1
1
Improved Quality and Shelf Life of Farmed Trout
2
(Oncorhynchus mykiss) by Whole Processing in a Combined
3
Ozonised-Flow Ice Refrigeration System
4
5
Santiago P. Aubourg,a Silvia Testi,b Minia Sanxuás,c Carolina Gil,a and Jorge Barros-
6
Velázquez c,*
7
8
a
Department of Seafood Chemistry, Institute for Marine Research (IIM-CSIC), C/
9
Eduardo Cabello 6, E-36208 Vigo, Spain; b Department of Veterinary Morpho-
10
Physiology Sciences and Animal Production, University of Bologna, Italy; and cLHICA,
11
Department of Analytical Chemistry, Nutrition and Food Science, School of Veterinary
12
Sciences, University of Santiago de Compostela, E-27002 Lugo, Spain
13
14
Corresponding: Tel.:+34.600.942264; Fax:+34.982.252195; E-mail:
15
jorge.barros@usc.es
16
2
1
Abstract
2
3
Farmed trout (Oncorhynchus mykiss) is gaining an increasing importance in the
4
European markets because of its firm and flavourful flesh. With a view to extend its
5
shelf life, a combined refrigeration system consisting of ozone and flow ice previously
6
applied to to marine fish species, was evaluated for the sacrifice, cooling and chilled
7
storage of this fish species and compared to flow ice alone. Slaughter and chilled
8
storage of trout in the combined system slowed down microbial growth both at surface
9
and muscle levels, this inhibition reaching its maximum after 9 days of refrigerated
10
storage. Storage in ozonised flow ice also implied a significant inhibition of TMA-N
11
formation and slight reductions in the autolytic breakdown mechanisms, as determined
12
by the K value. Microbial and biochemical changes correlated well with respect to
13
sensory evaluation, which indicated a shelf life extension up to day 16 of storage for the
14
ozonised flow ice batch. This work opens the way to the practical application of
15
ozonised flow ice for the sacrifice, cooling and storage of continental fish species such
16
as farmed trout and others, due to the better maintenance of quality and the slight shelf
17
life extension provided as compared to flow ice alone.
18
19
Keywords: Flow ice, Ozone, Refrigeration, Trout, Slaughter, Shelf life, Fish Processing,
20
Chilled storage, Quality
21
Running title: Preservation of farmed trout in ozonised flow ice
22
3
1
1. Introduction
2
3
Flow ice –also known as slurry ice, fluid ice or liquid ice– is an advanced
4
refrigeration method for the sub-zero storage of fish and other food products. Flow ice
5
consists of a biphasic ice-water suspension that provides a remarkably high chilling rate
6
as compared to alternative and more traditional refrigeration systems like flake ice or
7
chilled water. Flow ice also prevents the physical damage suffered by seafood products
8
due to the spherical geometry of its microscopic particles, as compared with the
9
aciculate crystals of conventional flake ice. Flow ice can also be pumped, thus allowing
10
a more hygienic fish processing and process automation. (for a review: Piñeiro, Barros-
11
Velázquez, & Aubourg, 2004). In the recent years, sufficient scientific evidence has
12
confirmed the theoretical advantages of flow ice for the refrigeration of marine fish
13
specimens. Thus, since the pioneer works with finfish (Chapman, 1990) and albacore
14
(Price, Melvin, & Bell, 1991), to the more recent reports for turbot (Rodríguez, Barros-
15
Velázquez, Piñeiro, Gallardo, & Aubourg, 2006), sardine (Campos, Rodríguez, Losada,
16
Aubourg, & Barros-Velázquez, 2005; Losada, Barros-Velázquez, Gallardo, & Aubourg,
17
2004), horse mackerel (Rodríguez, Losada, Aubourg, & Barros-Velázquez, 2005), flow
18
ice systems have provided quality retention and shelf life extension in marine fish
19
species.
20
However, the present work was aimed at providing scientific data at three
21
different levels: (i) the convenience of not of the application of flow ice systems to
22
continental species such as trout, a fish species whose farming is making it more
23
available and more appreciated by European consumers; (ii) the usefulness of flow ice
24
systems for the whole processing of fresh fish material, this including slaughter, chilling
25
and refrigerated storage; (iii) finally, the benefits of the combination of flow ice and
4
1
ozone for the whole processing of farmed trout. Ozone has been traditionally used as a
2
disinfectant for fresh water aquaculture systems, and its applications for improving the
3
sensory quality and shelf life of fish have been described recently (Kötters et al., 1997;
4
Kim, Yousef, & Dave, 1999; Kim, Silva, Chamul, & Chen, 2000; Campos et al., 2005;
5
Rodríguez et al., 2006). The microbial identity of bacteria present in trout intestine has
6
been studied (Spanggaard et al., 2000): however, no quantitative information is
7
currently available about the microbial activity in trout muscle as affected by different
8
preservation techniques.
9
Accordingly, in this work we evaluated the potential application of an integral
10
slaughter, chilling and storage refrigeration system –resulting from the combination of
11
ozone and flow ice– to farmed trout. The evaluation of the effects of flow ice systems
12
on the quality of trout was carried out by biochemical, sensory and microbial analysis.
13
14
2. Materials and methods
15
16
2.1. Refrigeration systems
17
Flow ice (FI) was prepared using a FLO-ICE prototype (Kinarca S.A.U., Vigo,
18
Spain). The composition of the FI binary mixture was 40% ice and 60% water, prepared
19
from filtered seawater (salinity: 3.3%). The temperature of the FI mixture was -1.5ºC.
20
When required, the injection of ozone in the FI mixture was accomplished with a
21
prototype provided by Cosemar Ozono (Madrid, Spain), the redox potential being
22
adjusted to 700 mV (0.20 mg ozone/l). In this batch, the ozone concentration was
23
constantly monitored by checking the redox potential in the liquid phase.
5
1
2.2. Fish material and sampling protocol
2
Specimens (108 individuals) of rainbow trout (Oncorhynchus mykiss) (weight
3
range: 0.23-0.33 kg; length range: 25-30 cm) were obtained from an aquaculture facility
4
(Isidro de la Cal, La Coruna, Spain) and were sacrificed at the farm by immersion for at
5
least 20 min in either flow ice (FI: 54 individuals) or ozonised flow ice (OFI: 54
6
individuals). The fish specimens were not headed nor gutted. In both systems, fish were
7
surrounded by FI or OFI at a 1:1 fish-to-ice ratio and transported during 2 h at 0ºC to
8
the laboratory. Then, the fish specimens were maintained in their corresponding icing
9
medium and directly placed in an isothermal room at +1ºC. On day 1, nine specimens
10
from each batch were taken for analysis and divided into three groups (three individuals
11
in each group) that were studied separately (n = 3). Once fish specimens had been
12
subjected to sensory analyses, the white muscle was aseptically dissected and used for
13
microbial and biochemical analyses. Fish sampling was performed on days 1, 3, 6, 9, 13
14
and 16 of refrigerated storage, according to the same sampling design (n = 3).
15
16
2.3. Sensory analysis
17
Sensory analyses were conducted in whole fish by a panel consisting of five
18
experienced judges, according to official guidelines (Table 1) concerning fresh and
19
refrigerated fish (Council Regulation, 1990). Four categories were ranked: highest
20
quality (E), good quality (A), fair quality (B), and unacceptable quality (C). The
21
panellists included in this study had been involved in sensory analysis of different fish
22
species during ten years. Previously to the present experiment, the panellists were
23
specially trained with chilled rainbow trout. Sensory assessment of the fish included the
24
examination of the following parameters: skin, eyes, external odour, gills, consistency
6
1
and flesh odour. At each sampling time, the fish specimens were presented to panellists
2
and were scored individually. The panel members shared samples tested.
3
4
2.4. Microbiological analyses
5
Fish skin sections of 5 cm2 were swabbed with sterile 0.1% peptone water
6
(Oxoid Ltd., London, UK) and the microbial load was resuspended in 10 ml of 0.1%
7
peptone water. Samples of 5 g of fish muscle were also dissected aseptically in parallel
8
from skinned chilled specimens, mixed with 45 ml of 0.1% peptone water, and
9
homogenised in a stomacher (Seward Medical, London, UK). In both cases, serial
10
dilutions from the skin or muscle microbial extracts were prepared in 0.1% peptone
11
water. Total aerobic and psychrotrophic bacteria from surface and muscle trout samples
12
were investigated in Plate Count Agar (PCA, Oxoid) after incubation at 30C for 48 h
13
or at 7-8C for 10 days, respectively, as described elsewhere (Ben-Gigirey, Vieites
14
Baptista de Sousa, Villa, & Barros-Velázquez, 1998; Rodríguez, Losada, Aubourg, &
15
Barros-Velázquez, 2004). Microorganisms exhibiting a proteolytic phenotype were
16
investigated in casein-agar medium as previously described (Phaff, Starmer, Lachance,
17
& Ganter, 1994)
18
19
2.5. Chemical analyses
20
Analysis of the nucleotide autolytic degradation rate was carried out by HPLC as
21
described elsewhere (Ryder, 1985). The K value was calculated according to the
22
following concentration ratio: K value = 100 x (hypoxanthine + inosine) / (adenosine
23
triphosphate + adenosine diphosphate + adenosine monophosphate + inosine
7
1
monophosphate + inosine + hypoxanthine). Total volatile base-nitrogen (TVB-N)
2
contents were measured as described elsewhere (Aubourg, Sotelo, & Gallardo, 1997).
3
Briefly, fish muscle (10 g) was extracted with 6% perchloric acid and brought up to 50
4
ml. TVB-N contents were determined, after steam-distillation of the acid extracts
5
rendered alkaline to pH 13 with 20% NaOH, by titration of the distillate with 10 mM
6
HCl. The results were expressed as mg TVB-N/100 g muscle. Trimethylamine-nitrogen
7
(TMA-N) values were determined by the picrate method, as previously described
8
(Tozawa, Erokibara, & Amano, 1971). This involves the preparation of a 5%
9
trichloroacetic acid extract of fish muscle (10 g/25 ml). Results were expressed as mg
10
TMA-N/100 g muscle.
11
The lipid fraction was extracted using the Bligh & Dyer method (1959). Lipid
12
oxidation was assessed by the thiobarbituric acid index (TBA-i), which was determined
13
according to Vyncke (1970). Results were expressed as mg malondialdehyde/Kg fish
14
sample. The free fatty acid (FFA) content was determined by the Lowry and Tinsley
15
method, based on complex formation with cupric acetate-pyridine (Lowry & Tinsley,
16
1976). The results were expressed as g FFA/100 g lipids.
17
18
2.6. Statistical analyses
19
A multivariate analysis was performed to study the effect of each refrigeration
20
system on the microbiological and chemical parameters. One-way analysis of variance
21
(ANOVA) was also used to explore the significance of differences among
22
microbiological and chemical parameters throughout storage for each refrigeration
23
system. Multiple comparisons between parameters were carried out by the DMS test.
8
1
All tests were carried out using the SPSS software (SPSS Inc., Chicago, IL). A
2
confidence interval at the 95% level (p<0.05) was considered in all cases.
3
4
3. Results and discussion
5
6
3.1. Sensory analyses
7
The results of the sensory analyses are shown in Table 2. It can be observed that
8
trout specimens processed in the combined system of flow ice and ozone retained a
9
good quality (E or A categories) up to day 13, except for the gills aspect. However,
10
when the flow ice was used alone, such good quality was retained only for up to day 6
11
(Table 2). It is remarkable that the limiting factor of sensory acceptability in the flow ice
12
batch was the external odour, which caused the rejection of the flow ice batch on day
13
16. Previous works carried out at our laboratory indicated that continental trout
14
specimens of similar sizes as those studied in this work exhibit an average shelf-life of
15
13 days, this being in agreement with the results obtained for the flow ice batch.
16
Accordingly, the combined use of flow ice and ozone may slightly increase from 13 to
17
16 days the shelf life of continental trout according to the sensory evaluation.
18
Previous studies have reported that the application of ozone extends the shelf life
19
of rockfish (Sebastes spp.) (Kötters et al., 1997), and catfish (Ictalurus punctatus) fillets
20
(Kim et al., 2000). Other authors have also reported reductions in the discoloration rate
21
of minced horse mackerel as a benefit of washing with ozonised water (Chen, Chiu, &
22
Huang, 1997), and a better maintenance of the sensory quality of scad (Trachurus
23
trachurus) treated on-board with gaseous ozone (Da Silva, Gibbs, & Kirby, 1998).
24
Likewise, a previous study performed at our laboratory represented the first report of the
9
1
monitored application of ozone in the liquid phase of a subzero biphasic ice-water
2
mixture for the storage of a marine fish species such as turbot (Psetta maxima)
3
(Rodríguez et al., 2006). The present study provides evidence for the first time of the
4
usefulness of the combination of ozone and flow ice for the extension of shelf-life of a
5
continental fish species such as trout.
6
7
3.2. Microbiological analyses
8
Microbial development in trout muscle throughout chilled storage is displayed in
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Table 3. The use of flow ice alone (FI batch) revealed as an accurate processing strategy
10
for the slaughter, chilling and refrigerated storage of trout. Thus, the results compiled in
11
Table 3 for such batch clearly indicated a slow microbial growth in trout muscle
12
according to the three microbial parameters tested. It is remarkable that the microbial
13
numbers were below 3 log CFU/g even until day 9 of storage, a result that correlated
14
well with the sensory quality investigated in parallel (Table 2). Significant (p<0.05)
15
increments in the microbial numbers were observed at advanced storage periods (day 13
16
and onwards, Table 3). However, even after 16 days of storage, the microbial counts in
17
the FI batch did not reach concentrations of 6 log CFU/g, these numbers being below
18
those considered as necessary to induce fish spoilage (Gram & Huss, 1996). These
19
results clearly indicate that the rapid chilling conditions provided by the FI mixture
20
together with its hygienic handling, provided a good microbial control of refrigerated
21
trout.
22
With respect to the evaluation of the whole processing of trout in ozonised flow
23
ice (OFI batch), this system led to average lower counts for aerobic mesophiles,
24
psycrotrophic and proteolytic bacteria in trout muscle, as compared to the FI batch
25
(Table 3). Thus, statistical analyses revealed significant (p<0.05) differences between FI
10
1
and OFI batches for the aerobic mesophiles (storage days 3, 9 and 13), psychrotrophes
2
(storage days 3, 6, 9 and 13) and proteolytic bacteria (storage days 6, 9 and 13) (Table
3
3). Thus, the microbial growth was slower in the OFI batch as compared to the FI batch,
4
the numbers being below 4 log CFU/g even after 13 days of storage. Considering the
5
whole storage period of 16 days, the average differences between batches were 0.42 log
6
CFU/g, 0.44 log CFU/g and 0.46 log CFU/g units for the aerobes, psychrotrophes and
7
proteolytic bacteria, respectively.
8
The assessment of microbial growth on trout skin along chilled storage is shown
9
in Table 4. Two microbial groups were investigated at this phase: mesophilic and
10
psychrotrophic bacteria. The microbial populations increased with storage time in both
11
batches but the counts were below 4 log CFU/cm2 even after 16 days of storage, this
12
indicating a very limited microbial growth at surface level. The surface washing of trout
13
skin caused by flow ice could be a possible explanation for the low surface numbers
14
determined in this continental fish species, as it has been described for marine fish
15
species (Rodríguez et al., 2005; Campos et al., 2005; Rodríguez et al., 2006). However,
16
the combined use of ozone and flow ice (OFI batch) exerted an additional reduction
17
effect on the microbial numbers after 3 days of storage (Table 4). Considering the whole
18
storage period of 16 days, the average differences between batches were 0.20 log CFU/g
19
and 0.26 log CFU/g for the aerobes and psychrotrophes, respectively. Remarkably,
20
statistically-significant (p<0.05) differences between batches for at least one of the
21
microbial groups investigated were observed at days 6, 9 and 13 of refrigerated storage
22
(Table 4).
23
The ability of ozone to inactivate food surfaces has been subject of discussion.
24
Some authors have previously reported that ozone decreases the surface microbial load
25
of fish during its chilled storage (Dondo, Nachtman, Doglione, Rosso, & Genetti, 1992;
11
1
Da Silva, Gibbs, & Kirby, 1998). On contrast, other authors have suggested that ozone
2
inactivates bacteria less effectively when they are attached to solid surfaces as compared
3
to low ozone-demand liquid media (Kim, Yousef, & Dave, 1999). The results obtained
4
in our study indicated a slight reduction of the microbial populations present on the
5
surface of trout due to ozone, this supporting the former statement. The results of
6
microbial analyses of trout stored in OFI also correlated well with sensory analysis, the
7
latter indicating a slightly better quality maintenance in the OFI batch as compared to
8
the FI batch (Table 2). According to our results, it can be concluded that the combined
9
use of flow ice and ozone for the slaughter, chilling and storage of continental trout
10
provides and additional advantage at the microbial level, as determined by the microbial
11
numbers present in the fish skin and flesh along 16 days of storage. Although microbial
12
growth was significantly slowed down at certain storage periods in the OFI batch, none
13
of the microbial groups investigated reached counts higher than 106 CFU/g, also
14
indicating that microbial spoilage alone does not represent the limiting factor to the
15
shelf life of continental trout.
16
17
3.3. Chemical analyses
18
The chemical parameters investigated in trout muscle along storage are shown in
19
Table 5. With respect to the nucleotide autolytic degradation rate, the K value increased
20
to values above 80 after 9 days of storage in both baches. Remarkably, no significant
21
(p>0.05) difference was observed between the ozonised and the non-ozonised flow ice
22
batches except for day 13, in which a lower K value was determined in the OFI batch.
23
As a consequence of this, no remarkable inhibitory effect of ozone on the autolytic
24
degradation pathway could be assessed.
12
1
The formation of TVB-N was assessed in both batches, no significant (p>0.05)
2
difference being observed between both storage systems. Moreover, the evolution of
3
TVB-N concentrations along storage in any of the storage systems tested neither
4
revealed significant variation, such concentrations being in all cases below 25 mg/100 g
5
muscle even after 16 days of storage (Table 5). These results suggest that TVB-N,
6
which is a widely considered parameter to assess quality evolution of marine fish
7
species, is not useful as a quality indicator of trout quality. Thus, even when sensory
8
analysis indicated unacceptable quality, the levels of TVB-N were not significantly
9
(p>0.05) different than the initial (Table 5).
10
On contrast to TVB-N, the evolution of TMA-N content in both batches
11
provided significant (p<0.05) differences between batches (Table 5). Thus, on day 6 and
12
onwards statistically-significant (p<0.05) differences in the TMA-N content were
13
observed between FI and OFI batches. Remarkably, on day 13 the TMA-N content of
14
the FI batch nearly duplicated that determined in the OFI batch. These results suggest
15
that the incorporation of ozone in the OFI batch significantly reduces the growth of
16
TMA-producing bacteria, this representing a practical advantage with respect to the use
17
of FI alone. It is also remarkable that TMA-N evolution in both batches correlated well
18
with the results of sensory analysis. Nevertheless, it should be highlighted that TMA-N
19
levels in both trout batches were in all cases much lower than those described for other
20
small and medium-sized marine fish species, in which sharp increases in the TMA-N
21
content were noticed after 9-12 days of storage in flake ice (Pérez-Villarreal & Pozo,
22
1990; Fernández-Salguero & Mackie, 1987; Ruíz-Capillas & Moral, 2001; Baixas-
23
Nogueras, Bover-Cid, Veciana-Nogués, & Vidal-Carou, 2002). Such a different
24
behaviour was expected, since our study was focused on a continental fish species such
13
1
as trout which OTMA content is necessarily much lower than those normally found in
2
marine fish species.
3
Lipid hydrolysis was determined according to FFA assessment. Significant
4
(p<0.05) increases in the formation of FFA along storage time were observed in both
5
batches during the first 3 days (Table 5). After that sampling time, only slight increases
6
in this parameter were observed, this indicating that lipid hydrolysis events are low in
7
continental trout. Accordingly, no significant (p>0.05) effect of ozone on lipid
8
hydrolysis was concluded, this indicating a similar protection of trout muscle against
9
lipid hydrolysis in both batches. Although the release of FFA itself does not imply
10
significant nutritional loss of quality, its accumulation has been linked to lipid oxidation
11
enhancement (Miyashita & Takagi, 1986; Yoshida, Kondo, & Kajimoto, 1992) and to
12
texture deterioration due to interaction between FFA and proteins (Mackie, 1993;
13
Sikorski & Kolakowska, 1994). Interestingly, according to the results obtained in our
14
study the combination of ozone and flow ice did not imply any significant enhancement
15
of lipid damage in trout muscle.
16
Lipid oxidation was followed by the TBA-i in order to evaluate if the presence
17
of ozone might imply any drawback at this level. As for FFA, statistically-significant
18
(p<0.05) increases in this index along storage time were observed in both batches until
19
day 3 (Table 5). After that sampling time, the TBA-i only increased slightly, reaching
20
final values below 0.25 mg/Kg in both batches. Remarkably, the presence of ozone in
21
the OFI batch did not increase significantly (p<0.05) the formation of TBA-reactive
22
substances, this underlining that this antimicrobial agent may provide an added value in
23
the control of microbial spoilage in continental trout without causing any significant
24
(p<0.05) enhancement of lipid oxidation mechanisms.
25
14
1
4. Conclusions
2
3
Unlike marine fish species, little information about the usefulness of flow ice
4
sub-zero storage systems in continental fish species is currently available. In this study,
5
a combined system composed of ozone and flow ice has been evaluated in parallel to
6
flow ice for the whole processing of continental trout, this including its slaughter,
7
cooling and storage. The better sensory quality maintenance of the OFI batch was in
8
agreement with the better microbial control, both at skin and muscle levels, and the
9
slight reduction of TMA-N formation. On the basis of the results obtained, the
10
combined use of ozone and flow ice is advisable for the hygienic processing of farmed
11
trout and other continental fish species.
12
13
Acknowledgements
14
This work was supported by a project granted by the Dirección Xeral de I+D
15
from the Galician Government (Xunta de Galicia, Project PGIDT05TAL00701CT). The
16
authors also wish to thank KINARCA S.A.U. (Vigo, Spain) for providing the flow ice
17
equipment, and CoseMar Ozono (Madrid, Spain) for providing the ozone generator.
18
19
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20
1
TABLE 1
2
3
Scale employed for evaluating the sensory quality of trout batches
Attribute
Skin
Highest quality
Good quality
Fair quality
Unacceptable
(E)
(A)
(B)
(C)
Very intense
Milky mucus;
Slightly greyish
Widely opaque
pigmentation;
insignificant
mucus;
mucus;
transparent mucus
pigmentation
pigmentation
important
losses
without shine
pigmentation
losses
External odour
Sharply seaweedy
Weakly
Incipiently sour
and shellfish
seaweedy and
and putrid
Sour and putrid
shellfish
Gills
Consistency
Brightly red;
Rose colored;
Slightly pale;
Grey-yellowish
without odor;
without odor;
incipient fishy
color; intense
lamina perfectly
lamina adhered
odor; lamina
ammonia odor;
separated
in groups
adhered in
lamina totally
groups
adhered
Presence or partial
Firm and elastic;
Presence of
Important shape
disappearance of
pressure signs
mechanical
changes due to
rigor mortis
disappear
signs; elasticity
mechanical
symptoms
immediately and notably reduced
factors
completely
Flesh odour
Sharply seaweedy
Weakly
Incipiently sour
and shellfish
seaweedy and
and putrid
shellfish
4
5
Sour and putrid
21
1
TABLE 2
2
3
Comparative sensory evaluation of trout stored in batches
Storage time (days)
1
3
6
9
13
16
FI
OFI
FI
OFI
FI
OFI
FI
OFI
FI
OFI
FI
OFI
Skin
E
E
E
E
A
E
B
A
B
A
B
B
Eyes
E
E
E
E
E
E
A
A
B
A
B
B
External
E
E
E
E
E
E
A
A
B
A
C
B
Gills
E
E
E
E
A
A
B
B
B
B
B
B
Consistency
E
E
A
A
A
A
A
A
A
A
B
B
Flesh odour
E
E
E
E
E
E
A
A
A
A
A
A
odour
4
5
22
1
TABLE 3
2
3
Comparative microbial growth in trout muscle stored in flow ice (FI) or ozonised
4
flow ice (OFI)
Storage
time
(days)
5
6
7
Aerobic mesophiles
(log CFU/g)
Psychrotrophes
(log CFU/g)
Proteolytic bacteria
(log CFU/g)
FI
OFI
FI
OFI
FI
1
1.62 a
1.61 a
1.10 a
1.00 a
2.32 a
(0.33)
(0.37)
(0.15)
(0.00)
(0.47)
3
2.45 a
2.08 b
2.19 a
1.33 b
2.83 a
(0.13)
(0.17)
(0.37)
(0.30)
(0.65)
6
1.94 a
1.83 a
2.54 a
1.79 b
2.48 a
(0.34)
(0.04)
(0.35)
(0.29)
(0.32)
9
2.67 a
1.78 b
1.67 a
1.10 b
2.67 a
(0.26)
(0.25)
(0.14)
(0.15)
(0.25)
13
4.42 a
3.48 b
4.24 a
3.82 b
4.21 a
(0.27)
(0.35)
(0.15)
(0.11)
(0.35)
16
5.91 a
5.76 a
5.64 a
5.74 a
5.87 a
(0.80)
(0.60)
(0.80)
(0.50)
(0.13)
Results are average values and standard deviations (between brackets)
Results followed by different letters are statistically different (p<0.05)
OFI
1.99 a
(0.00)
2.64 a
(0.66)
1.98 b
(0.00)
2.15 b
(0.15)
3.25 b
(0.32)
5.65 a
(0.56)
23
1
TABLE 4
2
3
Comparative microbial growth in trout surface stored in
4
flow ice (FI) or ozonised flow ice (OFI)
Storage
time
(days)
5
6
Aerobic mesophiles
(log CFU/cm2)
Psychrotrophes
(log CFU/cm2)
FI
OFI
FI
OFI
1
0.10 a
0.64 a
0.10 a
0.55 a
(0.01)
(0.05)
(0.05)
(0.10)
3
1.49 a
1.44 a
0.10 a
0.10 a
(0.23)
(0.16)
(0.02)
(0.05)
6
1.71 a
0.74 b
0.30 a
0.26 a
(0.24)
(0.08)
(0.20)
(0.12)
9
0.71 a
0.59 a
1.74 a
0.23 b
(0.16)
(0.15)
(0.25)
(0.10)
13
2.53 a
2.15 b
3.13 a
2.59 b
(0.18)
(0.14)
(0.30)
(0.12)
16
3.56 a
3.32 a
3.87 a
3.97 a
(0.30)
(0.15)
(0.40)
(0.35)
Results are average values and standard deviations (between brackets)
Results followed by different letters are statistically different (p<0.05)
24
1
TABLE 5
2
3
Comparative evolution of biochemical quality in trout muscle stored in flow ice (FI) or ozonised flow ice (OFI)
Time
TVB-N
TMA-N
FFA
TBA-i
(days)
FI
OFI
FI
OFI
FI
OFI
FI
OFI
FI
OFI
1
16.76 a
24.99 b
23.68 a
24.43 a
0.020 a
0.031 b
0.18 a
0.19 a
0.15 a
0.24 a
(2.81)
(6.69)
(0.61)
(0.95)
(0005)
(0.015)
(0.04)
(0.07)
(0.05)
(0.06)
45.37 a
43.96 a
23.05 a
21.92 a
0.036 a
0.036 a
0.56 a
0.59 a
0.23 a
0.37 b
(7.62)
(7.06)
(1.83)
(1.32)
(0.003)
(0.007)
(0.16)
(0.16)
(0.05)
(0.05)
70.61 a
64.58 a
23.61 a
23.83 a
0.074 a
0.051 a
0.55 a
0.57 a
0.34 a
0.34 a
(3.47)
(8.41)
(0.22)
(0.68)
(0.037)
(0.013)
(0.15)
(0.24)
(0.14)
(0.03)
84.08 a
81.16 a
22.91 a
21.95 a
0.073 a
0.047 b
0.55 a
0.64 a
0.23 a
0.15 a
(5.37)
(1.30)
(1.48)
(0.70)
(0.006)
(0.014)
(0.01)
(0.11)
(0.08)
(0.05)
87.94 a
74.91 b
23.28 a
23.60 a
0.142 a
0.072 b
0.54 a
0.71 a
0.18 a
0.24 a
(1.43)
(3.19)
(2.62)
(1.42)
(0.036)
(0.027)
(0.19)
(0.12)
(0.04)
(0.08)
87.03 a
90.34 a
23.33 a
22.16 a
0.222 a
0.169 b
0.61 a
0.70 a
0.20 a
0.24 a
(3.15
(2.71)
(1.53)
(0.94)
(0.030)
(0.029)
(0.08)
(0.09)
(0.02)
(0.05)
3
6
9
13
16
4
5
K value
Results are average values and standard deviations (between brackets)
Results followed by different letters are statistically different (p<0.05)