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Colour stability of smoked muscle rainbow trout:
Packaging effect
A. Quiñones1, G. Choubert2*, R. Gómez1
SUMMARY
Colour and canthaxathin concentration changes were analysed in the mus- cle of smoked rainbow trout fed diets supplemented with canthaxathin (80 mg/kg of diet) in combination with three different lipid levels (6%, 16% and 24%). After the feeding period of 98 days fish were cold smoked and pro- cessed under three different packaging conditions: under air, under vacuum and under modified atmosphere. Smoke-curing lead to a decrease of L* and an increase of H(˚)ab more marked in fish fed the diet with high lipid level.
Modified atmosphere packaging lead to an increase of the product shelf-life as compared with air and vacuum packaging.
Key-words:
Trout, canthaxanthin, modified atmosphere, packaging.
RÉSUMÉ
Effet du conditionnement sur la stabilité de la couleur du muscle de truite arc-en-ciel.
Le changement de couleur et de concentration en canthaxathin a été suivi dans le muscle de truite arc-en-ciel ayant reçu un aliment contenant de la canthaxathin (80 mg/kg d’aliment) et trois différents taux de lipides alimen- taires (6 %, 16 % et 24 %). Après 98 jours d’alimentation, les poissons ont été fumés à froid et mis sous trois conditionnements différents : air, sous vide et atmosphère modifiée. Le fumage a entraîné une diminution de L* et une augmentation de H(˚)ab surtout chez les poissons recevant l’aliment contenant 24 % de lipides. Le conditionnement sous atmosphère modifiée a entraîné une augmentation de la durée de vie du produit comparé aux conditionnements sous air ou sous vide.
1. Departamento de Tecnología de los Alimentos, Facultad de Farmacia, Universidad del Pais Vasco (UPV), Vitoria, Spain.
2. Laboratoire de Nutrition des Poissons, Unité Mixte INRA-IFREMER, Saint Pée-sur-Nivelle, France.
*Correspondence: choubert@st-pee.inra.fr
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Mots clés :
Truite, canthaxathine, atmosphère modifiée, conditionnement.
INTRODUCTION
The red colour of the muscle of rainbow trout, due to carotenoids, is an important quality criteria for the fishfarmer and the consumer (CHOUBERT, 1982). This typical flesh colour needs to be maintained also during the proces- sing. Even smoked a damage in quality may occur (CIVERA et al., 1995). Smo- ked fish is a highly perishable product showing a short shelf-life. Packaging has many advantages, one of them being the preservation and the extension of the shelf-life (OKA, 1989). The objective of this experiment was to study colour and canthaxathin concentration changes in the muscle of smoked rainbow trout in relation with the use of three different packaging conditions: air, vacuum and modified atmosphere.
MATERIALS AND METHODS
One hundred and five rainbow trouts (Oncorhynchus mykiss) with a mean initial body weight of 200 g were fed three diets (Table 1) containing different lipid levels: 6% (Diet A), 16% (Diet B) and 24% (Diet C). Eighty mg of canthaxa- thin (Carophyll red®, F.Hoffman-La Roche, Basel, Switzerland)/kg of diet were added to the diets. Fish were hand fed ad libitum twice a day during 98 days at the INRA Experimental Fish Farm of Donzacq (Landes department, France).
After slaughtering fish were cold smoked (25˚C, during 3 h, at 65% relative humidity) at AZTI-SIO Technological Centre (Sukarrieta, Biscaya- Basque Country, Spain). Smoked fillets were packaged under air, under vacuum or under modified atmosphere (80% CO2 – 20% N2). The permeability characteris- tics of the plastic pouches (réf : BB305, Cryovac Sealed Air Corp., Barcelona, Spain) were as follows: for O2: 35 cm3/m2/24h at 23˚C, 50% relative humidity;
for CO2: 80 cm3/m2/24h at 23˚C, 50% relative humidity; for H2O: 10 g/m2/24h at 38˚C, 90% relative humidity. Samples were stored at +2ºC. Colour was ana- lysed using a spectrophoto-colorimeter (Mod. 805-i, Minolta ltd, Osaka, Japan).
Colour parameters L*, a* and b* were computer transformed into L*, C* and H(˚)ab according to WYSZECKI AND STILES (1967). Canthaxanthin concentra- tions of the fish muscle were measured with a spectrophotometer after extrac- tion (CHOUBERT, 1982).
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Table 1
Compositions (%) of the experimental diets.
Composition centésimale des aliments expérimentaux
RESULTS AND DISCUSSION
Before smoke-curing (Fig. 1) fish fillets from trout fed diet C showed colour parameters L* and H(˚)ab higher than those from trout fed diets A and B. These fillets displayed canthaxanthin concentrations higher than those from trout fed diet A and in a lesser extent diet B. This result suggests a dietary lipid level effect on the muscle fixation of canthaxathin which is a lipid soluble compound and corroborates the previous observations of NICKELL AND BROMAGE (1998) for astaxanthin in rainbow trout. After smoke-curing changes in the colour of fish fillets was noted especially a decrease of L* and an increase of H(˚)ab. This changes were significant (P<0.05) for fillets from trout fed the diet C. This obser- vation confirms our previous results (CHOUBERT et al, 1992).
Packaging effect on trout fillet colour lead to an increase of L*, the muscle becoming lighter, especially for fillets from trout fed the diet A and packaged under air. On the other hand there was an opposite tendency for fillets from trout fed diets B and C and packaged under vacuum. Moreover an increase in chroma (C*) was noted in fillets from trout fed diets A and B whatever the pac- kaging. For fillets from trout fed the diet C this increase was more marked. H(˚)ab was the parameter which was the most evolutive in fillets packaged under air.
This phenomenon was more marked for trout fed the diet with the highest lipid level (diet C). In return fillets packaged under modified atmosphere showed in the same time a low evolution. Fillets packaged under vacuum displayed inter- mediate values.
Ingredients1 Diet A Diet B Diet C
Fish meal 58.0 58.0 58.0
Gelatinised corn starch 13.5 16.0 20.0
Raw corn starch 24.0 13.0 0.0
Fish oil 1.5 10.0 19.0
Vitamin mix2 1.0 1.0 1.0
Mineral mix2 1.0 1.0 1.0
Sodium alginate 1.0 1.0 1.0
1. The feeds were steamless pelleted (Simon Heesen B.V., Boxtel, The Netherlands) through a 4-mm dye and stored at 4˚C for the duration of the experiment.
2. LABBE et al., 1993.
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Figure 1
Colour parameters evolution: lightness L* (A), chroma C* (B) and hue H(˚)ab (C) in trout fillets before ( ) and after smoke-curing ( ).
Évolution des paramètres de couleur : luminance L* (A), saturation C* (B) et teinte H(˚)ab (C) de filets de truite avant ( ) et après fumage ( ).
The packaging brought different effects on the canthaxanthin concentration of fish fillets (Fig. 2). A significant decrease (P<0.05) of the canthaxanthin con- centration was noted in smoked fillets packaged under air especially in those from fish fed the diet C (–55% in 28 days). On the other hand fillets from trout fed diets A and B showed a lower decrease (–24% and –31% respectively) during the same period of time. For fillets packaged under vacuum the decrease reached only 9%, 6% and 14% for fillets from trout fed diets A, B and C respectively. Any modification in the canthaxanthin concentration was observed after 28 days of storage for fillets from trout fed diets A, B or C. After
0 10 20 30 40 50
Lightness (L*)
Diet A Diet B Diet C
A
0 10 20 30
Chroma (C*)
Diet A Diet B Diet C
B
0 20 40 60
Hue (H°)ab
Diet A Diet B Diet C
C
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72 days of storage there was a small (–3,5%) decrease of the canthaxanthin concentration in fillets of trout fed the diet A with respect to those of fillets from trout fed diets B and C (–8,5%). Between the 72th and the 100th day of storage decreases in canthaxanthin concentrations reached 11%, 16% and 16,5% for fillets from trout fed diets A, B and C respectively with respect to initial canthaxanthin concentrations.
Figure 2
Canthaxathin content in smoked trout fillets (diet A ; diet B ; diet C )
packaged under air (A), under vacuum (B), under modified atmosphere (C) Contenu en canthaxathine de filets de truite fumés
(aliment A ; aliment B ; aliment C )
conditionnés sous air (A), sous vide (B), sous atmosphère modifiée (C)
A
0
0 8
0 8
0 8
2 4 6 8 10 12 14
14 28
Time (days)
Time (days)
Canthaxanthin (mg/kg)
B
0 2 4 6 8 10 12 14
14 28 42 56
Canthaxanthin (mg/kg)
C
0 2 4 6 8 10 12 14
14 28 42 56 72 100
Canthaxanthin (mg/kg)
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CONCLUSION
The use of modified atmosphere for the packaging of fillets from smoked trout lead to maintain the colour of the flesh and to save the canthaxanthin concentra- tion in a significant way in comparison with packaging under vacuum or under air.
The shelf-life extension may probably be due to the inhibitory effect on the bacte- rial growth of the gas mixture used in this experiment (CIVERA et al., 1995).
ACKNOWLEDGEMENTS
The authors acknowledge with thanks Y. Hontang, F. Sandres and F. Terrier for the maintenance of the experimental fish, Produits Roche (Neuilly-sur-Seine, France) for supplying canthaxanthin and Cryovac Sealed Air Corp. (Barcelona, Spain) for providing us with the plastic pouches (BB305). We also thank Irene Garcia and I. Goikoetxea of Azti-Sio Technological Centre (Sukarrieta, Spain) for their technical assistance in the smoking process. A.Q. was supported by fun- ding from the Department of Industry, Agriculture and fisheries of the Basque Government.
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