Effect of previous chilled storage on rancidity development in frozen horse mackerel Trachurus trachurus Santiago P Aubourg,1* Ines Lehmann2 and Jose´ M Gallardo1 1 Instituto de Investig
Trang 1Effect of previous chilled storage on rancidity development in frozen horse mackerel
(Trachurus trachurus)
Santiago P Aubourg,1* Ines Lehmann2 and Jose´ M Gallardo1
1
Instituto de Investigaciones Marinas (CSIC), Eduardo Cabello 6, E-36208 Vigo, Spain
2Bundesforschunganstalt fu¨r Fischerei, Institut fu¨r Fischereitechnik und Fischqualita¨t, Palmaille 9, D-22767 Hamburg, Germany
Abstract: Rancidity development during frozen storage ( 20°C) of an underutilised medium-fat-content fish species, horse mackerel (Trachurus trachurus), was studied Special attention was given
to the effect of previous chilled storage (0, 1, 3 and 5 days) on the quality of the frozen fish For this, chemical (free fatty acid and conjugated diene contents; peroxide value, PV; thiobarbituric acid index, TBA-i; fluorescent compound formation) and sensory (rancid odour and taste) analyses were carried out Hydrolytic rancidity showed an increase with frozen storage time; however, no effect of previous chilling time was observed on the frozen product Oxidative rancidity measured by chemical (PV, TBA-i and fluorescence) and sensory (odour and taste) indices increased with frozen storage time and also with previous chilling time Satisfactory quality was maintained up to 7 months of frozen storage
of horse mackerel provided that a short chilling time (not longer than 3 days) was employed
#2002 Society of Chemical Industry
Keywords:underutilised fish; chilling; frozen storage; chemical and sensory analyses; rancidity; shelf-life
INTRODUCTION
Fish and other marine species give rise to products of
great economic importance in many countries The
fish industry is actually suffering from dwindling
stocks of traditional species as a result of drastic
changes in their availability Thus fish technologists
and the fish trade have turned their attention to some
unconventional sources of raw material.1,2One such
species is horse mackerel (Trachurus trachurus), a
medium-fat-content fish abundant in the Northeast
Atlantic.3,4Efforts have been made to utilise it in the
manufacture of several smoked,5 canned,6 frozen7,8
and restructured9fish products
During processing and storage, fish quality may
decline as a result of several factors One of the most
important is oxidation of highly unsaturated lipids,10
which is directly related to the production of
off-flavours and odours.11,12 Frozen storage has been
widely employed to maintain fish properties before
consumption or use in other technological
pro-cesses.13,14 However, during frozen storage of fish,
lipid hydrolysis and oxidation have been shown to
occur and to influence fish acceptance.15–17
Before the freezing step is accomplished, adequate
storage techniques of fish material should be employed
to reduce post-capture losses Among the different
on-board handling systems that efficiently cool fish, the
most common one employed is chilling.18,19 During chilled storage of fish, important changes take place in the lipid fraction, leading to significant losses of sensory and nutritional values.20,21
The present study is related to the commercialisa-tion of frozen horse mackerel and aims to study the effect of previous chilled storage on the stability of horse mackerel lipids during frozen storage Chemical and sensory lipid damage indices were studied to assess rancidity development and, accordingly, to evaluate the shelf-life of this species under such conditions
MATERIALS AND METHODS Raw fish, sampling and processing
Fresh horse mackerel (T trachurus) were obtained 10 h after catching in June 2000 The length of the fish was
in the range 18–24 cm; the weight was in the range 250–280 g Upon arrival in the laboratory the fish were stored on ice in an isothermal room (0–2°C) Indi-vidual fish (120 pieces) were randomly distributed into three batches that were studied independently Horse mackerel from each batch (40 individual pieces) were taken for freezing after 0, 1, 3 and 5 days of chilled storage
Freezing was carried out at 80°C for 24h After
(Received 31 October 2001; revised version received 14 May 2002; accepted 5 August 2002)
* Correspondence to: Santiago P Aubourg, Instituto de Investigaciones Marinas (CSIC), Eduardo Cabello 6, E-36208 Vigo, Spain
E-mail: saubourg@iim.csic.es
Contract/grant sponsor: Co-operation Program (1999–2000) Germany–Spain (MCyT–INIA) of Agricultural Research
Contract/grant sponsor: Comisio´n Interministerial de Ciencia y Tecnologı´a; contract/grant number: ALI 99-0869
DOI: 10.1002/jsfa.1261
Trang 2that time, all fish samples were stored at 20°C.
Analysis of fish samples was undertaken on the white
muscle of fish material stored for 0, 1, 3, 5 and 7
months at 20°C
Composition analyses
Chemicals employed (solvents and reactants) were
reagent grade (E Merck, Darmstadt, Germany)
Water content was determined by weight difference
between the fresh homogenised muscle (1–2 g) and
after heating for 24 h at 105°C Results were
calcu-lated as g water per 100 g muscle
Lipids were extracted by the Bligh and Dyer22
method Results are expressed as g lipid per 100 g wet
muscle
Chemical lipid damage measurements
Free fatty acid (FFA) content was determined by the
Lowry and Tinsley23 method based on complex
formation with cupric acetate/pyridine Results are
expressed as g FFA per 100 g lipid Conjugated diene
(CD) formation was measured at 233 nm.24 Results
are expressed according to the formula CD = BV/w,
where B is the absorbance reading at 233 nm, V is the
volume (ml) and w is the mass (mg) of the lipid extract
measured The peroxide value (PV), expressed as meq
oxygen kg 1 lipid, was determined by the ferric
thio-cyanate method.25 The thiobarbituric acid index
(TBA-i) was determined according to Vyncke.26
Results are expressed as mg malondialdehyde kg 1
fish sample
Interaction compound formation
Interaction compounds formed between lipid
oxida-tion products and protein-like compounds were
investigated by measuring fluorescence formation
(Perkin-Elmer LS 3B) at 327/415 and 393/463 nm as
described in previous studies.27,28The relative
fluor-escence was calculated as RF = F/Fst, where F is the
fluorescence measured at each excitation/emission pair
and Fst is the fluorescence intensity of a quinine
sulphate solution (1mg ml 1 in 0.05MH2SO4) at the
corresponding wavelength The fluorescence ratio
calculated as FR = RF393/463 nm/RF327/415 nm was
studied in the aqueous phase resulting from lipid
extraction.22
Sensory analysis
Sensory analysis was conducted by a trained tasting
panel consisting of six to nine experienced judges For
each sample analysis, fillets of five fish were cooked in
plastic bags in a water bath Rancid odour and taste
were then evaluated on a scale from 0 (stage of no
rancidity at all) to 100 (stage where no increase in
rancidity is possible) Three categories were ranked:
good quality (0–29), fair quality (30–59) and
reject-able quality (60–100) Scores among panellists were
averaged
Statistical analyses
Data from the different chemical and sensory quality measurements were subjected to one-way ANOVA and correlation analysis (p < 0.05);29 comparison of means was performed using a least squares difference (LSD) method
RESULTS AND DISCUSSION
Water content ranged between 750 and 790 g kg 1 Lipid content ranged between 6.0 and 20.0 g kg 1 Differences in both constituents may be explained as a result of individual fish variation, and not arising from chilled or frozen storage; it is recommended to employ several individual fish for each sample to minimise this source of variation Comparison of the present results with previous research showed a higher water content for horse mackerel than for fattier fish species27and a lower water content for horse mackerel than for leaner fish species,30,31 in accordance with an inverse ratio between water and lipid matter.32
Lipid hydrolysis
In the present study the FFA content of the raw material (7.9 g kg 1) was similar to that of fatty fish species (tuna, sardine)27,33and lower than that of lean fish species (blue whiting, haddock, cod).30,31 As a result of frozen storage, significant (p < 0.05) differ-ences were only observed at month 3, where a sharp increase in the FFA content of all samples was found (Fig 1) For each frozen storage time, few significant (p < 0.05) differences could be observed among the four different chilling times studied, so that an effect of previous chilling time on hydrolysis during frozen storage could not be concluded
Lipid oxidation
Oxidised compounds as measured by CD formation (Fig 2) did not show a clear trend as a result of frozen storage, nor as a result of previous chilled storage Increases were found at month 5 in samples previously chilled for 0 and 1 day and also at month 7 in samples previously chilled for 0 and 3 days In the present study, CD detection did not prove to be sensitive for following changes arising from the chilling and freezing treatments employed; this index has been shown to be more accurate in the case of initial oxidation and model systems.34,35
Peroxide formation (Fig 3) showed a big increase at month 1 of frozen storage in all samples; thereafter, few significant increases were observed A strong effect
of chilled storage time on peroxide formation during frozen storage was observed During the whole frozen storage period, samples previously chilled for 3 and 5 days showed a higher PV than those previously chilled for 0 and 1 day, indicating a negative effect of the previous chilling treatment
Secondary oxidation as measured by TBA-i showed
a gradual general increase during frozen storage for all samples (Fig 4) A marked effect on carbonyl
com-Rancidity development in frozen horse mackerel
Trang 3pound formation during frozen storage was observed
for samples previously chilled for 3 and 5 days,
resulting in higher TBA-i values than those for
samples previously chilled for 0 and 1 day
Interaction compound formation
Few significant differences in fluorescence
develop-ment (FR) were observed among samples during the
first 3 months of frozen storage (Fig 5); thereafter a
significant (p < 0.05) increase was detected, which was
especially sharp at month 5 in samples previously
chilled for 5 days and at month 7 in samples previously
chilled for 3 and 5 days Increasing the length of chilled
storage time prior to freezing led to a slight increase in
the formation of fluorescent compounds
Formation of fluorescent products as a result of interactions between lipid oxidation compounds and nucleophilic molecules (proteins, peptides, etc) has been reported to be dependent on the formation of lipid oxidation products (peroxides and carbonyls) and also on temperature.36,37 In the present experi-ment, fluorescence formation developed faster in the later stages (5 and 7 months) of frozen storage, in accordance with increases in PV and TBA-i values (Figs 3 and 4).38,39
Sensory evaluation 40
Rancid odour showed an increase in all samples at month 3 (Fig 6) Thereafter a significant increase could only be assessed at month 7 in samples
previ-Figure 2 Conjugated diene (CD) formation in
frozen (0, 1, 3, 5 and 7 months) horse mackerel that
was previously chilled (0, 1, 3 and 5 days).
Figure 1 Free fatty acid (FFA) content in frozen (0,
1, 3, 5 and 7 months) horse mackerel that was
previously chilled (0, 1, 3 and 5 days).
Trang 4ously chilled for 3 and 5 days, indicating a negative
effect of previous chilling time on rancid odour
According to the categories assessed by the trained
panel, samples previously chilled for 3 and 5 days were
judged to be of fair quality at month 7 of frozen
storage; however, those previously chilled for 0 and
1 day were judged to be of good quality at month 7
Rancid taste increased at month 3 of frozen storage
(Fig 7) and continued to increase with frozen storage
time for most samples However, compared with most
samples, those previously chilled for 5 days scored
higher values After 7 months of frozen storage,
samples without chilling pre-treatment were found to
be of good quality, those previously chilled for 1 and 3
days were of fair quality and those previously chilled for 5 days were rejected
Correlation analyses
The different chemical and sensory analyses were tested for correlation with the previous chilled storage time at each frozen storage time (Table 1)
According to the results shown in Figs 1–5, PV and TBA-i were the only chemical indices that showed significant (p < 0.05) linear correlation values with the chilled storage time at all the frozen storage times tested PV showed, in all cases, correlation values higher than 0.84 Sensory analyses (odour and taste) also showed satisfactory correlations in most cases,
Figure 4 Thiobarbituric acid (TBA-i) values
obtained in frozen (0, 1, 3, 5 and 7 months)
horse mackerel that was previously chilled (0,
1, 3 and 5 days).
Figure 3 Peroxide (PV) formation in frozen (0,
1, 3, 5 and 7 months) horse mackerel that was
previously chilled (0, 1, 3 and 5 days).
Rancidity development in frozen horse mackerel
Trang 5according to Figs 6 and 7 In all cases, exponential and
logarithmic correlations were also tested; however, the
best results were obtained if linear correlations were
used
Correlation between the most reliable chemical
indices (PV and TBA-i) and the sensory assessments was also carried out (Table 2) According to Table 1, satisfactory correlation values were obtained for raw samples and also in cases of advanced oxidation degree (months 5 and 7)
Figure 5 Fluorescence (RF) formation in
frozen (0, 1, 3, 5 and 7 months) horse
mackerel that was previously chilled (0, 1, 3
and 5 days).
Figure 6 Changes in rancid odour value in frozen
(0, 1, 3, 5 and 7 months) horse mackerel that was
previously chilled (0, 1, 3 and 5 days).
Trang 6In accordance with previous research on lean8,31and
fatty15,27fish species, the present experiment showed
important hydrolytic and oxidative rancidity
develop-ment during frozen storage of horse mackerel This
lipid damage was assessed satisfactorily by traditional
chemical indices (FFA, PV, TBA-i and FR) and by
sensory analysis (rancid odour and taste) Indeed,
some chemical analyses (PV and TBA-i) showed
satisfactory correlations with sensory values and
proved to be reliable methods for assessing quality
changes (Tables 1 and 2)
Chilled storage time prior to frozen storage did not
provide a significant effect on hydrolytic rancidity
development (FFA formation) in the frozen product However, a negative effect on oxidative rancidity, according to chemical (PV, TBA-i and FR) and sensory (odour and taste) parameters, was observed for fish chilled for 3–5 days prior to frozen storage, leading to a significant quality loss in the frozen product
These results concur with previous studies on fattier species (frozen herring41–43 and canned sardine28,44) indicating a faster increase in oxidation product formation when pre-freezing chilled storage was extended
In the present study on the medium-fat-content species horse mackerel, satisfactory quality was main-tained up to 7 months of frozen storage provided that onboard fish handling was not longer than 3 days In cases where longer chilling pre-treatments are needed
Figure 7 Changes in rancid taste value in frozen
(0, 1, 3, 5 and 7 months) horse mackerel that was
previously chilled (0, 1, 3 and 5 days).
Table 1 Linear correlation values between lipid indices (chemical and
sensory) a
and previous chilling time calculated for each frozen storage time
Lipid index
Frozen storage time (months)
a
Abbreviations: FFA, free fatty acids; CD, conjugated dienes; PV, peroxide
value; TBA-i, thiobarbituric acid index; FR, fluorescence ratio.
* Significant at p < 0.05.
Table 2 Correlation values between sensory (odour and taste) and chemical
(PV and TBA-i) a
indices calculated for each frozen storage time Frozen storage time
(months) Odour (PV/TBA-i) Taste (PV/TBA-i)
a
Abbreviations as specified in Table 1.
* Significant at p < 0.05.
Rancidity development in frozen horse mackerel
Trang 7for further frozen horse mackerel commercialisation,
employment of chilling or frozen storage in
conjunc-tion with appropriate antioxidant treatment45,46 is
recommended to guarantee a longer shelf-life when
consumed as a frozen product
ACKNOWLEDGEMENTS
The authors thank Mr Marcos Trigo, Mrs Janet Ares
and Mrs Sybille So¨lter for technical assistance and are
grateful for the financial support provided by the
Co-operation Program (1999–2000) Germany–Spain
(MCyT–INIA) of Agricultural Research and the
Comisio´n Interministerial de Ciencia y Tecnologı´a
(project ALI 99-0869; 2000–2002)
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Rancidity development in frozen horse mackerel