standard deviation are expressed.
17
18
19
17
TABLE 1: Lipid damage measurement* during cod frozen (-30C) storage**
ST

FFA

PV

TBA-i

For

Faq

0
71.4 ab
2.0 a
0.11 a
0.75 ab
0.82 a
1
58.9 a
2.6 a
0.12 a
0.83 b
1.03 ab
3
94.2 ab
2.8 a
0.38 b
0.64 ab
0.98 a
5
104.9 bc
3.7 ab
0.39 b
0.67 ab
1.17 ab
7
195.0 d
3.4 ab
0.19 a
1.43 c
1.48 ab
9
185.6 d
5.2 b
0.41 b
0.60 ab
5.87 c
12
143.1 c
7.9 c
0.49 b
0.50 a
4.75 bc
* Means of three independent determinations. Values in the same column followed by
different letters are significantly different (p<0.05).
** Abbreviations and units: ST (storage time; months), FFA (free fatty acids; g FFA
kg-1 lipids), PV (peroxide value; meq oxygen kg-1 lipids), TBA-i (thiobarbituric
acid index; mg malondialdehyde kg-1 sample), For (fluorescence shift in organic
phase) and Faq (fluorescence shift in aqueous phase) (fluorescence
determinations calculated as expressed in the Materials and Methods section).
TABLE 2: Lipid damage measurement* during cod frozen (-10C) storage**
ST

FFA

PV

TBA-i

For

Faq

0
71.4 a
2.0 a
0.11 ab
0.75 a
0.82 a
1
268.0 b
3.3 a
0.10 ab
0.69 a
1.07 a
3
394.9 c
6.5 b
0.43 d
0.66 a
1.04 a
5
510.0 de
6.7 b
0.61 e
1.07 ab
1.44 ab
7
451.3 cd
6.2 b
0.07 a
1.26 b
6.82 b
9
556.8 de
7.8 b
0.28 cd
1.00 ab
15.78 c
12
488.4 d
1.7 a
0.26 bc
1.05 ab
17.87 c
* Means of three independent determinations. Values in the same column followed by
different letters are significantly different (p<0.05).
** Abbreviations and units as indicated in Table 1.
19
TABLE 3: Lipid damage measurement* during haddock frozen (-30C) storage**
ST

FFA

PV

TBA-i

For

Faq

0
89.6 a
1.8 a
0.26 ab
0.77 a
0.62 a
1
93.8 a
3.2 a
0.17 a
0.69 a
0.80 a
3
151.3 bc
3.0 a
0.35 b
0.79 a
0.78 a
5
122.1 ab
5.2 b
0.45 b
0.80 a
0.78 a
7
189.4 cd
5.8 bc
0.42 b
2.10 b
4.88 b
9
210.4 d
7.6 cd
0.66 c
0.78 a
3.34 ab
12
211.1 d
8.5 d
0.42 b
0.67 a
5.51 b
* Means of three independent determinations. Values in the same column followed by
different letters are significantly different (p<0.05).
** Abbreviations and units as indicated in Table 1.
20
TABLE 4: Lipid damage measurement* during haddock frozen (-10C) storage**
ST

FFA

PV

TBA-i

For

Faq

0
89.6 a
1.8 a
0.26 a
0.77 a
0.62 a
1
296.0 b
7.2 ab
0.18 a
0.79 a
0.83 a
3
475.9 c
8.5 b
0.60 ab
1.19 a
0.97 a
5
449.7 c
9.6 b
0.81 b
1.13 a
0.78 a
7
464.7 c
8.6 b
0.30 a
1.75 b
1.13 a
9
555.8 d
30.5 c
0.61 ab
1.85 b
6.66 b
12
542.4 d
0.8 a
0.31 a
1.02 a
10.94 b
* Means of three independent determinations. Values in the same column followed by
different letters are significantly different (p<0.05).
** Abbreviations and units as indicated in Table 1.
21
TABLE 5: Linear correlation matrix* for different parameters (storage time and lipid
damage indices) measured during cod frozen (-30ºC) storage**
ST
PV

TBA-i

FFA

For

Faq

0.83*
0.67*
0.71*
(0.75*)
-0.05
0.66*
(0.74*)
0.69*
0.33
-0.32
0.54*
0.22
-0.50*
0.46
0.37
0.51*
PV
TBA-i
FFA
For
-0.24
* Significant (p<0.05) values.
** Abbreviations as specified in Table 1. Results in brackets correspond to nonlinear
fittings (logarithmic for FFA; exponential for Faq).
22
TABLE 6: Linear correlation matrix* for different parameters (storage time and lipid
damage indices) measured during cod frozen (-10ºC) storage**
ST
PV

TBA-i

FFA

For

Faq

0.17
0.17
0.79*
(0.91*)
0.46*
0.88*
(0.91*)
0.39
0.61*
0.24
0.02
0.44
0.09
-0.01
0.38
0.54*
PV
TBA-i
FFA
For
0.43
* Significant (p<0.05) values.
** Abbreviations as specified in Table 1. Results in brackets correspond to nonlinear
fittings (logarithmic for FFA; exponential for Faq).
23
TABLE 7: Linear correlation matrix* for different parameters (storage time and lipid
damage indices) measured during haddock frozen (-30ºC) storage**
ST
PV

TBA-i

FFA

For

Faq

0.93*
0.66*
0.85*
(0.84*)
0.14
0.70*
(0.78*)
0.55*
0.67*
0.20
0.61*
0.77*
0.08
0.33
0.23
0.68*
PV
TBA-i
FFA
For
0.46*
* Significant (p<0.05) values.
** Abbreviations as specified in Table 1. Results in brackets correspond to nonlinear
fittings (logarithmic for FFA; exponential for Faq).
24
TABLE 8: Linear correlation matrix* for different parameters (storage time and lipid
damage indices) measured during haddock frozen (-10ºC) storage**
ST
PV

TBA-i

FFA

For

Faq

0.26
0.16
0.84*
(0.93*)
0.51*
0.74*
(0.81*)
0.40
0.43
0.66*
0.13
0.36
0.30
-0.07
0.58*
0.53*
PV
TBA-i
FFA
For
0.10
* Significant (p<0.05) values.
** Abbreviations as specified in Table 1. Results in brackets correspond to nonlinear
fittings (logarithmic for FFA; exponential for Faq).
25
TABLE 5: Linear correlation values for the storage time and the different lipid
indices** during the frozen storage (-30C and -10C) of both species (cod and
haddock)***
Measurement

Fish species
(frozen storage temperature)

Cod
(-30C)

Cod
(-10C)

Haddock
(-30C)

Haddock
(-10C)

FFA
0.71*
(0.75*)
0.79*
(0.91*)
0.85*
(0.84*)
0.84*
(0.93*)
PV
0.83*
0.17
0.93*
0.26
CD
0.65*
0.59*
0.72*
0.55*
TBA-i
0.67*
0.17
0.66*
0.16
For
-0.05
0.46*
0.14
0.51*
Faq
0.66*
(0.74*)
0.88*
(0.91*)
0.70*
(0.78*)
0.74*
(0.81*)
* Significant (p<0.05) values.
** Abbreviations as specified in Table 1.
*** Results in brackets correspond to nonlinear fittings (logarithmic for FFA and ST;
exponential for Faq and ST).
26