Effect of Blood Removal Protocol and Superchilling on Quality Parameters of Prerigor Filleted Farmed Atlantic Cod (Gadus morhua) Bjørn Tore Rotabakk, Hogne Bleie, Lars Helge Stien, and Bjorn Roth
A total of 40 farmed Atlantic cod (Gadus morhua) were in 2 groups either fillet directly after stunning and spray washed or produced into fillets according to traditional slaughter methods including exsanguination for 30 min, gutting and washing. Both groups were either stored superchilled or traditionally on ice. After 7 d postmortem color (CIE L∗ , a∗ , b∗ ) and fillet shrinkage was measured by computer imaging along with drip loss and texture hardness. Results show that superchilled fillets had significant lower core temperature than fillets stored on ice during the entire 7 d storage period. This resulted in reduced fillet shrinkage from 14.7% to 6.9% and less drip loss dropping from 9.45% to 3.99% in average. Processing the fish directly into fillets resulted in satisfactory blood drainage, where all groups were in particularly well exsanguinated with a∗ values below zero. No color difference was observed between filleting groups or chilling methods. Spray washing of the fillets resulted in water uptake and higher drip loss in interaction with chilling method. We conclude that filleting farmed fish in one step is feasible.
Keywords: farmed cod, novel process, prerigor, quality, superchilling
Traditionally farmed fish are slaughtered and processed over several steps, which often include live chilling, stunning, exsanguination, chilling, gutting, rinsing, decapitation, filleting before the fillets are packed into polystyrene boxes and shipped with ice. These processes are often time, laboring, space, and energy consuming. A novel processing line for filleting of farmed fish is gutting and filleting the fish directly after decapitation and replacing exsanguination with spray washing the fillets. In addition, all the cooling steps are replaced by superchilling the fillets. This novel process line gives fillets with comparable if not superior quality compared to the traditional process.
Practical Application:
Introduction Traditionally farmed fish such as Atlantic salmon (Salmo salar) and Atlantic cod (Gadus morhua) are slaughtered and processed over several steps, which often include live chilling, stunning, exsanguination, chilling, gutting, rinsing, decapitation, filleting before the fillets are packed into polystyrene boxes and shipped with ice. These processes are often time, laboring, space, and energy consuming, as the fish are placed into large refrigerated sea water tanks for chilling, exsanguination, and washing between each step that requires manually handling of fish into machines. Basically many of these steps are considered as suboptimal for industrialized processing for farmed fish. For exsanguination, previous studies have shown that timing is most important, not the way exsanguination is performed, where major veins must be cut (Robb and others 2003). This means that instead of exsanguination, the fish can be directly gutted (Roth and others 2009b). For Atlantic cod, direct gutting has shown to cause higher redness of the flesh (Digre and others 2011b), but the question rises whether the carcass were properly washed, which is crucial for blood removal of the muscle (Roth and others 2009b). In order to remove blood from the fillet, early filleting MS 20131732 Submitted 11/21/2013, Accepted 2/17/2014. Authors Rotabakk and Roth are with Nofima AS, Processing Technology Dept., Box 8034, N-4068 ˚ Stavanger, Norway. Author Bleie is with Atlantic cod farms AS, N-6005 Alesund, Norway. Author Stien is with Inst. of Marine Research, N-5392 Storebø, Norway. Direct inquiries to author Rotabakk (E-mail: [email protected]).
R C 2014 Institute of Food Technologists
doi: 10.1111/1750-3841.12437 Further reproduction without permission is prohibited
in combination with washing and gravity is the major mechanism for removing blood from the muscle, where prerigor filleted fillets had 5 folds less blood than postrigor filleted fish (Roth and others 2009b). This means that most of the blood will follow the carcass, while the little blood that remains in the muscle will be cleaned out quickly when prerigor filleted. Superchilling is an emerging technique that maintains food quality and safety while retaining food at a higher temperature than “normal” for frozen storage, at temperature around the initial freezing point of the food, typical around –1 °C for cod (Simpson and Haard 1987). Generally, the shelf life of superchilled food is extended compared to traditionally chilled foods, primarily because of decreased autolytic and microbiological activity at the subzero temperatures (Haard 1993). Correspondingly, the sensory quality has proven to be increased that of fresh cod (Olafsdottir and others 2006), and increased bacterial quality (Olafsdottir and others 2006; Duun and Rustad 2007), hence increased shelf life. Superchilling represents a technology that can greatly reduce the need for ice during chilled transport, enabling efficient transport and decreased emission in the packaging and distribution processes (Vold and Hanssen 2010). For fish that are filleted postrigor, the muscle is still attached to the skeleton when it undergoes rigor mortis. Consequently, the postrigor fillet will be less exposed to shrinkage in longitudinal direction than fish being filleted prerigor, but may instead lead to increased amount of fillet gaping. When fish are filleted prerigor, the muscle is free to contract and therefore undergoes shortening and the thickness of the fillet increases (Stien and others 2006; Vol. 79, Nr. 5, 2014 r Journal of Food Science E881
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Abstract:
Direct filleting and superchilling . . .
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Jørpeland and others 2013). Premortem stress and temperature is know to affect postmortem processes such as drip loss (DL), muscle contraction speed and degree of muscle shortening (Stien and others 2005; Jørpeland and others 2013). How superchilled prerigor fillets from Atlantic cod will act during rigor is still not investigated. One futuristic scenario for industrialized slaughter of fish would be to skip all steps and instead, immediately after stunning, decapitate the animal and fillet the carcass directly, before spray rinsing and concentrate all energy on chilling the fillets by superchilling. The aim of this study was therefore to investigate the effect of direct filleting and superchilling on blood removal of the muscles, color, muscle shortening, and water loss.
as a cooling media. The freezer was preset on –60 °C, and the processing time was set to 4 min. Before transport, the 4 groups were packaged in traditional expanded polystyrene boxes. Approximately 12 kg of fillets were packaged in each box, and 3 kg of ice was added in the boxes with traditionally iced fillets, according to the design. All the boxes were transported and stored under chilled conditions (approximately 0.5 °C). The fillets were under transport for 48 h and stored for additional 5 d, 7 d in total, before quality analysis. During storage, ice was added to secure excess ice, while the superchilled fillets remained unopened. In each box, the temperature of one fillet in the middle was logged every 10 min by a wireless logger (Dickson HT120, Dickson, Ill., U.S.A.).
Materials and Methods
Color Fillet surface color (CIE Lab) was assessed on all the fillets in the design (n = 80) by a digital photo imaging color-measuring system (DigiEye full system, VeriVide Ltd., Leicester, UK) after 7 d of storage. The fillets were placed in a standardized lightbox with daylight (6400 K) and photographed with a calibrated digital camera (Nikon D80, 35 mm lens, Nikon Corp., Japan). The pictures were analyzed with DigiPix software (VeriVide Ltd.) and the color quantified as an average for the whole fillet surface. L∗ describes the products lightness (L∗ = 100 = white, and L∗ = 0 = black), a∗ describes the intensity of color on the red– green axis (a∗ > 0 = red, and a∗ < 0 = green) and b∗ the intensity of color on the yellow–blue axis (b∗ > 0 = yellow, and b∗ < 0 = blue). In addition, whiteness was calculated according to Park (1994):
Raw material The experiment was carried out on 40 marked sized (2 to 4 kg) farmed Atlantic cod (Gadus morhua L.) from the North-West coast of Norway in November 2009, giving a total of 80 fillets (620 ± 146 g). All fish were starved for 2 wk before well-boat transport and rested for 2 d in sea cages before slaughter. At slaughter, the temperature in the sea was 6.5 °C. Design A full factorial design with 2 factors (blood removal protocol and chilling method) was set up. “Blood removal protocol” contained 2 variants: direct filleted and traditional and “chilling method” contained 2 variants: superchilling and traditional icing. This provided in total 4 variants with 20 fillets in each group. In addition, the left fillet of a fish was submitted to superchilling, while the right fillet was ice stored. The control was the fillets of traditionally exsanguinationed fish combined with traditional iced storage. After 7 d in expanded polystyrene boxes, the fillets were assessed for DL, shrinkage, color, and texture. Blood removal and filleting Prior to the experiment, rested fish were carefully crowded at one end of the cage (200 kg/m3 ). One fish at the time was sampled with a dip net and immediately killed by a sharp blow to the head. One group of fish (Traditional) was prerigor filleted according to traditional procedures: gill cut, followed by 30 min exsanguination in chilled seawater, then gutting, washing (tank for 15 min), decapitation, filleting and skinning. The other experimental group (Direct filleted) was immediately after killing decapitated, filleted, skinned and spray washed (10 min). For both groups, the fish were manually decapitated and gutted. The Baader 252 and Baader 51 (Baader Inc., Germany) were used for filleting and skinning, respectively. Spraywashing was conducted by manually sprinkling groups of five fillets with 4 °C fresh water using a hose with a nozzle for 10 min with a flow rate of approximately 1 liter per minute to remove blood from the fillet. Superchilling and storage In order to quantify the quality effect of the superchilling process, one fillet from each fish was superchilled, while the other fillet was subjected to traditional top icing with wet ice. The superchilling was performed with a Nitrogen freezer (AGA mini Freezer, AGA, Linde Gas, Stavanger, Norway) using liquid Nitrogen (Biogon N liquid, AGA, Linde Gas, Stavanger, Norway)
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W = 100 −
(100 − L ∗ )2 + a ∗2 + b ∗2
(1)
and Chroma (C∗ ) were calculated as: C∗ =
a ∗2 + b ∗2
(2)
Computer image analysis/fillet contraction Percentage fillet contraction was measured on all the fillets in the design (n = 80) similarly as described in Stien and others (2005), but instead of a sequence of images throughout storage there was one image pre- and one image poststorage of each fillet. In short, the fillets were placed on a dark base together with a 30-cm-long yellow lineal for scale and depicted one at the time. For each image, an automatic image analysis algorithm first segmented the whitish fillet region and the yellow lineal region from the dark background, then estimated the lengths of these 2 regions as the length of the smallest rectangle containing each respective region and translated the fillet lengths in pixels to cm for easy comparison between pre- and poststorage images. Fillet length in cm = fillet length in pixels/ lineal length in pixels ∗ 30 cm.
(3)
Percentage fillet contraction = 100 (1 − fillet length post storage in cm/ fillet length pre storage in cm)
(4)
temperature around the initial freezing point (data not shown). Drip loss Drip loss (DL) during storage was measured on all the fillets in Initial freezing point for Atlantic cod has been reported to be between –0.8 and –1.3, depending on ambient sea temperature the design (n = 80) gravimetrically according to the formula (Simpson and Haard 1987), which confirms that the fillets in this W0 − W1 trial were not chilled to hard, but could actually have been chilled ∗ 100 (5) DL = a bit more. W0 Traditionally iced fillets had an initial temperature of 6.5 °C, where W0 is initial fillet weight, and W1 is fillet weight after and used the 1st 24 h to reach 0 °C (Figure 1). It is likely 7 d. The fillets were dried before weighing to remove excess to believe that the temperature during transportation was subwater. zero, as both superchilled and traditionally chilled fillets decreased 0.2 °C in temperature during transportation, which brought the Texture analysis iced fillets to subzero conditions. After transportation, the iced filThe textural parameter’s hardness and breaking force (puncture lets gradually increased up to 0.0 °C again, while the superchilled test) were measured on all the fillets in the design (n = 80) with a fillets stayed subzero all 7 d. Similar result was obtained when cod R -plus Texture Analyzer, Stable Micro loins were superchilled to approximately –1.0 °C. They were storTexture Analyzer (TA-XT2 Systems, Surrey, UK) with a load cell of 50 kg. A flat-ended cylin- age at 0.5 °C for up to 14 d and had an average temperature of –0.3 der (25 mm) was used as test probe, and the probe speed during ± 0.5 °C (Olafsdottir and others 2006). Superchilling as a single compression was constant at 1 mm/s. On each fillet, the puncture operation followed by storage in chilled conditions seems to have a test was assessed on 2 locations, specifically on the anterior part good effect on keeping the products subzero under chilled storage. of the loin. By using specific macros in the Exponent software Shelf life was not a topic in this study, but several studies has (Exponent, Version 4.0.3.0, Stable Micro Systems, Surrey, UK) shown that superchilling gave shelf life extension on several fish included with the Texture Analyzer, the force at 80%, 60%, 40%, species (Kaale and others 2011). Olafsdottir and others (2006) and 20% compression of the initial sample height (firmness) were found an increase in shelf life of 20% when comparing tradiassessed together with the breaking force recorded during the as- tional iced cod fillets (average temp approximately 2 °C) with sessment. Mean values of the 2 assessments were used for statistical superchilled (average temp approximately –0.5) while Duun and analyses of the data. Rustad (2007) reported almost no increase of bacterial growth during 5-wk storage of vacuum-packaged cod loins stored at –2.2 ± Statistics 0.2 °C. Combining superchilling with modified atmosphere (MA) Analysis of variance (general linear model [GLM]) was per- packaging has shown a synergic effect, almost doubling the shelf formed with Minitab 15 (Minitab, Coventry, UK). GLM was life of cod loins (Lauzon and others 2009). performed using Tukey’s honestly significance difference test at level P < 0.05 to obtain confidence intervals for all differences between level means. All results are given as mean ± SD unless Color and blood removal As demonstrated in Figure 2, pictures taken from a random samother is stated. ple from both groups only minutes after skinning show no signs of residual blood, where both groups appear to be well exsanResults and Discussion guinated. This impression followed throughout the experiments Temperature profile where color measurements 7 d later show no significant difference Temperature logging during transportation and storage showed (P > 0.07) between processing or chilling method in any of the that the superchilled fillets had an equilibrium temperature of measured parameters having an average of L∗ = 83.03 ± 1.55, –0.7 ± 0.1 °C (Figure 1). A short pretest was set up to find a∗ = –3.01 ± 0.91, b∗ = 14.52 ± 0.89, C∗ 15.01 ± 0.81, and the optimum super chilling conditions, giving the fillets a core W = 77.41 ± 1.14. Current results on a∗ are far less than what 7 Wet ice 6
Superchilling
Temperature (°C)
5
Figure 1–Temperature profile of superchilled (gray) and traditionally top iced fillets of Atlantic cod (Gadus morhua) during transport (2 d) and storage (5 d) in chilled conditions (approximately 0 °C).
4 3 2 1 0
-1 -2 0
12
24
36
48
60
72 84 Time (hours)
96
108
120
132
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Direct filleting and superchilling . . .
Direct filleting and superchilling . . . Fillet contraction and DL In correspondence with others on salmon (Bahuaud and others 2008), superchilling of Atlantic cod resulted in less fillet shrinkage (P < 0.005) than traditionally iced fillets (Table 1). For whitefish, such as Atlantic cod, the degree of shrinkage can vary from 5.4% to 15.5% depending on the seawater temperature and stress (Jørpeland and others 2013). This is within reason as lower temperature will postpone the onset of rigor mortis. Fillet contraction of farmed Atlantic cod increases both in degree and speed with increasing temperature (Mørkøre and others 2004), as sited in Mørkøre (2006). Rigor development in cod fillets has shown to be related to the decrease and consumption of glycogen (Cappeln and Jessen 2002), and even though Adenosine triphosphate degradation appears to be faster in superchilled salmon fillets, the decrease of pH over time was decreased by superchilling (Gaarder and others 2012). This might imply that breakdown of glycogen is slowed down by superchilling and causing reduces fillet shrinkage
Figure 2–Pictures from traditional processed fillets (below) and direct processed fillets (above) only minutes after spray washing. 14
b
12
% - drip loss
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has been reported on cod operating with a∗ values in the range of −1.8 (Digre and others 2011a) and 2.7 to 5.4 (Jørpeland and others 2013). Furthermore, Digre and others (2011b) found a significantly higher redness in fillets that were direct gutted as compared to traditionally gill cutting. They only washed the body cavity briefly with running water and did not rinse the fillets with fresh water as done in the present study. This demonstrates the importance of filleting and washing in the current experiment, where the procedure of direct filleting followed by spray rinsing had a positive effect on blood removal. A previous study on Atlantic salmon showed that one of the most important factors for removing the blood from the fillet is not only timing for exsanguination, but also filleting as prerigor filleted fillets had in general 4 folds less blood spots than postrigor filleted fish (Roth and others 2009b). Reason seems to lay in the bloods ability to clot, where prerigor filleting opens all the veins allowing the blood to flow out before clotting.
Super chilling
10 8 6
d
Traditional ice
a
4
c
2 0 Direct filleting
Traditional filleting
Bleeding protocol
Figure 3–Effect of bleeding protocol (Direct filleting compared with Traditional filleting) and packaging method (superchilling compared with traditional top icing) on drip loss of pre-rigor filleted Atlantic cod (Gadus morhua) during transport and storage in chilled conditions (approximately 0° C). Means with different lowercase superscript are significant different by ANOVA and Tukey’s pairwise comparison test (P < 0.05).
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Direct filleting and superchilling . . . Table 1–Effect of bleeding protocol (traditional or direct filleting) and packaging method (superchilled without ice or traditionally iced) on drip loss, fillet shrinkage, breaking force, and compression force at 20%, 40%, 60%, and 80% of sample height.
Fillet shrinkage (%) Blood removal protocol (n = 40) Traditional 11.05 ± 5.84 Direct filleted 10.38 ± 5.13 P-value 0.524 Packaging method (n = 40) Superchilled 6.86 ± 3.37 Traditional iced 14.66 ± 4.25 P-value 0.5) difference between the 2 blood removal protocols was observed (Table 1). Question rises on what impact superchilling will have on DL. As shown in Figure 3 both chilling and blood removal protocol had a significant (P < 0.005) effect on the DL. Superchilling reduced the DL with 57% compared to traditionally icing independent of blood removal protocol, while traditional gill cut had decreased DL by 37% compared to direct gutting, independent of packaging method. The same effect has been observed by others as Duun and Rustad (2007) found superchilling combined with superchilled storage to decrease the DL in vacuum packed farmed cod, where superchilled fillets never exceeded 1.5% and iced fillets were up to 5.5%. In our experiment, ice crystals were present between the superchilled fillets, and it is likely to believe that this helped retain water in the fillet. Sivertsvik and others (2003) found no effect of superchilling on DL of MA-packaged salmon stored at –2.2 °C, while superchilled MA-packaged salmon stored at +5 °C had increased DL compared to nonsuperchilled (Bahuaud and others 2008). However, a superchilling procedure, where the fillets were stored in freezer at –25 °C for 45 min giving a core temperature at –1.5 °C, resulted in large intra- and extracellular ice crystals. It is likely to believe that this caused rupture of the cell wall, giving increased DL. In the present study, the whole fillet was flexible when the fillet had reached temperature equilibrium (after approximately 1 h) and the temperature of the fillet was at the initial freezing temperature (Figure 1). Blood removal protocol had a significant effect on the DL (Table 1). Carp muscle has shown approximately 4% increase in weight caused by osmosis after 1 h in fresh water (Nakayama and others 1995), and it is likely to believe that the rinsing with fresh water in the present study caused an uptake of water in the surface of the fillet. This water will be loosely bound, and would contribute to the increased DL that the fillets from the new blood removal protocol encountered.
Texture analysis Thickness of the loin (mm) has been shown to have a significant effect on the assessed firmness of raw and smoked fillets of Atlantic salmon (Salmo salar) (Roth and others 2009a), where increasing sample height caused the fillet firmness to decrease (R = –0.43, P < 0.001, ANCOVA). Including sample height as a covariate in the ANOVA of our data did not reveal any significant (P > 0.111) relationship between sample height and loin firmness. Neither blood removal protocol (direct gutting compared with gill cutting) nor packaging method (traditional icing compared
with superchilling) had a significant (P < 0.05) effect on texture at 40%, 60%, or 80% (Table 1). In addition, no significant (P > 0.100) effect of any of the design factors was found on the breaking force. This is in conjunction with other studies on texture in superchilled cod fillets (Gallart-Jornet and others 2007; Bahuaud and others 2008) and comparable to texture data on wild caught Atlantic cod (Rotabakk and others 2011). However, both blood removal protocol (P < 0.047) and packaging method (P < 0.012) had significant effect on the assessed firmness at 20% compression (Table 1). Significantly higher force was needed to compress the muscle of traditionally iced fillets to 20%. In addition, fillets from traditionally gill cut cod required significantly higher force to be compressed 20% than fillets form directly gutted cod. A plausible explanation for the observed softer texture in the fillets from directly gutted cod is the water rinsing of the fillets. As shown for DL, it is likely to believe that water has been absorbed by the surface of the fillets, and thus giving a softer texture in the surface. No significant differences in texture further down in the fillet strengthen this theory.
Conclusion Direct filleting combined with spray washing ensures proper exsanguination of the fillet. Adding superchilling to the process to ensure more effective chilling reduced fillet shrinkage and DL as compared to traditional iced fillet. Spray washing could cause water uptake, hence higher DL. However, several issues should have been investigated further; question rises whether spray washing combined with superchilling causes higher water holding capacity and if spray washing causes water uptake. We conclude that processing fillets through one step is feasible and would be of great importance for the industry.
Acknowledgments We greatly acknowledge the valuable technical support of Kjeld Vigsø at Aga Norway together with the hospitality and valuable help at Brødrene Larsen eft. (SF-185) conducting the field part of this trial.
Author Contribution B.T. Rotabakk designed the study, collected and interpreted the data, and drafted the manuscript. H. Bleie designed the study, and collected the data. L. H. Stien collected the data for the fillet contraction. B. Roth designed the study, interpreted the data, and drafted the manuscript.
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Compression force of sample height (%)
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Cappeln G, Jessen F. 2002. ATP, IMP, and glycogen in cod muscle at onset and during development of rigor mortis depend on the sampling location. J Food Sci 67(3):991–95. Digre H, Erikson U, Aursand IG, Gallart-Jornet L, Misimi E, Rustad T. 2011a. Rested and stressed farmed Atlantic cod (Gadus morhua) chilled in ice or slurry and effects on quality. J Food Sci 76(1):S89–100. Digre H, Erikson U, Misimi E, Standal IB, Gallart-Jornet L, Riebroy S, Rustad T. 2011b. Bleeding of farmed Atlantic cod: residual blood, color, and quality attributes of pre- and postrigor fillets as affected by perimortem stress and different bleeding methods. J Aquat Food Prod Technol 20(4):391–411. Duun AS, Rustad T. 2007. Quality changes during superchilled storage of cod (Gadus morhua) fillets. Food Chem 105(3):1067–75. Gaarder MO, Bahuaud D, Veiseth-Kent E, Morkore T, Thomassen MS. 2012. Relevance of calpain and calpastatin activity for texture in super-chilled and ice-stored Atlantic salmon (Salmo salar L.) fillets. Food Chem 132(1):9–17. Gallart-Jornet L, Rustad T, Barat JM, Fito P, Escriche I. 2007. Effect of superchilled storage on the freshness and salting behaviour of Atlantic salmon (Salmo salar) fillets. Food Chem 103(4):1268–81. Haard NF. 1993. Technological aspects of extending prime quality of seafood. J Aquat Food Prod Technol 1(3–4):9–27. Jørpeland G, Imsland A, Stien LH, Bleie H, Roth B. 2013. Effects of filleting method, stress, storage and season on the quality of farmed Atlantic cod (Gadus morhua L.). Aquac Res doi: 10.1111/are.12312. Kaale LD, Eikevik TM, Rustad T, Kolsaker K. 2011. Superchilling of food: a review. J Food Eng 107(2):141–6. Lauzon HL, Magnusson H, Sveinsdottir K, Gudjonsdottir M, Martinsdottir E. 2009. Effect of brining, modified atmosphere packaging, and superchilling on the shelf life of cod (Gadus morhua) loins. J Food Sci 74(6):M258–67. Mørkøre T. 2006. Relevance of dietary oil source for contraction and quality of pre-rigor filleted Atlantic cod, Gadus morhua. Aquaculture 251(1):56–65. Mørkøre T, Hansen SJ, Rørvik KA. 2004. Quality of pre-rigor cod fillets. Storage temperature affects contraction and gaping. Program conference (NRC), Fish farming. Clarion Hotel Oslo Airport, Gardermoen, Norway. Nakayama T, Liu DJ, Ooi A. 1995. Tension development of carp muscle immersed in pure water and CaCl2 solution. Fish Sci 61(5):822–7.
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Olafsdottir G, Lauzon HL, Martinsdottir E, Oehlenschlager J, Kristbergsson K. 2006. Evaluation of shelf life of superchilled cod (Gadus morhua) fillets and the influence of temperature fluctuations during storage on microbial and chemical quality indicators. J Food Sci 71(2): S97–109. Park JW. 1994. Functional protein additives in surimi gels. J Food Sci 59(3):525– 7. Robb DHF, Phillips AJ, Kestin SC. 2003. Evaluation of methods for determining the prevalence of blood spots in smoked Atlantic salmon and the effect of exsanguination method on prevalence of blood spots. Aquaculture 217(1–4):125–38. Rotabakk BT, Skipnes D, Akse L, Birkeland S. 2011. Quality assessment of Atlantic cod (Gadus morhua) caught by longlining and trawling at the same time and location. Fish Res 112(1– 2):44–51. Roth B, Birkeland S, Oyarzun F. 2009a. Stunning, pre slaughter and filleting conditions of Atlantic salmon and subsequent effect on flesh quality on fresh and smoked fillets. Aquaculture 289(3–4):350–6. Roth B, Obach A, Hunter D, Nortvedt R, Oyarzun F. 2009b. Factors affecting residual blood and subsequent effect on bloodspotting in smoked Atlantic salmon fillets. Aquaculture 297(1– 4):163–8. Simpson MV, Haard NF. 1987. Temperature-acclimation of atlantic cod (Gadus morhua) and its influence on freezing-point and biochemical-damage of post mortem muscle during storage at 0-degrees and 3-degrees-C. J Food Biochem 11(1):69–93. Sivertsvik M, Rosnes JT, Kleiberg GH. 2003. Effect of modified atmosphere packaging and superchilled storage on the microbial and sensory quality of Atlantic salmon (Salmo salar) fillets. J Food Sci 68(4):1467–72. Stien LH, Hirmas E, Bjornevik M, Karlsen O, Nortvedt R, Rora AMB, Sunde J, Kiessling A. 2005. The effects of stress and storage temperature on the colour and texture of pre-rigor filleted farmed cod (Gadus morhua L.). Aquac Res 36(12):1197–206. Stien LH, Suontama J, Kiessling A. 2006. Image analysis as a tool to quantify rigor contraction in pre-rigor-filleted fillets. Comput Electron Agric 50(2):109–20. Vold M, Hanssen O. 2010. Value chain analyses of different types of distribution packaging for fresh fish fillets. 17th IAPRI World Conferences. Tianjin, China.
A total of 40 farmed Atlantic cod (Gadus morhua) were in 2 groups either fillet directly after stunning and spray washed or produced into fillets according to traditional slaughter methods including exsanguination for 30 min, gutting and washing. Both groups were either stored superchilled or traditionally on ice. After 7 d postmortem color (CIE L∗ , a∗ , b∗ ) and fillet shrinkage was measured by computer imaging along with drip loss and texture hardness. Results show that superchilled fillets had significant lower core temperature than fillets stored on ice during the entire 7 d storage period. This resulted in reduced fillet shrinkage from 14.7% to 6.9% and less drip loss dropping from 9.45% to 3.99% in average. Processing the fish directly into fillets resulted in satisfactory blood drainage, where all groups were in particularly well exsanguinated with a∗ values below zero. No color difference was observed between filleting groups or chilling methods. Spray washing of the fillets resulted in water uptake and higher drip loss in interaction with chilling method. We conclude that filleting farmed fish in one step is feasible.
Keywords: farmed cod, novel process, prerigor, quality, superchilling
Traditionally farmed fish are slaughtered and processed over several steps, which often include live chilling, stunning, exsanguination, chilling, gutting, rinsing, decapitation, filleting before the fillets are packed into polystyrene boxes and shipped with ice. These processes are often time, laboring, space, and energy consuming. A novel processing line for filleting of farmed fish is gutting and filleting the fish directly after decapitation and replacing exsanguination with spray washing the fillets. In addition, all the cooling steps are replaced by superchilling the fillets. This novel process line gives fillets with comparable if not superior quality compared to the traditional process.
Practical Application:
Introduction Traditionally farmed fish such as Atlantic salmon (Salmo salar) and Atlantic cod (Gadus morhua) are slaughtered and processed over several steps, which often include live chilling, stunning, exsanguination, chilling, gutting, rinsing, decapitation, filleting before the fillets are packed into polystyrene boxes and shipped with ice. These processes are often time, laboring, space, and energy consuming, as the fish are placed into large refrigerated sea water tanks for chilling, exsanguination, and washing between each step that requires manually handling of fish into machines. Basically many of these steps are considered as suboptimal for industrialized processing for farmed fish. For exsanguination, previous studies have shown that timing is most important, not the way exsanguination is performed, where major veins must be cut (Robb and others 2003). This means that instead of exsanguination, the fish can be directly gutted (Roth and others 2009b). For Atlantic cod, direct gutting has shown to cause higher redness of the flesh (Digre and others 2011b), but the question rises whether the carcass were properly washed, which is crucial for blood removal of the muscle (Roth and others 2009b). In order to remove blood from the fillet, early filleting MS 20131732 Submitted 11/21/2013, Accepted 2/17/2014. Authors Rotabakk and Roth are with Nofima AS, Processing Technology Dept., Box 8034, N-4068 ˚ Stavanger, Norway. Author Bleie is with Atlantic cod farms AS, N-6005 Alesund, Norway. Author Stien is with Inst. of Marine Research, N-5392 Storebø, Norway. Direct inquiries to author Rotabakk (E-mail: [email protected]).
R C 2014 Institute of Food Technologists
doi: 10.1111/1750-3841.12437 Further reproduction without permission is prohibited
in combination with washing and gravity is the major mechanism for removing blood from the muscle, where prerigor filleted fillets had 5 folds less blood than postrigor filleted fish (Roth and others 2009b). This means that most of the blood will follow the carcass, while the little blood that remains in the muscle will be cleaned out quickly when prerigor filleted. Superchilling is an emerging technique that maintains food quality and safety while retaining food at a higher temperature than “normal” for frozen storage, at temperature around the initial freezing point of the food, typical around –1 °C for cod (Simpson and Haard 1987). Generally, the shelf life of superchilled food is extended compared to traditionally chilled foods, primarily because of decreased autolytic and microbiological activity at the subzero temperatures (Haard 1993). Correspondingly, the sensory quality has proven to be increased that of fresh cod (Olafsdottir and others 2006), and increased bacterial quality (Olafsdottir and others 2006; Duun and Rustad 2007), hence increased shelf life. Superchilling represents a technology that can greatly reduce the need for ice during chilled transport, enabling efficient transport and decreased emission in the packaging and distribution processes (Vold and Hanssen 2010). For fish that are filleted postrigor, the muscle is still attached to the skeleton when it undergoes rigor mortis. Consequently, the postrigor fillet will be less exposed to shrinkage in longitudinal direction than fish being filleted prerigor, but may instead lead to increased amount of fillet gaping. When fish are filleted prerigor, the muscle is free to contract and therefore undergoes shortening and the thickness of the fillet increases (Stien and others 2006; Vol. 79, Nr. 5, 2014 r Journal of Food Science E881
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Abstract:
Direct filleting and superchilling . . .
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Jørpeland and others 2013). Premortem stress and temperature is know to affect postmortem processes such as drip loss (DL), muscle contraction speed and degree of muscle shortening (Stien and others 2005; Jørpeland and others 2013). How superchilled prerigor fillets from Atlantic cod will act during rigor is still not investigated. One futuristic scenario for industrialized slaughter of fish would be to skip all steps and instead, immediately after stunning, decapitate the animal and fillet the carcass directly, before spray rinsing and concentrate all energy on chilling the fillets by superchilling. The aim of this study was therefore to investigate the effect of direct filleting and superchilling on blood removal of the muscles, color, muscle shortening, and water loss.
as a cooling media. The freezer was preset on –60 °C, and the processing time was set to 4 min. Before transport, the 4 groups were packaged in traditional expanded polystyrene boxes. Approximately 12 kg of fillets were packaged in each box, and 3 kg of ice was added in the boxes with traditionally iced fillets, according to the design. All the boxes were transported and stored under chilled conditions (approximately 0.5 °C). The fillets were under transport for 48 h and stored for additional 5 d, 7 d in total, before quality analysis. During storage, ice was added to secure excess ice, while the superchilled fillets remained unopened. In each box, the temperature of one fillet in the middle was logged every 10 min by a wireless logger (Dickson HT120, Dickson, Ill., U.S.A.).
Materials and Methods
Color Fillet surface color (CIE Lab) was assessed on all the fillets in the design (n = 80) by a digital photo imaging color-measuring system (DigiEye full system, VeriVide Ltd., Leicester, UK) after 7 d of storage. The fillets were placed in a standardized lightbox with daylight (6400 K) and photographed with a calibrated digital camera (Nikon D80, 35 mm lens, Nikon Corp., Japan). The pictures were analyzed with DigiPix software (VeriVide Ltd.) and the color quantified as an average for the whole fillet surface. L∗ describes the products lightness (L∗ = 100 = white, and L∗ = 0 = black), a∗ describes the intensity of color on the red– green axis (a∗ > 0 = red, and a∗ < 0 = green) and b∗ the intensity of color on the yellow–blue axis (b∗ > 0 = yellow, and b∗ < 0 = blue). In addition, whiteness was calculated according to Park (1994):
Raw material The experiment was carried out on 40 marked sized (2 to 4 kg) farmed Atlantic cod (Gadus morhua L.) from the North-West coast of Norway in November 2009, giving a total of 80 fillets (620 ± 146 g). All fish were starved for 2 wk before well-boat transport and rested for 2 d in sea cages before slaughter. At slaughter, the temperature in the sea was 6.5 °C. Design A full factorial design with 2 factors (blood removal protocol and chilling method) was set up. “Blood removal protocol” contained 2 variants: direct filleted and traditional and “chilling method” contained 2 variants: superchilling and traditional icing. This provided in total 4 variants with 20 fillets in each group. In addition, the left fillet of a fish was submitted to superchilling, while the right fillet was ice stored. The control was the fillets of traditionally exsanguinationed fish combined with traditional iced storage. After 7 d in expanded polystyrene boxes, the fillets were assessed for DL, shrinkage, color, and texture. Blood removal and filleting Prior to the experiment, rested fish were carefully crowded at one end of the cage (200 kg/m3 ). One fish at the time was sampled with a dip net and immediately killed by a sharp blow to the head. One group of fish (Traditional) was prerigor filleted according to traditional procedures: gill cut, followed by 30 min exsanguination in chilled seawater, then gutting, washing (tank for 15 min), decapitation, filleting and skinning. The other experimental group (Direct filleted) was immediately after killing decapitated, filleted, skinned and spray washed (10 min). For both groups, the fish were manually decapitated and gutted. The Baader 252 and Baader 51 (Baader Inc., Germany) were used for filleting and skinning, respectively. Spraywashing was conducted by manually sprinkling groups of five fillets with 4 °C fresh water using a hose with a nozzle for 10 min with a flow rate of approximately 1 liter per minute to remove blood from the fillet. Superchilling and storage In order to quantify the quality effect of the superchilling process, one fillet from each fish was superchilled, while the other fillet was subjected to traditional top icing with wet ice. The superchilling was performed with a Nitrogen freezer (AGA mini Freezer, AGA, Linde Gas, Stavanger, Norway) using liquid Nitrogen (Biogon N liquid, AGA, Linde Gas, Stavanger, Norway)
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W = 100 −
(100 − L ∗ )2 + a ∗2 + b ∗2
(1)
and Chroma (C∗ ) were calculated as: C∗ =
a ∗2 + b ∗2
(2)
Computer image analysis/fillet contraction Percentage fillet contraction was measured on all the fillets in the design (n = 80) similarly as described in Stien and others (2005), but instead of a sequence of images throughout storage there was one image pre- and one image poststorage of each fillet. In short, the fillets were placed on a dark base together with a 30-cm-long yellow lineal for scale and depicted one at the time. For each image, an automatic image analysis algorithm first segmented the whitish fillet region and the yellow lineal region from the dark background, then estimated the lengths of these 2 regions as the length of the smallest rectangle containing each respective region and translated the fillet lengths in pixels to cm for easy comparison between pre- and poststorage images. Fillet length in cm = fillet length in pixels/ lineal length in pixels ∗ 30 cm.
(3)
Percentage fillet contraction = 100 (1 − fillet length post storage in cm/ fillet length pre storage in cm)
(4)
temperature around the initial freezing point (data not shown). Drip loss Drip loss (DL) during storage was measured on all the fillets in Initial freezing point for Atlantic cod has been reported to be between –0.8 and –1.3, depending on ambient sea temperature the design (n = 80) gravimetrically according to the formula (Simpson and Haard 1987), which confirms that the fillets in this W0 − W1 trial were not chilled to hard, but could actually have been chilled ∗ 100 (5) DL = a bit more. W0 Traditionally iced fillets had an initial temperature of 6.5 °C, where W0 is initial fillet weight, and W1 is fillet weight after and used the 1st 24 h to reach 0 °C (Figure 1). It is likely 7 d. The fillets were dried before weighing to remove excess to believe that the temperature during transportation was subwater. zero, as both superchilled and traditionally chilled fillets decreased 0.2 °C in temperature during transportation, which brought the Texture analysis iced fillets to subzero conditions. After transportation, the iced filThe textural parameter’s hardness and breaking force (puncture lets gradually increased up to 0.0 °C again, while the superchilled test) were measured on all the fillets in the design (n = 80) with a fillets stayed subzero all 7 d. Similar result was obtained when cod R -plus Texture Analyzer, Stable Micro loins were superchilled to approximately –1.0 °C. They were storTexture Analyzer (TA-XT2 Systems, Surrey, UK) with a load cell of 50 kg. A flat-ended cylin- age at 0.5 °C for up to 14 d and had an average temperature of –0.3 der (25 mm) was used as test probe, and the probe speed during ± 0.5 °C (Olafsdottir and others 2006). Superchilling as a single compression was constant at 1 mm/s. On each fillet, the puncture operation followed by storage in chilled conditions seems to have a test was assessed on 2 locations, specifically on the anterior part good effect on keeping the products subzero under chilled storage. of the loin. By using specific macros in the Exponent software Shelf life was not a topic in this study, but several studies has (Exponent, Version 4.0.3.0, Stable Micro Systems, Surrey, UK) shown that superchilling gave shelf life extension on several fish included with the Texture Analyzer, the force at 80%, 60%, 40%, species (Kaale and others 2011). Olafsdottir and others (2006) and 20% compression of the initial sample height (firmness) were found an increase in shelf life of 20% when comparing tradiassessed together with the breaking force recorded during the as- tional iced cod fillets (average temp approximately 2 °C) with sessment. Mean values of the 2 assessments were used for statistical superchilled (average temp approximately –0.5) while Duun and analyses of the data. Rustad (2007) reported almost no increase of bacterial growth during 5-wk storage of vacuum-packaged cod loins stored at –2.2 ± Statistics 0.2 °C. Combining superchilling with modified atmosphere (MA) Analysis of variance (general linear model [GLM]) was per- packaging has shown a synergic effect, almost doubling the shelf formed with Minitab 15 (Minitab, Coventry, UK). GLM was life of cod loins (Lauzon and others 2009). performed using Tukey’s honestly significance difference test at level P < 0.05 to obtain confidence intervals for all differences between level means. All results are given as mean ± SD unless Color and blood removal As demonstrated in Figure 2, pictures taken from a random samother is stated. ple from both groups only minutes after skinning show no signs of residual blood, where both groups appear to be well exsanResults and Discussion guinated. This impression followed throughout the experiments Temperature profile where color measurements 7 d later show no significant difference Temperature logging during transportation and storage showed (P > 0.07) between processing or chilling method in any of the that the superchilled fillets had an equilibrium temperature of measured parameters having an average of L∗ = 83.03 ± 1.55, –0.7 ± 0.1 °C (Figure 1). A short pretest was set up to find a∗ = –3.01 ± 0.91, b∗ = 14.52 ± 0.89, C∗ 15.01 ± 0.81, and the optimum super chilling conditions, giving the fillets a core W = 77.41 ± 1.14. Current results on a∗ are far less than what 7 Wet ice 6
Superchilling
Temperature (°C)
5
Figure 1–Temperature profile of superchilled (gray) and traditionally top iced fillets of Atlantic cod (Gadus morhua) during transport (2 d) and storage (5 d) in chilled conditions (approximately 0 °C).
4 3 2 1 0
-1 -2 0
12
24
36
48
60
72 84 Time (hours)
96
108
120
132
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Direct filleting and superchilling . . .
Direct filleting and superchilling . . . Fillet contraction and DL In correspondence with others on salmon (Bahuaud and others 2008), superchilling of Atlantic cod resulted in less fillet shrinkage (P < 0.005) than traditionally iced fillets (Table 1). For whitefish, such as Atlantic cod, the degree of shrinkage can vary from 5.4% to 15.5% depending on the seawater temperature and stress (Jørpeland and others 2013). This is within reason as lower temperature will postpone the onset of rigor mortis. Fillet contraction of farmed Atlantic cod increases both in degree and speed with increasing temperature (Mørkøre and others 2004), as sited in Mørkøre (2006). Rigor development in cod fillets has shown to be related to the decrease and consumption of glycogen (Cappeln and Jessen 2002), and even though Adenosine triphosphate degradation appears to be faster in superchilled salmon fillets, the decrease of pH over time was decreased by superchilling (Gaarder and others 2012). This might imply that breakdown of glycogen is slowed down by superchilling and causing reduces fillet shrinkage
Figure 2–Pictures from traditional processed fillets (below) and direct processed fillets (above) only minutes after spray washing. 14
b
12
% - drip loss
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has been reported on cod operating with a∗ values in the range of −1.8 (Digre and others 2011a) and 2.7 to 5.4 (Jørpeland and others 2013). Furthermore, Digre and others (2011b) found a significantly higher redness in fillets that were direct gutted as compared to traditionally gill cutting. They only washed the body cavity briefly with running water and did not rinse the fillets with fresh water as done in the present study. This demonstrates the importance of filleting and washing in the current experiment, where the procedure of direct filleting followed by spray rinsing had a positive effect on blood removal. A previous study on Atlantic salmon showed that one of the most important factors for removing the blood from the fillet is not only timing for exsanguination, but also filleting as prerigor filleted fillets had in general 4 folds less blood spots than postrigor filleted fish (Roth and others 2009b). Reason seems to lay in the bloods ability to clot, where prerigor filleting opens all the veins allowing the blood to flow out before clotting.
Super chilling
10 8 6
d
Traditional ice
a
4
c
2 0 Direct filleting
Traditional filleting
Bleeding protocol
Figure 3–Effect of bleeding protocol (Direct filleting compared with Traditional filleting) and packaging method (superchilling compared with traditional top icing) on drip loss of pre-rigor filleted Atlantic cod (Gadus morhua) during transport and storage in chilled conditions (approximately 0° C). Means with different lowercase superscript are significant different by ANOVA and Tukey’s pairwise comparison test (P < 0.05).
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Direct filleting and superchilling . . . Table 1–Effect of bleeding protocol (traditional or direct filleting) and packaging method (superchilled without ice or traditionally iced) on drip loss, fillet shrinkage, breaking force, and compression force at 20%, 40%, 60%, and 80% of sample height.
Fillet shrinkage (%) Blood removal protocol (n = 40) Traditional 11.05 ± 5.84 Direct filleted 10.38 ± 5.13 P-value 0.524 Packaging method (n = 40) Superchilled 6.86 ± 3.37 Traditional iced 14.66 ± 4.25 P-value 0.5) difference between the 2 blood removal protocols was observed (Table 1). Question rises on what impact superchilling will have on DL. As shown in Figure 3 both chilling and blood removal protocol had a significant (P < 0.005) effect on the DL. Superchilling reduced the DL with 57% compared to traditionally icing independent of blood removal protocol, while traditional gill cut had decreased DL by 37% compared to direct gutting, independent of packaging method. The same effect has been observed by others as Duun and Rustad (2007) found superchilling combined with superchilled storage to decrease the DL in vacuum packed farmed cod, where superchilled fillets never exceeded 1.5% and iced fillets were up to 5.5%. In our experiment, ice crystals were present between the superchilled fillets, and it is likely to believe that this helped retain water in the fillet. Sivertsvik and others (2003) found no effect of superchilling on DL of MA-packaged salmon stored at –2.2 °C, while superchilled MA-packaged salmon stored at +5 °C had increased DL compared to nonsuperchilled (Bahuaud and others 2008). However, a superchilling procedure, where the fillets were stored in freezer at –25 °C for 45 min giving a core temperature at –1.5 °C, resulted in large intra- and extracellular ice crystals. It is likely to believe that this caused rupture of the cell wall, giving increased DL. In the present study, the whole fillet was flexible when the fillet had reached temperature equilibrium (after approximately 1 h) and the temperature of the fillet was at the initial freezing temperature (Figure 1). Blood removal protocol had a significant effect on the DL (Table 1). Carp muscle has shown approximately 4% increase in weight caused by osmosis after 1 h in fresh water (Nakayama and others 1995), and it is likely to believe that the rinsing with fresh water in the present study caused an uptake of water in the surface of the fillet. This water will be loosely bound, and would contribute to the increased DL that the fillets from the new blood removal protocol encountered.
Texture analysis Thickness of the loin (mm) has been shown to have a significant effect on the assessed firmness of raw and smoked fillets of Atlantic salmon (Salmo salar) (Roth and others 2009a), where increasing sample height caused the fillet firmness to decrease (R = –0.43, P < 0.001, ANCOVA). Including sample height as a covariate in the ANOVA of our data did not reveal any significant (P > 0.111) relationship between sample height and loin firmness. Neither blood removal protocol (direct gutting compared with gill cutting) nor packaging method (traditional icing compared
with superchilling) had a significant (P < 0.05) effect on texture at 40%, 60%, or 80% (Table 1). In addition, no significant (P > 0.100) effect of any of the design factors was found on the breaking force. This is in conjunction with other studies on texture in superchilled cod fillets (Gallart-Jornet and others 2007; Bahuaud and others 2008) and comparable to texture data on wild caught Atlantic cod (Rotabakk and others 2011). However, both blood removal protocol (P < 0.047) and packaging method (P < 0.012) had significant effect on the assessed firmness at 20% compression (Table 1). Significantly higher force was needed to compress the muscle of traditionally iced fillets to 20%. In addition, fillets from traditionally gill cut cod required significantly higher force to be compressed 20% than fillets form directly gutted cod. A plausible explanation for the observed softer texture in the fillets from directly gutted cod is the water rinsing of the fillets. As shown for DL, it is likely to believe that water has been absorbed by the surface of the fillets, and thus giving a softer texture in the surface. No significant differences in texture further down in the fillet strengthen this theory.
Conclusion Direct filleting combined with spray washing ensures proper exsanguination of the fillet. Adding superchilling to the process to ensure more effective chilling reduced fillet shrinkage and DL as compared to traditional iced fillet. Spray washing could cause water uptake, hence higher DL. However, several issues should have been investigated further; question rises whether spray washing combined with superchilling causes higher water holding capacity and if spray washing causes water uptake. We conclude that processing fillets through one step is feasible and would be of great importance for the industry.
Acknowledgments We greatly acknowledge the valuable technical support of Kjeld Vigsø at Aga Norway together with the hospitality and valuable help at Brødrene Larsen eft. (SF-185) conducting the field part of this trial.
Author Contribution B.T. Rotabakk designed the study, collected and interpreted the data, and drafted the manuscript. H. Bleie designed the study, and collected the data. L. H. Stien collected the data for the fillet contraction. B. Roth designed the study, interpreted the data, and drafted the manuscript.
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Compression force of sample height (%)
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