- Email: [email protected]
Evaluating instrumental colour and texture of thermally treated New Zealand King Salmon (Oncorhynchus tshawytscha) and their relation to sensory properties
LWT - Food Science and Technology 44 (2011) 1814e1820
Contents lists available at ScienceDirect
LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt
Evaluating instrumental colour and texture of thermally treated New Zealand King Salmon (Oncorhynchus tshawytscha) and their relation to sensory properties Danaé Larsen, Siew-Young Quek*, Laurence Eyres Food Science Programme, Department of Chemistry, The University of Auckland, 23 Symonds Street, Auckland, New Zealand
a r t i c l e i n f o
a b s t r a c t
Article history: Received 1 March 2010 Received in revised form 15 March 2011 Accepted 16 March 2011
Farmed New Zealand King Salmon (Oncorhynchus tshawytscha) was prepared according to common consumer techniques, namely poached, steamed, microwaved, pan fried (no oil), oven baked (no oil) and deep fried (in sunflower oil). Colour and texture were measured instrumentally and a sensory evaluation comprising of a generic QDA was conducted for the intensity and overall liking of the properties of colour, texture, flavour and aroma. During the thermal treatment (cooking), the outer colour of the King Salmon fillets became lighter, more red and yellow. Thermal treatment increased the texture firmness, chewiness and springiness of King Salmon as measured by texture analyser. Overall, the sensory panel preferred the oven baked King Salmon but least liked the poached and microwaved King Salmon. The instrumental texture measurements of the cooked King Salmon were closely linked with the texture ratings from the sensory panel. These experiments provide useful data for determining the optimal preparation techniques that in turn can facilitate the farming of NZ King Salmon to directly benefit the consumer. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: King Salmon Sensory properties Colour Texture
1. Introduction Consumers are becoming increasingly aware of the beneficial effects of including long chain polyunsaturated fatty acids (LCPUFA) in the diet. There have been several studies showing the positive effect that LCPUFA, in particular the omega-3 fatty acids (n-3 FA), EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) has on a range of health problems. An increased intake of LCPUFA has shown to have beneficial effects on atherosclerosis progression (Erkkila, Lichtenstein, Mozaffarian, & Herrington, 2004) and protecting against cardiovascular disease (He et al., 2004). Several epidemiological studies have also shown favourable effects on inflammation and endothelial function (He et al., 2009), with studies also showing the therapeutic benefit of LCPUFA in rheumatoid Arthritis treatment (Darlington & Stone, 2001). LCPUFA are also beneficial in promoting infant brain development and eye function (Birch, Hoffman, Uauy, Birch, & Prestidge, 1998) and have been found to be inversely associated with chronic depression symptoms in women (Colangelo, He, Whooley, Daviglus, & Liu, 2009). Humans cannot synthesise n-3 FA, instead they have to obtain n-3 fatty acids from those that pass through the food chain and
* Corresponding author. Tel.: þ64 9 3737599x85852; fax: þ64 9 373 7422. E-mail address: [email protected] (S.-Y. Quek). 0023-6438/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2011.03.018
become incorporated in fish and marine mammals. A good source of n-3 fatty acids is from oily fish, in particular the Salmon species. Even though there is an increased consumer awareness of increasing the intake of fatty fish, such as Salmon in the diet, many people in Western countries are still not eating the recommended level (Krutulyte et al., 2008). Previous studies by Trondsen, Scholderer, Lund, and Eggen (2003) and Verbeke and Vackier (2005) revealed that the perceived time-consuming nature of preparing fish and the sensory properties, most notably taste, are the predominant contributors to why consumers are reluctant to increase their fatty fish intake even though the health benefits are now widely known. In New Zealand, King Salmon is generally consumed in a cooked state. Previous research on the effect of cooking method on the LCPUFA levels in King Salmon was undertaken by Larsen, Quek & Eyres (2010) and it was found that regardless of cooking method, NZ King Salmon is a good source of LCPUFA. However, to get consumers to include more LCPUFA in their diets, it is important to understand the effect that different preparation techniques have on the sensory properties of the salmon as sensory properties play a vital role in consumption choices. The sensory parameters that are important in determining the consumption of fish include colour, texture, flavour and aroma (Sigurgisladottir et al., 1999). The objective of this research was to study the effect of different heat treatment (cooking) methods on the key sensory properties in
D. Larsen et al. / LWT - Food Science and Technology 44 (2011) 1814e1820
NZ King Salmon using instrumental colour and texture measurements and a sensory evaluation to obtain an idea on the optimal preparation techniques to fulfil consumer satisfaction.
2. Materials and methods 2.1. Materials and sample preparation Fresh King Salmon was supplied by the New Zealand King Salmon Company, Nelson, New Zealand. All fish was transported to the laboratory chilled. The King Salmon was obtained as fillets without skin (MayeAugust, 2007). All samples were taken from the same sample area (Fig. 1). Each measurement conducted was taken from 9 separate fish with each individual fish sampled in triplicate. One hundred gram samples of Salmon were cooked from fresh, following AOAC 976.16 (method for cooking seafood) (AOAC, 1999), where the Salmon reached an internal temperature of 70 C for each cooking method. A sample size of 27 was used for each cooking method. Different heat treatments were selected as common cooking procedures used by consumers. These were poaching, steaming, microwaving, pan frying, oven baking and deep frying. All these methods were undertaken without the addition of salt or oil apart from deep frying which used sunflower oil. Poaching e the King Salmon samples were placed in a stainless steel pot of boiling water (500 mL) with the lid on for 3 min and 30 s. After this, the samples were removed and drained on absorbent paper towels. Pan frying e the King Salmon samples were positioned in a nonstick frying pan (180 C) bone side down for 3 min, then skin side down for 3 min. Each short side was then cooked for 1 min. Total cooking time per sample was 8 min. The cooking temperature was monitored with a digital probe. After cooking, the pan was wiped with pre-weighed absorbent paper towels to obtain the weight of excess oil exuded during cooking. Microwaving e the King Salmon samples were individually placed on a pre-weighed ceramic plate and cooked on full power for 40 s (Panasonic Genius, Japan). The samples were then placed on pre-weighed absorbent paper towels. Oven baking e the King Salmon samples were put in a preweighed Teflon lined stainless steel baking dish and cooked in a convection oven at 180 C for 10 min. The samples were then removed and the excess oil absorbed onto pre-weighed paper towels which were weighed to obtain the weight of excess oil exuded during cooking. Steaming e the King Salmon samples were placed in a stainless steel steamer above a stainless steel pot of boiling water (500 mL)
Fig. 1. Sampling location on King Salmon fillet.
1815
with the lid on for 5 min and 30 s. After this, the King Salmon samples were placed on absorbent paper towels. Deep frying e the King Salmon samples were placed in a wire mesh basket and immersed in sunflower oil in a deep fryer (Sanyo easy clean, Japan) for 5 min at 180 C. After frying, the basket was shaken and the samples placed on absorbent paper towels. After each of the heat treatments, the samples were cooled to room temperature and weighed to obtain the cooked % yield, colour and texture were then measured. 2.2. Analytical procedures 2.2.1. Colour Instrumental colour analyses of the King Salmon fillets were conducted using a CR300 colourimeter (Minolta, Osaka, Japan). Measurements were made directly on the fillet, where L* value describes lightness, a* value redness and b* value yellowness as recommended by CIE 1976 (Commission Internationale de l’Eclairage, Vienna, Austria). Instrumental colour measurements were taken on the surface of each side of the fillet sample (“outer fillet”) as well as on the flesh inside the fillet (“inner fillet”) with triplicate measurements. All colour testing of King Salmon was carried out before and immediately after cooking, once the samples had reached room temperature. 2.2.2. Texture Initially the texture of raw King Salmon was tested to determine texture variation due to anatomical location along the whole fillet. It was found that the locations near the tail end (approximately 10 cm from end of tail) were significantly softer than the locations near the head or in the centre. This was also observed in the study by Sigurgisladottir et al. (1999) which observed that sampling locations closer to the tail of the fish were more sensitive to breaking than those from the head sections. This is probably due to differences in musculature throughout the fish flesh and therefore variations within individuals exist according to anatomical location. In the current study, all samples were taken from the central region of the fillets where there was no significant difference in texture prior to cooking. The raw and cooked fillet portions were cooled to room temperature (19 1 C). A smaller sample section was cut from each fillet portion (3 cm 3 cm 3 cm). A TA.XT2 Texture Analyser (Stable Micro System, Surrey, England) with two different probe attachments were used; a spherical probe to specifically assess the compression of the Salmon flesh and a tooth probe to mimic the human bite as it shears the Salmon flesh. Double compression was applied to construct the texture profile analyses (TPA) parameters following the method modified from Sigurgisladottir et al. (1999). The spherical probe (25 mm diameter) approached the sample at a pre test speed of 2 mm/s and then penetrated 5 mm into the fillet at a test speed of 2 mm/s. The fillet was then allowed to rebound for 15 s by reducing the force of the sphere so that it just touched the surface of the fillet. The sphere was then pressed onto the fillet again resulting in a double compression. The sphere then returned to its starting position at a post-test speed of 2 mm/s. The tooth probe (10 mm) was positioned perpendicular to the muscle fibers in the samples. The tooth probe approached the sample at a pre test speed of 2 mm/s and then penetrated 5 mm into the fillet at a test speed of 2 mm/s. The probe then returned to its starting position at a post-test speed of 2 mm/s. Each texture measurement was conducted in triplicate. Cohesiveness and springiness were measured from the TPA and chewiness was calculated as a product of hardness, springiness and cohesiveness.
1816
D. Larsen et al. / LWT - Food Science and Technology 44 (2011) 1814e1820
2.3. Sensory evaluation
2.4. Statistical analysis
A sensory evaluation was conducted by recruiting 50 nontrained participants. The participants ranged in age from 19 to 50 years, 18 male, 32 female, and were from various ethnic groups. The participants fish consumption habits ranged from less than once per month to at least 3 times per week, and their salmon consumption ranged from less than once per month to once per week. The sensory evaluation was carried out in specialised sensory booths. The evaluation area had a controlled environment, which was noise and distraction free and ensured conditions remained the same throughout the trials. A hatch system was utilised in which the samples were passed from the preparation area to the panellists, so they could not visibly see the preparation area. Each booth was equipped with a score sheet, pen, a spittoon, serviettes, a glass of clear apple juice and a glass of filtered water with unlimited supply. The score sheet had instructions for the panellists to follow which reiterated those verbally given at the beginning of the session. Panellists were instructed to rinse their mouths with apple juice and then water between samples and to expectorate into the spittoon if required. The presentation of samples was randomised and panellists always sampled from left to right and were allowed to resample during the trial if required. Detailed instructions complete with an example on how to mark the score sheet to indicate their response were included on the score sheet. Cooked King Salmon was sampled during the sensory evaluation. The King Salmon was cooked immediately before each session. After cooking, the King Salmon was cut into w25 g pieces and served at 30 C. In total six samples, one from each different cooking method was tested. The Salmon samples were given to each panellist individually to maintain a constant temperature between samples. Each cooking method was assigned a randomly generated three digit number as a reference code so that the panellists did not know the difference between samples. Panellists were asked to indicate on a 10 cm line scale how they perceived the colour intensity, flavour intensity, aroma intensity, and texture. The endpoints for each scale were “extremely soft” and “extremely hard” for texture, “extremely light” and “extremely dark” for colour intensity, “extremely weak” and “extremely strong” for aroma and flavour intensity. They were also asked to indicate how much they liked or disliked each of these components on a 10 cm line scale with the endpoints “extremely dislike “ and “extremely like”. The overall opinion of each sample was also collected using the same 10 cm line scale. The panellists were also asked to rank (from 1 to 4, with 1 being most important) their order of importance for the four key sensory properties; taste, aroma, colour and texture when they consume Salmon.
One way analysis of variance (ANOVA) and bivariate correlations were conducted using SPSS 17.0, SPSS Inc. IL, USA and a significance level of p < 0.05 was used. Principal component analysis (PCA) was conducted on the instrumental texture data and the texture data from the sensory evaluation using The UnscamblerÒ software package, v9.7, Camo Software, Norway. 3. Results and discussion 3.1. Instrumental colour analysis Comparing the inner and outer colour of raw and cooked King Salmon showed that for all methods the cooked fillets were lighter, more red and more yellow as reflected by increases in L*, a* and b* values, respectively (Table 1). Of the outer fillets of the cooked King Salmon, the deep fried and pan fried King Salmon had the lowest L* value and high a* values, indicating these methods produced samples with the darkest colour. The oven baked King Salmon had the highest b* value followed by the pan fried and oven baked King Salmon. This showed that the above methods produced samples with a more yellow colour. On the other hand, the poached King Salmon had the highest L* value and also the lowest a* and b* values, reflecting the lightest colour among the cooking methods. For the inner fillets, the deep fried and oven baked King Salmon had the highest L* values, followed by the pan fried King Salmon. The poached and microwaved King Salmon had the lowest L* values. Conversely, the poached King Salmon had the highest a* and b* values while the microwaved King Salmon had the lowest although, there was a very small difference in the red and yellow colour of the inner fillet between cooking methods. Processing affects the colour of a product through changes in the nature of the pigment or its content and/or physical state (Hutchings, 1999). During cooking of fish, the addition of heat causes protein aggregation. Opacity increases consequently causing the lightness value (L* value) to increase. The optical path length in the flesh is reduced due to the increase in opacity and as a result, the light that enters the surface has a lower chance of being selectively absorbed. This causes a drop in the perceived redness (a* value) as noted by Skrede and Storebakken (1986) in their study on Atlantic Salmon. However, the a* values did not decrease as expected, instead all the a* values for the inside and outer surface of the King Salmon samples increased on cooking, with a significant difference between raw and deep fried King Salmon (p < 0.05). There was a greater increase in redness of the outer flesh colour as expected, due to surface browning during some of the cooking methods, especially deep fried and pan fried, but unexpectedly this also occurred also in the microwaved King Salmon although there was
Table 1 Instrumental mean measurements of the inner and outer fillet colours of raw and cooked New Zealand King Salmon. Cooking method
Raw Microwaved Pan fried Poached Steamed Oven baked Deep fried
Outer fillet colour
Inner fillet colour
L*
a*
b*
L*
a*
b*
47.88 3.61a 69.01 3.17b,c,d 57.46 3.61e 73.91 2.89b,f,g 72.61 1.69c,f,h 70.13 2.94d,g,h 56.27 3.82a,e
15.88 0.76a 22.68 3.60b 22.42 2.29b 19.65 2.43b 18.78 2.36b 21.13 4.15b 24.75 1.87c
16.89 1.13a 27.04 3.22b 29.12 4.25b 25.82 3.09b 25.05 3.23b 30.19 3.87b 26.56 5.13b
51.98 1.36a 66.88 3.11b,c 74.19 2.27b,d 67.47 0.23b,c 72.51 3.81b 75.38 1.39b,d 75.05 2.90b,d
19.39 0.54a 20.53 1.07a 21.58 2.94a 22.66 5.21a 22.04 3.63a 20.72 2.89a 21.48 2.71a
21.52 0.7a 22.53 1.25a 23.42 2.77a 25.15 5.43a 23.59 3.89a 23.04 2.31a 23.83 4.4a
Different letters in the same column indicate significant differences (p < 0.05). Twenty-seven replicates per measurement.
D. Larsen et al. / LWT - Food Science and Technology 44 (2011) 1814e1820
no visible browning on the outer surface. The King Salmon in the current research has a diet supplemented with astaxanthin instead of canthaxanthin, which is less red. In a lot of the literature on farmed salmon, canthaxanthin is the most common supplement, therefore the change in redness may be due to the initial redness from the astaxanthin. The utilisation of carotenoids by salmon is improved with high dietary lipid content (Foss, Storebakken, Schiedt, Liaaen-Jensen, Austreng & Strieff, 1984). The desired redness in salmon is enhanced in fish with higher oil content because there is a greater refractive index between muscle and air than between muscle and oil (Foss et al., 1984). This means that there is less light scattering and more redness. Fish with lower oil content leads to increased light scattering and therefore lower the redness. However, this did not occur in the cooked King Salmon, probably because there are other changes that occurred during cooking as well as the changes in redness. Also, the differences in a* value between the methods may not have been large enough to show a trend with their lipid content. Only the deep fried samples were the most red and had the highest lipid content (data not shown) but this was probably due to the absorption of sunflower oil during frying than the lipid content affecting the redness. The intake of pigments and oil in the diet of King Salmon varies with season and the environment and therefore varies in the flesh. More so in the wild, this leads to different associations between carotenoid determination and visual redness. Farmed King Salmon are feed specific diets that are high in carotenoids and oil to enhance the redness of the fish and this generally causes less seasonal changes. Deep frying caused the largest difference in colour for the King Salmon. The deep fried King Salmon, however, was more red but not as yellow as some of the other samples. Possibly this was because King Salmon flesh was already quite a dark orange red and therefore, the effect of deep frying was not as pronounced as it would be in white fleshed fish. The most browning was observed in the deep fried, pan fried and oven baked King Salmon. This was most likely caused by the Maillard reactions which are caused by non-enzymic browning. The reducing sugars and free amino acids react forming colourless premelanoidins which undergo polymerisation into macromolecular melanoidins which are deep brown in colour. Also similar browning reactions are caused through oxidation products in the frying oil such as hydroperoxides or unsaturated aldehydes interacting with the free amine group of bound lysine (Pokorny, 1981). 3.2. Instrumental texture analysis Fish flesh is rheologically and structurally complex and consists of a combination of solid and fluid components (Dunajski, 1979). The properties and concentrations of the structural elements in the fish tissue and their arrangements in the muscle influence the textural properties and mouth feel (Szczesniak, 1963). The textural properties of the muscle tissue such as firmness or toughness are directed by the fibourous proteins, which are present as 70e80% of the total protein content (Dunajski, 1979). The effect on the texture due to these two types of proteins, myofibrillar proteins (present inside muscle fibers) and constituents of the connective tissue are governed by ante mortem and post-mortem factors and also by the type of processing (Dunajski, 1979). Because of the flakiness of cooked fish, measuring the texture with instruments is difficult. The positioning of the samples becomes crucial. To conduct Texture Profile Analysis (TPA), a sphere probe was used to try to get a representative analysis of the whole cooked sample. This was hindered by the weak forces of attraction between the myofibrils and between the fibers.
1817
Fish collagen is less thermally stable and more soluble than mammalian collagen as it contains less proline and hydroxyproline which are important in protein structure. Therefore, comparatively lower temperatures are required for thermal shrinkage and denaturation of collagen in fish (Harrington & von Hippel, 1961). Because of the low content of connective tissue in fish coupled with the low thermal stability of collagen, the textural properties of fish are dependent predominantly on the state of the myofibrillar proteins (Dunajski, 1979). During cooking, as the temperature increases, the myofibrils become tougher while the collagen becomes softer. Collagen fibers become solubilised at 60 C and loose their original structure, this causes a total loss of binding properties of the connective tissue. Above 60 C, heat denaturation of myofibrillar proteins causes the textural changes. However, during cooking the forces acting between the muscle fibers and the myofibrils become weak and the muscles fall apart very easily giving cooked fish a flaky appearance (Dunajski, 1979). Therefore, the muscle fibers become the only form of resistance in cooked fish. The tooth probe was thus positioned to measure the resistance of the muscle fibers. The reason why the cooked King Salmon samples had firmer textures than the raw King Salmon (Table 4) was in part due to myofibrillar toughening during heating. This was also observed in a study by Bhattacharya, Choudhury, and Studebaker (1993) where texture hardness increased with temperature and time. In the current study, the steamed King Salmon had the softest texture among all the cooking methods although this was not statistically significant (p < 0.05) compared to the other cooking methods. Whereas the deep fried King Salmon had the firmest texture, followed by pan fried. It was observed that the deep fried and pan fried samples formed a ‘crust’ on the surface of the fish. Even though the pan frying was conducted without oil (and sometimes referred to as roasting), a ‘crust’ was still visible although not as uniform or thick as the deep fried ‘crust’. The deep fried crust most likely formed due to dehydration in the outer layers of the fish and when the oil was absorbed into the fish caused the visible dry crisp crust on its surface. Deep frying increased the texture of King Salmon 3.6 times more than the raw fish. The pan frying process increased the texture of King Salmon 2.8 times more than the raw fish (Table 4). The crust was formed in the pan fried samples predominantly due to dehydration on the surface of the fish due to high temperatures on the cooking surface. The instrumental texture measurements (Table 4) were linked with the texture hardness data collected from the sensory evaluation (Fig 2). The cohesiveness which is the measure of the force required to break apart the fish muscle (Bhattacharya et al., 1993) did not significantly (p > 0.05) change between the methods (Table 4). A study by Bhattacharya et al. (1993) observed that cohesiveness increased during initial heating of chum King Salmon (in a water bath) and then becoming constant and was not affected greatly by the processing temperature. The springiness, which measures the degree of quickness of recovery when the compressive force is removed from the sample significantly (p < 0.05) increased in pan fried and deep fried King Salmon samples compared to the raw (Table 4). This was also observed in the study by Bhattacharya et al. (1993) where raw Chum Salmon had poor springiness but as the temperature increased during initial heating at 60 and 70 C, the springiness also increased. However, with prolonged heating at 90 C and 100 C, the springiness decreased. Cheng, Hamann, and Webb (1979) also found that minced Gray trout and Atlantic Croaker had a more springy texture when heated to 85 C. Chewiness is the length of time to masticate the fish to a consistency which is appropriate for swallowing at a constant rate of force application. The raw, steamed and poached King Salmon
1818
D. Larsen et al. / LWT - Food Science and Technology 44 (2011) 1814e1820
Fig. 2. PCA of sensory texture and instrumental texture measurements combined across the six cooking methods. PO ¼ poached, OB ¼ oven baked, PF ¼ pan fried, MW ¼ microwaved, DF ¼ deep fried, ST ¼ steamed, and DOL ¼ degree of liking.
had the lowest chewiness (Table 4). Microwaved and oven baked King Salmon had comparable chewiness. Deep fried King Salmon was the most chewy followed by pan fried King Salmon. This was also observed by Bhattacharya et al. (1993) where the raw Chum Salmon had the lowest chewiness. They also observed the chewiness of the fish increased at 60e100 C during initial heating but decreased at 80e100 C after prolonged heating. 3.3. Sensory evaluation The matrix of mean ratings for the attributes of texture (both instrumental and texture hardness, texture DOL and overall DOL from the sensory evaluation) across the six different cooking methods were analysed by Principal Component Analysis (Fig. 2). The first two principal components (PC’s) were responsible for 99% and 1% of the variance, respectively. The oven baked sample is closely linked in the PC space to the texture DOL and indeed the overall DOL. This was expected as the texture DOL of the oven baked King Salmon was rated most highly in the sensory evaluation and the ANOVA of the results of overall DOL showed that oven baked and pan fried King Salmon were liked significantly more than the least liked method, poached King Salmon (Table 5). Also there were positively significant correlations between the aroma DOL and flavour DOL of oven baked King Salmon and its overall DOL (Table 3). Pan fried King Salmon which had the second highest rated texture DOL and overall DOL was also linked to these in the PC space. Fig. 2 shows there was no relation between poached King Salmon and the texture DOL or overall DOL in the PC space and was also the least favoured cooking method from the sensory evaluation (Table 5). Deep fried King Salmon also showed no relation between the texture DOL and the overall DOL in the PC space but did show a significantly positive correlation between the texture DOL and the overall DOL (Table 3). This is most likely due to the influence of the instrumental texture measurements in the PC space as these have a heavy weighting on the deep fried King Salmon as the instrumental texture measurements showed a much harder texture and
it was significantly more springy and chewy than the other cooking methods (Table 4). From the sensory texture evaluation, it was clear that the cooking methods that were rated as the most intense and the least intense, deep frying and poaching, respectively, were both the least liked (Table 2). Whereas, a method such as oven baking that was perceived as middle range in colour, aroma and texture intensities was well accepted by the sensory panel. The oven baked King Salmon did rate as the second most intense flavour after deep fried, and had the most significant positive correlation between the flavour DOL and the overall DOL (Table 3). This suggests there is a possibility that flavour is the most important attribute when determining DOL of the King Salmon as the data collected from the panellists in the sensory evaluation also ranked flavour as the most important sensory attribute in fish, followed by texture, colour and aroma. This is supported by the evidence that all the cooking methods showed significant positive correlations between their flavour DOL and texture DOL and the corresponding overall DOL (Table 3). The flavour DOL and texture DOL, however, both showed no significant differences among the different cooking methods. There were similarities between some of the cooking methods, as they were consistently correlated with the intensity ratings of some sensory attributes. These include correlations between the flavour and colour intensities and DOL of steamed, poached and microwaved King Salmon (Table 2). Poached and microwaved king salmon were both not liked. Poached samples in particular were rated the least intense in flavour, texture, aroma and colour, had the lowest DOL for all attributes including overall DOL. Instrumental colour measurement also showed that the poached King Salmon had the largest increase in lightness (Table 1). The colour of King Salmon flesh is extremely important as consumers expect a certain degree of redness that is indicative of King Salmon. Therefore, it was unexpected that colour was only ranked as the third most important attribute by the panel in the initial questionnaire. Correlation between instrumental colour measurements and the sensory evaluation was not possible as only colour intensity was tested in the sensory evaluation. However, the trend showed that the cooking methods which became lighter such as poaching and steaming
D. Larsen et al. / LWT - Food Science and Technology 44 (2011) 1814e1820
1819
Table 2 Correlations between the texture, flavour, aroma and colour intensity and DOL of cooked New Zealand King Salmon from the sensory evaluation. DOL Property
Intensity
PO
OB
PF
Texture
PO OB PF MW DF ST
0.433** 0.109 0.147 0.169 0.014 0.252
0.115 0.043 0.032 0.245 0.031 0.255
0.247 0.209 0.266 0.077 0.045 0.096
Flavour
PO OB PF MW DF ST
0.628** 0.164 0.099 0.404* 0.079 0.527**
0.178 0.165 0.113 0.161 0.035 0.06
0.138 0.152 0.275 0.378* 0.331* 0.383*
Aroma
PO OB PF MW DF ST
0.126 0.082 0.214 0.067 0.073 0.267
0.13 0.338* 0.085 0.037 0.036 0.089
Colour
PO OB PF MW DF ST
0.660** 0.27 0.218 0.253 0.287 0.248
0.199 0.679** 0.004 0.048 0.18 0.08
MW
DF
ST
0.165 0.087 0.118 0.071 0.318* 0.131
0.331* 0.254 0.122 0.054 0.079 0.109
0.321* 0.166 0.174 0.370* 0.238 0.392*
0.007 0.107 0.165 0.119 0.329* 0.207
0.653** 0.254 0.051 0.328* 0.008 0.403*
0.072 0.051 0.370* 0.016 0.237 0.118
0.057 0 0.031 0.105 0.108 0.222
0.114 0.295 0.319* 0.118 0.086 0.029
0.294 0.057 0.02 0.054 0.176 0.408**
0.16 0.257 0.21 0.116 0.605** 0.165
0.115 0.177 0.231 0.555** 0.188 0.298
0.247 0.258 0.424** 0.152 0.173 0.126
0.136 0.095 0.165 0.235 0.269 0.499**
0.072 0.359* 0.034 0.407** 0.064 0.064
Key: PO ¼ poached, OB ¼ oven baked, PF ¼ pan fried, MW ¼ microwaved, DF ¼ deep fried, ST ¼ steamed, and DOL ¼ degree of liking. ** Correlation is significant p < 0.01 (two-tailed). * Correlation is significant p < 0.05 (two-tailed). Fifty replicates per measurement.
(Table 1) were rated significantly less intense according to the sensory evaluation and these methods in turn were the least liked (although this was only significantly different compared with microwaved, pan fried and poached). This suggests that once King Table 3 Correlations between the texture, flavour, aroma and colour DOL and overall DOL of cooked New Zealand King Salmon from the sensory evaluation. Overall DOL Property DOL PO
OB
PF
MW
DF
ST
Texture
0.106 0.312* 0.145 0.395* PO 0.815** 0.017 OB 0.139 0.803** 0.002 0.025 0.052 0.227 0.09 0.075 PF 0.117 0.055 0.473** 0.381* MW 0.307 0.046 0.057 0.569** 0.012 0.099 ** 0.024 DF 0.094 0.037 0.275 0.128 0.691 * 0.039 0.104 0.192 0.266 0.701** ST 0.354
Flavour
PO 0.755** OB 0.046 PF 0.105 MW 0.173 DF 0.086 ST 0.367*
Aroma
PO 0.524** 0.178 0.114 OB 0.185 0.478** 0.203 PF 0.013 0.148 0.386* MW 0.042 0.266 0.062 DF 0.114 0.043 0.149 ST 0.117 0.305 0.016
Colour
0.07 0.830** 0.138 0.021 0.101 0.141
PO 0.299 0.162 OB 0.104 0.136 PF 0.264 0.026 MW 0.446** 0.212 DF 0.072 0.243 ST 0.143 0.005
0.005 0.227 0 0.344* 0.287 0.185 0.225 0.265 0.206 0.272 0.518** 0.155 0.193 0.15 0.553** 0.16 ** 0.182 0.004 0.176 0.769 0.136 0.328* 0.329* 0.653** 0.07 0.18 0.015 0.178 0.139 0.03
0.062 0.198 0.093 0.111 ** 0.242 0.583 0.400* 0.384* 0.204 0.249 0.025 0.295
0.182 0.529** 0.410** 0.172 0.052 0.113 0.016 0.035 0.199 0.463** 0.015 0.173 0.095 0.099 0.342* 0.209 0.388* 0.113
0.068 0.057 0.374* 0.540** 0.285 0.087
Key: PO ¼ poached, OB ¼ oven baked, PF ¼ pan fried, MW ¼ microwaved, DF ¼ deep fried, STt ¼ steamed, and DOL ¼ degree of liking. ** Correlation is significant p < 0.01 (two-tailed). * Correlation is significant p < 0.05 (two-tailed). Fifty replicates per measurement.
Salmon looses its ‘redness’ as it did during poaching and steaming, it becomes less desirable to the consumer. Whereas deep fried King Salmon had a significantly greater red colour (highest a* value) (Table 1) and was also rated as most intense. It had a significantly positive correlation between the colour DOL and overall DOL. The colour DOL of pan fried and microwaved was also correlated to their overall DOL (Table 3). This correlation indicated that liking or disliking the colour may have influenced how much the panellists liked or disliked the King Salmon sample overall. However, as with all these findings, it is important to state that correlation does not necessarily imply causation. Aroma was ranked the least important attribute of fish in the initial questionnaire. Generally, aroma is one of the most important properties of fish as it is a good indicator of freshness. The results showed that the methods that produced more intense aromas were more liked, such as deep fried and pan fried King Salmon; and the poached King Salmon had the least intense aroma and was liked the least. However, the oven baked King Salmon was most liked, although was rated to have a mid range intensity. The aroma DOL of poached, oven baked, pan fried and deep fried King Salmon and their corresponding overall DOL’s were correlated (Table 3).
Table 4 Instrumental texture measurements of raw and cooked New Zealand King Salmon. Cooking method
Hardness (N)
Cohesiveness
Springiness (mm)
Chewiness (N mm)
Raw Poached Steamed Microwaved Oven baked Pan fried Deep fried
0.70 0.1a 0.99 0.2a 0.93 0.2a 1.45 0.15a 1.21 0.3a 1.93 0.3a 2.52 0.2a
0.60 0.06a 0.65 0.08a 0.60 0.04a 0.62 0.05a 0.57 0.05a 0.67 0.08a 0.60 0.03a
0.22 0.01a 0.21 0.03a 0.22 0.02a 0.25 0.01a 0.27 0.01a 0.36 0.01a,b 0.52 0.01c
0.24 0.06a 0.27 0.02a 0.27 0.01a 0.43 0a 0.43 0.03a 0.84 0.1a,b 1.28 0.1c
Different letters in the same column indicate significant differences (p < 0.05). Twenty-seven replicates per measurement.
1820
D. Larsen et al. / LWT - Food Science and Technology 44 (2011) 1814e1820
Table 5 Mean sensory evaluation ratings on a 10 cm line scale of individual sensory attributes and DOL. Cooking method
PO ST MW OB PF DF
Colour
Aroma
Flavour
Texture
Overall DOL
Intensity
DOL
Intensity
DOL
Intensity
DOL
Intensity
DOL
2.79a 3.06a 4.27b 6.10c 7.58d 8.07d
3.53a,b 4.17b,e 5.33a,c,e 6.92b,c 6.13c,d 6.26d
3.26a 4.27a,c 4.63a,c 5.41b 6.50b,d 7.24d
3.99a,b 4.85b 4.33a,b 6.30c,b 6.02c,b,d 6.30c,b,d
4.19a 5.16b 5.49c 5.95a 5.39d 5.94a
4.65a 5.49a 4.79a 6.14a 5.70a 5.21a
2.93a 3.41a,c 3.28a,c 4.69b 5.85b 7.53d
4.56a 5.38a 5.16a 5.91a 5.83a 4.96a
4.29a,c 5.52b,c 4.94b,c 6.36b 6.18b 4.83b,c
Key: PO ¼ poached, OB ¼ oven baked, PF ¼ pan fried, MW ¼ microwaved, DF ¼ deep fried, ST ¼ steamed, and DOL ¼ degree of liking. Different letters in the same column indicate significant differences (p < 0.05). Fifty replicates per measurement.
Interestingly, the sensory data was correlated with a study investigating the effect that the same cooking methods had on the fatty acid profile of King Salmon that was run in tandem with the current study (Larsen et al., 2009). It was found that oven baked salmon actually had the highest levels of DHA, EPA and DPA amongst the cooked samples and was liked the most by consumers. This was also found with poached King Salmon which was least liked by the sensory panel and also had the lowest amount of DHA, EPA and DPA. This shows that potentially consumers are inadvertently choosing cooking methods that are actually the best at preserving the omega-3 levels. 4. Conclusions After cooking, the King Salmon became lighter, more red and more yellow as seen by instrumental colour analysis. Instrumental texture measurements showed an increase in the texture hardness and chewiness of King Salmon with cooking. The instrumental texture measurements were closely linked with sensory texture hardness and both texture DOL and flavour DOL showed significant positive correlations with their overall DOL for each cooking method. Overall oven baked and pan fried King Salmon were the methods with the highest DOL and were liked significantly more than the least liked cooking method, poaching. Acknowledgements We thank The New Zealand King Salmon Company and The National Foundation for Research Science and Technology, for providing funding for this study. References AOAC. (1999). Official methods of analysis of AOAC International. In W. Horwitz (Ed.) (16th ed.). Arlington, VA, USA: AOAC International. Bhattacharya, S., Choudhury, G. S., & Studebaker, S. (1993). Hydrothermal processing of Pacific Chum Salmon: effects on texture and in-vitro digestibility. Journal of Food Quality, 16, 243e251.
Birch, E. E., Hoffman, D. R., Uauy, R., Birch, D. G., & Prestidge, C. (1998). Visual acuity and the essentiality of docosahexaenoic acid and arachidonic acid in the diet of term infants. Pediatric Research, 44, 201e209. Cheng, C. S., Hamann, D. D., & Webb, N. B. (1979). Effect of thermal processing on minced fish gel structure. Journal of Food Science, 44, 1080e1986. Colangelo, L. A., He, K., Whooley, M. A., Daviglus, M. L., & Liu, K. (2009). Higher dietary intake of long-chain u-3 p.lyunsaturated fatty acids is inversely associated with depressive symptoms in women. Nutrition, 25(10), 1011e1019. Darlington, L. G., & Stone, T. W. (2001). Antioxidants and fatty acids in the amelioration of rheumatoid arthritis and related disorders. British Journal of Nutrition, 85, 251e269. Dunajski, E. (1979). Texture in fish muscle. Journal of Textural Studies, 10, 301e318. Erkkila, A. T., Lichtenstein, A. H., Mozaffarian, D., & Herrington, D. M. (2004). Fish intake is associated with a reduced progression of coronary artery atherosclerosis in postmenopausal women with coronary artery disease. American Journal of Clinical Nutrition, 80, 626e632. Foss, P., Storebakken, T., Schiedt, K., Liaaen-Jensen, S., Austreng, E., & Strieff, K. (1984). Carotenoids in diets of Salmonids. Aquaculture, 41, 213e226. He, K., Song, Y., Daviglus, M. L., Liu, K., Van Horn, L., Dyer, A. R., et al. (2004). Accumulated evidence on fish consumption and coronary heart disease mortality: a meta-analysis of cohort studies. Circulation, 109, 2705e2711. He, K., Liu, K., Daviglus, M. L., Jenny, N. S., Mayer-Davis, E., Jiang, R., et al. (2009). Associations of dietary long-chain n-3 p.lyunsaturated fatty acids and fish with biomarkers of inflammation and endothelial activation (from the Multi-Ethnic Study of Atherosclerosis [MESA]). The American Journal of Cardiology, 103, 1238e1243. Harrington, W. F., & von Hippel, P. H. (1961). The structure of collagen and gelatin. Advanced Protein Chemistry, 16, 1e138. Hutchings, J. B. (1999). Food colour and appearance (2nd ed.). Maryland, U.S.A.: Aspen publishers, Incorporated. pp. 347e348, 351, 512e513, 535. Krutulyte, R., Grunert, K. G., Scholderer, J., Skov Hagemann, K., Elgaard, P., Nielsen, B., et al. (2008). Motivational factors for consuming omega-3 PUFAs: an exploratory study with Danish consumers. Appetite, 51, 137e147. Larsen, D. S., Quek, S. Y., & Eyres, L. (2009). Effect of cooking method on the fatty acid profile of New Zealand King Salmon (Oncorhynchus tshawytscha). Journal of Food Chemistry., 119(2), 785e790. Pokorny, J. (1981). Browning from lipid-protein interactions. Progress in Food and Nutrition Science, 5, 421e428. Sigurgisladottir, S., Hafsteinsson, H., Jonsson, A., Lie, O., Nortvedt, R., Thomassen, M., et al. (1999). Textural properties of raw Salmon fillets as related to sampling method. Journal of Food Science, 64(1), 99e104. Skrede, G., & Storebakken, T. (1986). Characteristics of colour, in raw, baked and smoked wild and pen-reared Atlantic Salmon. Journal of Food Science, 51, 804e808. Szczesniak, A. S. (1963). Classification of textural characteristics. Journal of Food Science, 28, 385e389. Trondsen, T., Scholderer, J., Lund, E., & Eggen, A. E. (2003). Perceived barriers to consumption of fish among Norwegian women. Appetite, 41, 301e314. Verbeke, W., & Vackier, I. (2005). Individual determinants of fish consumption: application of the theory of planned behaviour. Appetite, 44, 67e82.
Contents lists available at ScienceDirect
LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt
Evaluating instrumental colour and texture of thermally treated New Zealand King Salmon (Oncorhynchus tshawytscha) and their relation to sensory properties Danaé Larsen, Siew-Young Quek*, Laurence Eyres Food Science Programme, Department of Chemistry, The University of Auckland, 23 Symonds Street, Auckland, New Zealand
a r t i c l e i n f o
a b s t r a c t
Article history: Received 1 March 2010 Received in revised form 15 March 2011 Accepted 16 March 2011
Farmed New Zealand King Salmon (Oncorhynchus tshawytscha) was prepared according to common consumer techniques, namely poached, steamed, microwaved, pan fried (no oil), oven baked (no oil) and deep fried (in sunflower oil). Colour and texture were measured instrumentally and a sensory evaluation comprising of a generic QDA was conducted for the intensity and overall liking of the properties of colour, texture, flavour and aroma. During the thermal treatment (cooking), the outer colour of the King Salmon fillets became lighter, more red and yellow. Thermal treatment increased the texture firmness, chewiness and springiness of King Salmon as measured by texture analyser. Overall, the sensory panel preferred the oven baked King Salmon but least liked the poached and microwaved King Salmon. The instrumental texture measurements of the cooked King Salmon were closely linked with the texture ratings from the sensory panel. These experiments provide useful data for determining the optimal preparation techniques that in turn can facilitate the farming of NZ King Salmon to directly benefit the consumer. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: King Salmon Sensory properties Colour Texture
1. Introduction Consumers are becoming increasingly aware of the beneficial effects of including long chain polyunsaturated fatty acids (LCPUFA) in the diet. There have been several studies showing the positive effect that LCPUFA, in particular the omega-3 fatty acids (n-3 FA), EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) has on a range of health problems. An increased intake of LCPUFA has shown to have beneficial effects on atherosclerosis progression (Erkkila, Lichtenstein, Mozaffarian, & Herrington, 2004) and protecting against cardiovascular disease (He et al., 2004). Several epidemiological studies have also shown favourable effects on inflammation and endothelial function (He et al., 2009), with studies also showing the therapeutic benefit of LCPUFA in rheumatoid Arthritis treatment (Darlington & Stone, 2001). LCPUFA are also beneficial in promoting infant brain development and eye function (Birch, Hoffman, Uauy, Birch, & Prestidge, 1998) and have been found to be inversely associated with chronic depression symptoms in women (Colangelo, He, Whooley, Daviglus, & Liu, 2009). Humans cannot synthesise n-3 FA, instead they have to obtain n-3 fatty acids from those that pass through the food chain and
* Corresponding author. Tel.: þ64 9 3737599x85852; fax: þ64 9 373 7422. E-mail address: [email protected] (S.-Y. Quek). 0023-6438/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2011.03.018
become incorporated in fish and marine mammals. A good source of n-3 fatty acids is from oily fish, in particular the Salmon species. Even though there is an increased consumer awareness of increasing the intake of fatty fish, such as Salmon in the diet, many people in Western countries are still not eating the recommended level (Krutulyte et al., 2008). Previous studies by Trondsen, Scholderer, Lund, and Eggen (2003) and Verbeke and Vackier (2005) revealed that the perceived time-consuming nature of preparing fish and the sensory properties, most notably taste, are the predominant contributors to why consumers are reluctant to increase their fatty fish intake even though the health benefits are now widely known. In New Zealand, King Salmon is generally consumed in a cooked state. Previous research on the effect of cooking method on the LCPUFA levels in King Salmon was undertaken by Larsen, Quek & Eyres (2010) and it was found that regardless of cooking method, NZ King Salmon is a good source of LCPUFA. However, to get consumers to include more LCPUFA in their diets, it is important to understand the effect that different preparation techniques have on the sensory properties of the salmon as sensory properties play a vital role in consumption choices. The sensory parameters that are important in determining the consumption of fish include colour, texture, flavour and aroma (Sigurgisladottir et al., 1999). The objective of this research was to study the effect of different heat treatment (cooking) methods on the key sensory properties in
D. Larsen et al. / LWT - Food Science and Technology 44 (2011) 1814e1820
NZ King Salmon using instrumental colour and texture measurements and a sensory evaluation to obtain an idea on the optimal preparation techniques to fulfil consumer satisfaction.
2. Materials and methods 2.1. Materials and sample preparation Fresh King Salmon was supplied by the New Zealand King Salmon Company, Nelson, New Zealand. All fish was transported to the laboratory chilled. The King Salmon was obtained as fillets without skin (MayeAugust, 2007). All samples were taken from the same sample area (Fig. 1). Each measurement conducted was taken from 9 separate fish with each individual fish sampled in triplicate. One hundred gram samples of Salmon were cooked from fresh, following AOAC 976.16 (method for cooking seafood) (AOAC, 1999), where the Salmon reached an internal temperature of 70 C for each cooking method. A sample size of 27 was used for each cooking method. Different heat treatments were selected as common cooking procedures used by consumers. These were poaching, steaming, microwaving, pan frying, oven baking and deep frying. All these methods were undertaken without the addition of salt or oil apart from deep frying which used sunflower oil. Poaching e the King Salmon samples were placed in a stainless steel pot of boiling water (500 mL) with the lid on for 3 min and 30 s. After this, the samples were removed and drained on absorbent paper towels. Pan frying e the King Salmon samples were positioned in a nonstick frying pan (180 C) bone side down for 3 min, then skin side down for 3 min. Each short side was then cooked for 1 min. Total cooking time per sample was 8 min. The cooking temperature was monitored with a digital probe. After cooking, the pan was wiped with pre-weighed absorbent paper towels to obtain the weight of excess oil exuded during cooking. Microwaving e the King Salmon samples were individually placed on a pre-weighed ceramic plate and cooked on full power for 40 s (Panasonic Genius, Japan). The samples were then placed on pre-weighed absorbent paper towels. Oven baking e the King Salmon samples were put in a preweighed Teflon lined stainless steel baking dish and cooked in a convection oven at 180 C for 10 min. The samples were then removed and the excess oil absorbed onto pre-weighed paper towels which were weighed to obtain the weight of excess oil exuded during cooking. Steaming e the King Salmon samples were placed in a stainless steel steamer above a stainless steel pot of boiling water (500 mL)
Fig. 1. Sampling location on King Salmon fillet.
1815
with the lid on for 5 min and 30 s. After this, the King Salmon samples were placed on absorbent paper towels. Deep frying e the King Salmon samples were placed in a wire mesh basket and immersed in sunflower oil in a deep fryer (Sanyo easy clean, Japan) for 5 min at 180 C. After frying, the basket was shaken and the samples placed on absorbent paper towels. After each of the heat treatments, the samples were cooled to room temperature and weighed to obtain the cooked % yield, colour and texture were then measured. 2.2. Analytical procedures 2.2.1. Colour Instrumental colour analyses of the King Salmon fillets were conducted using a CR300 colourimeter (Minolta, Osaka, Japan). Measurements were made directly on the fillet, where L* value describes lightness, a* value redness and b* value yellowness as recommended by CIE 1976 (Commission Internationale de l’Eclairage, Vienna, Austria). Instrumental colour measurements were taken on the surface of each side of the fillet sample (“outer fillet”) as well as on the flesh inside the fillet (“inner fillet”) with triplicate measurements. All colour testing of King Salmon was carried out before and immediately after cooking, once the samples had reached room temperature. 2.2.2. Texture Initially the texture of raw King Salmon was tested to determine texture variation due to anatomical location along the whole fillet. It was found that the locations near the tail end (approximately 10 cm from end of tail) were significantly softer than the locations near the head or in the centre. This was also observed in the study by Sigurgisladottir et al. (1999) which observed that sampling locations closer to the tail of the fish were more sensitive to breaking than those from the head sections. This is probably due to differences in musculature throughout the fish flesh and therefore variations within individuals exist according to anatomical location. In the current study, all samples were taken from the central region of the fillets where there was no significant difference in texture prior to cooking. The raw and cooked fillet portions were cooled to room temperature (19 1 C). A smaller sample section was cut from each fillet portion (3 cm 3 cm 3 cm). A TA.XT2 Texture Analyser (Stable Micro System, Surrey, England) with two different probe attachments were used; a spherical probe to specifically assess the compression of the Salmon flesh and a tooth probe to mimic the human bite as it shears the Salmon flesh. Double compression was applied to construct the texture profile analyses (TPA) parameters following the method modified from Sigurgisladottir et al. (1999). The spherical probe (25 mm diameter) approached the sample at a pre test speed of 2 mm/s and then penetrated 5 mm into the fillet at a test speed of 2 mm/s. The fillet was then allowed to rebound for 15 s by reducing the force of the sphere so that it just touched the surface of the fillet. The sphere was then pressed onto the fillet again resulting in a double compression. The sphere then returned to its starting position at a post-test speed of 2 mm/s. The tooth probe (10 mm) was positioned perpendicular to the muscle fibers in the samples. The tooth probe approached the sample at a pre test speed of 2 mm/s and then penetrated 5 mm into the fillet at a test speed of 2 mm/s. The probe then returned to its starting position at a post-test speed of 2 mm/s. Each texture measurement was conducted in triplicate. Cohesiveness and springiness were measured from the TPA and chewiness was calculated as a product of hardness, springiness and cohesiveness.
1816
D. Larsen et al. / LWT - Food Science and Technology 44 (2011) 1814e1820
2.3. Sensory evaluation
2.4. Statistical analysis
A sensory evaluation was conducted by recruiting 50 nontrained participants. The participants ranged in age from 19 to 50 years, 18 male, 32 female, and were from various ethnic groups. The participants fish consumption habits ranged from less than once per month to at least 3 times per week, and their salmon consumption ranged from less than once per month to once per week. The sensory evaluation was carried out in specialised sensory booths. The evaluation area had a controlled environment, which was noise and distraction free and ensured conditions remained the same throughout the trials. A hatch system was utilised in which the samples were passed from the preparation area to the panellists, so they could not visibly see the preparation area. Each booth was equipped with a score sheet, pen, a spittoon, serviettes, a glass of clear apple juice and a glass of filtered water with unlimited supply. The score sheet had instructions for the panellists to follow which reiterated those verbally given at the beginning of the session. Panellists were instructed to rinse their mouths with apple juice and then water between samples and to expectorate into the spittoon if required. The presentation of samples was randomised and panellists always sampled from left to right and were allowed to resample during the trial if required. Detailed instructions complete with an example on how to mark the score sheet to indicate their response were included on the score sheet. Cooked King Salmon was sampled during the sensory evaluation. The King Salmon was cooked immediately before each session. After cooking, the King Salmon was cut into w25 g pieces and served at 30 C. In total six samples, one from each different cooking method was tested. The Salmon samples were given to each panellist individually to maintain a constant temperature between samples. Each cooking method was assigned a randomly generated three digit number as a reference code so that the panellists did not know the difference between samples. Panellists were asked to indicate on a 10 cm line scale how they perceived the colour intensity, flavour intensity, aroma intensity, and texture. The endpoints for each scale were “extremely soft” and “extremely hard” for texture, “extremely light” and “extremely dark” for colour intensity, “extremely weak” and “extremely strong” for aroma and flavour intensity. They were also asked to indicate how much they liked or disliked each of these components on a 10 cm line scale with the endpoints “extremely dislike “ and “extremely like”. The overall opinion of each sample was also collected using the same 10 cm line scale. The panellists were also asked to rank (from 1 to 4, with 1 being most important) their order of importance for the four key sensory properties; taste, aroma, colour and texture when they consume Salmon.
One way analysis of variance (ANOVA) and bivariate correlations were conducted using SPSS 17.0, SPSS Inc. IL, USA and a significance level of p < 0.05 was used. Principal component analysis (PCA) was conducted on the instrumental texture data and the texture data from the sensory evaluation using The UnscamblerÒ software package, v9.7, Camo Software, Norway. 3. Results and discussion 3.1. Instrumental colour analysis Comparing the inner and outer colour of raw and cooked King Salmon showed that for all methods the cooked fillets were lighter, more red and more yellow as reflected by increases in L*, a* and b* values, respectively (Table 1). Of the outer fillets of the cooked King Salmon, the deep fried and pan fried King Salmon had the lowest L* value and high a* values, indicating these methods produced samples with the darkest colour. The oven baked King Salmon had the highest b* value followed by the pan fried and oven baked King Salmon. This showed that the above methods produced samples with a more yellow colour. On the other hand, the poached King Salmon had the highest L* value and also the lowest a* and b* values, reflecting the lightest colour among the cooking methods. For the inner fillets, the deep fried and oven baked King Salmon had the highest L* values, followed by the pan fried King Salmon. The poached and microwaved King Salmon had the lowest L* values. Conversely, the poached King Salmon had the highest a* and b* values while the microwaved King Salmon had the lowest although, there was a very small difference in the red and yellow colour of the inner fillet between cooking methods. Processing affects the colour of a product through changes in the nature of the pigment or its content and/or physical state (Hutchings, 1999). During cooking of fish, the addition of heat causes protein aggregation. Opacity increases consequently causing the lightness value (L* value) to increase. The optical path length in the flesh is reduced due to the increase in opacity and as a result, the light that enters the surface has a lower chance of being selectively absorbed. This causes a drop in the perceived redness (a* value) as noted by Skrede and Storebakken (1986) in their study on Atlantic Salmon. However, the a* values did not decrease as expected, instead all the a* values for the inside and outer surface of the King Salmon samples increased on cooking, with a significant difference between raw and deep fried King Salmon (p < 0.05). There was a greater increase in redness of the outer flesh colour as expected, due to surface browning during some of the cooking methods, especially deep fried and pan fried, but unexpectedly this also occurred also in the microwaved King Salmon although there was
Table 1 Instrumental mean measurements of the inner and outer fillet colours of raw and cooked New Zealand King Salmon. Cooking method
Raw Microwaved Pan fried Poached Steamed Oven baked Deep fried
Outer fillet colour
Inner fillet colour
L*
a*
b*
L*
a*
b*
47.88 3.61a 69.01 3.17b,c,d 57.46 3.61e 73.91 2.89b,f,g 72.61 1.69c,f,h 70.13 2.94d,g,h 56.27 3.82a,e
15.88 0.76a 22.68 3.60b 22.42 2.29b 19.65 2.43b 18.78 2.36b 21.13 4.15b 24.75 1.87c
16.89 1.13a 27.04 3.22b 29.12 4.25b 25.82 3.09b 25.05 3.23b 30.19 3.87b 26.56 5.13b
51.98 1.36a 66.88 3.11b,c 74.19 2.27b,d 67.47 0.23b,c 72.51 3.81b 75.38 1.39b,d 75.05 2.90b,d
19.39 0.54a 20.53 1.07a 21.58 2.94a 22.66 5.21a 22.04 3.63a 20.72 2.89a 21.48 2.71a
21.52 0.7a 22.53 1.25a 23.42 2.77a 25.15 5.43a 23.59 3.89a 23.04 2.31a 23.83 4.4a
Different letters in the same column indicate significant differences (p < 0.05). Twenty-seven replicates per measurement.
D. Larsen et al. / LWT - Food Science and Technology 44 (2011) 1814e1820
no visible browning on the outer surface. The King Salmon in the current research has a diet supplemented with astaxanthin instead of canthaxanthin, which is less red. In a lot of the literature on farmed salmon, canthaxanthin is the most common supplement, therefore the change in redness may be due to the initial redness from the astaxanthin. The utilisation of carotenoids by salmon is improved with high dietary lipid content (Foss, Storebakken, Schiedt, Liaaen-Jensen, Austreng & Strieff, 1984). The desired redness in salmon is enhanced in fish with higher oil content because there is a greater refractive index between muscle and air than between muscle and oil (Foss et al., 1984). This means that there is less light scattering and more redness. Fish with lower oil content leads to increased light scattering and therefore lower the redness. However, this did not occur in the cooked King Salmon, probably because there are other changes that occurred during cooking as well as the changes in redness. Also, the differences in a* value between the methods may not have been large enough to show a trend with their lipid content. Only the deep fried samples were the most red and had the highest lipid content (data not shown) but this was probably due to the absorption of sunflower oil during frying than the lipid content affecting the redness. The intake of pigments and oil in the diet of King Salmon varies with season and the environment and therefore varies in the flesh. More so in the wild, this leads to different associations between carotenoid determination and visual redness. Farmed King Salmon are feed specific diets that are high in carotenoids and oil to enhance the redness of the fish and this generally causes less seasonal changes. Deep frying caused the largest difference in colour for the King Salmon. The deep fried King Salmon, however, was more red but not as yellow as some of the other samples. Possibly this was because King Salmon flesh was already quite a dark orange red and therefore, the effect of deep frying was not as pronounced as it would be in white fleshed fish. The most browning was observed in the deep fried, pan fried and oven baked King Salmon. This was most likely caused by the Maillard reactions which are caused by non-enzymic browning. The reducing sugars and free amino acids react forming colourless premelanoidins which undergo polymerisation into macromolecular melanoidins which are deep brown in colour. Also similar browning reactions are caused through oxidation products in the frying oil such as hydroperoxides or unsaturated aldehydes interacting with the free amine group of bound lysine (Pokorny, 1981). 3.2. Instrumental texture analysis Fish flesh is rheologically and structurally complex and consists of a combination of solid and fluid components (Dunajski, 1979). The properties and concentrations of the structural elements in the fish tissue and their arrangements in the muscle influence the textural properties and mouth feel (Szczesniak, 1963). The textural properties of the muscle tissue such as firmness or toughness are directed by the fibourous proteins, which are present as 70e80% of the total protein content (Dunajski, 1979). The effect on the texture due to these two types of proteins, myofibrillar proteins (present inside muscle fibers) and constituents of the connective tissue are governed by ante mortem and post-mortem factors and also by the type of processing (Dunajski, 1979). Because of the flakiness of cooked fish, measuring the texture with instruments is difficult. The positioning of the samples becomes crucial. To conduct Texture Profile Analysis (TPA), a sphere probe was used to try to get a representative analysis of the whole cooked sample. This was hindered by the weak forces of attraction between the myofibrils and between the fibers.
1817
Fish collagen is less thermally stable and more soluble than mammalian collagen as it contains less proline and hydroxyproline which are important in protein structure. Therefore, comparatively lower temperatures are required for thermal shrinkage and denaturation of collagen in fish (Harrington & von Hippel, 1961). Because of the low content of connective tissue in fish coupled with the low thermal stability of collagen, the textural properties of fish are dependent predominantly on the state of the myofibrillar proteins (Dunajski, 1979). During cooking, as the temperature increases, the myofibrils become tougher while the collagen becomes softer. Collagen fibers become solubilised at 60 C and loose their original structure, this causes a total loss of binding properties of the connective tissue. Above 60 C, heat denaturation of myofibrillar proteins causes the textural changes. However, during cooking the forces acting between the muscle fibers and the myofibrils become weak and the muscles fall apart very easily giving cooked fish a flaky appearance (Dunajski, 1979). Therefore, the muscle fibers become the only form of resistance in cooked fish. The tooth probe was thus positioned to measure the resistance of the muscle fibers. The reason why the cooked King Salmon samples had firmer textures than the raw King Salmon (Table 4) was in part due to myofibrillar toughening during heating. This was also observed in a study by Bhattacharya, Choudhury, and Studebaker (1993) where texture hardness increased with temperature and time. In the current study, the steamed King Salmon had the softest texture among all the cooking methods although this was not statistically significant (p < 0.05) compared to the other cooking methods. Whereas the deep fried King Salmon had the firmest texture, followed by pan fried. It was observed that the deep fried and pan fried samples formed a ‘crust’ on the surface of the fish. Even though the pan frying was conducted without oil (and sometimes referred to as roasting), a ‘crust’ was still visible although not as uniform or thick as the deep fried ‘crust’. The deep fried crust most likely formed due to dehydration in the outer layers of the fish and when the oil was absorbed into the fish caused the visible dry crisp crust on its surface. Deep frying increased the texture of King Salmon 3.6 times more than the raw fish. The pan frying process increased the texture of King Salmon 2.8 times more than the raw fish (Table 4). The crust was formed in the pan fried samples predominantly due to dehydration on the surface of the fish due to high temperatures on the cooking surface. The instrumental texture measurements (Table 4) were linked with the texture hardness data collected from the sensory evaluation (Fig 2). The cohesiveness which is the measure of the force required to break apart the fish muscle (Bhattacharya et al., 1993) did not significantly (p > 0.05) change between the methods (Table 4). A study by Bhattacharya et al. (1993) observed that cohesiveness increased during initial heating of chum King Salmon (in a water bath) and then becoming constant and was not affected greatly by the processing temperature. The springiness, which measures the degree of quickness of recovery when the compressive force is removed from the sample significantly (p < 0.05) increased in pan fried and deep fried King Salmon samples compared to the raw (Table 4). This was also observed in the study by Bhattacharya et al. (1993) where raw Chum Salmon had poor springiness but as the temperature increased during initial heating at 60 and 70 C, the springiness also increased. However, with prolonged heating at 90 C and 100 C, the springiness decreased. Cheng, Hamann, and Webb (1979) also found that minced Gray trout and Atlantic Croaker had a more springy texture when heated to 85 C. Chewiness is the length of time to masticate the fish to a consistency which is appropriate for swallowing at a constant rate of force application. The raw, steamed and poached King Salmon
1818
D. Larsen et al. / LWT - Food Science and Technology 44 (2011) 1814e1820
Fig. 2. PCA of sensory texture and instrumental texture measurements combined across the six cooking methods. PO ¼ poached, OB ¼ oven baked, PF ¼ pan fried, MW ¼ microwaved, DF ¼ deep fried, ST ¼ steamed, and DOL ¼ degree of liking.
had the lowest chewiness (Table 4). Microwaved and oven baked King Salmon had comparable chewiness. Deep fried King Salmon was the most chewy followed by pan fried King Salmon. This was also observed by Bhattacharya et al. (1993) where the raw Chum Salmon had the lowest chewiness. They also observed the chewiness of the fish increased at 60e100 C during initial heating but decreased at 80e100 C after prolonged heating. 3.3. Sensory evaluation The matrix of mean ratings for the attributes of texture (both instrumental and texture hardness, texture DOL and overall DOL from the sensory evaluation) across the six different cooking methods were analysed by Principal Component Analysis (Fig. 2). The first two principal components (PC’s) were responsible for 99% and 1% of the variance, respectively. The oven baked sample is closely linked in the PC space to the texture DOL and indeed the overall DOL. This was expected as the texture DOL of the oven baked King Salmon was rated most highly in the sensory evaluation and the ANOVA of the results of overall DOL showed that oven baked and pan fried King Salmon were liked significantly more than the least liked method, poached King Salmon (Table 5). Also there were positively significant correlations between the aroma DOL and flavour DOL of oven baked King Salmon and its overall DOL (Table 3). Pan fried King Salmon which had the second highest rated texture DOL and overall DOL was also linked to these in the PC space. Fig. 2 shows there was no relation between poached King Salmon and the texture DOL or overall DOL in the PC space and was also the least favoured cooking method from the sensory evaluation (Table 5). Deep fried King Salmon also showed no relation between the texture DOL and the overall DOL in the PC space but did show a significantly positive correlation between the texture DOL and the overall DOL (Table 3). This is most likely due to the influence of the instrumental texture measurements in the PC space as these have a heavy weighting on the deep fried King Salmon as the instrumental texture measurements showed a much harder texture and
it was significantly more springy and chewy than the other cooking methods (Table 4). From the sensory texture evaluation, it was clear that the cooking methods that were rated as the most intense and the least intense, deep frying and poaching, respectively, were both the least liked (Table 2). Whereas, a method such as oven baking that was perceived as middle range in colour, aroma and texture intensities was well accepted by the sensory panel. The oven baked King Salmon did rate as the second most intense flavour after deep fried, and had the most significant positive correlation between the flavour DOL and the overall DOL (Table 3). This suggests there is a possibility that flavour is the most important attribute when determining DOL of the King Salmon as the data collected from the panellists in the sensory evaluation also ranked flavour as the most important sensory attribute in fish, followed by texture, colour and aroma. This is supported by the evidence that all the cooking methods showed significant positive correlations between their flavour DOL and texture DOL and the corresponding overall DOL (Table 3). The flavour DOL and texture DOL, however, both showed no significant differences among the different cooking methods. There were similarities between some of the cooking methods, as they were consistently correlated with the intensity ratings of some sensory attributes. These include correlations between the flavour and colour intensities and DOL of steamed, poached and microwaved King Salmon (Table 2). Poached and microwaved king salmon were both not liked. Poached samples in particular were rated the least intense in flavour, texture, aroma and colour, had the lowest DOL for all attributes including overall DOL. Instrumental colour measurement also showed that the poached King Salmon had the largest increase in lightness (Table 1). The colour of King Salmon flesh is extremely important as consumers expect a certain degree of redness that is indicative of King Salmon. Therefore, it was unexpected that colour was only ranked as the third most important attribute by the panel in the initial questionnaire. Correlation between instrumental colour measurements and the sensory evaluation was not possible as only colour intensity was tested in the sensory evaluation. However, the trend showed that the cooking methods which became lighter such as poaching and steaming
D. Larsen et al. / LWT - Food Science and Technology 44 (2011) 1814e1820
1819
Table 2 Correlations between the texture, flavour, aroma and colour intensity and DOL of cooked New Zealand King Salmon from the sensory evaluation. DOL Property
Intensity
PO
OB
PF
Texture
PO OB PF MW DF ST
0.433** 0.109 0.147 0.169 0.014 0.252
0.115 0.043 0.032 0.245 0.031 0.255
0.247 0.209 0.266 0.077 0.045 0.096
Flavour
PO OB PF MW DF ST
0.628** 0.164 0.099 0.404* 0.079 0.527**
0.178 0.165 0.113 0.161 0.035 0.06
0.138 0.152 0.275 0.378* 0.331* 0.383*
Aroma
PO OB PF MW DF ST
0.126 0.082 0.214 0.067 0.073 0.267
0.13 0.338* 0.085 0.037 0.036 0.089
Colour
PO OB PF MW DF ST
0.660** 0.27 0.218 0.253 0.287 0.248
0.199 0.679** 0.004 0.048 0.18 0.08
MW
DF
ST
0.165 0.087 0.118 0.071 0.318* 0.131
0.331* 0.254 0.122 0.054 0.079 0.109
0.321* 0.166 0.174 0.370* 0.238 0.392*
0.007 0.107 0.165 0.119 0.329* 0.207
0.653** 0.254 0.051 0.328* 0.008 0.403*
0.072 0.051 0.370* 0.016 0.237 0.118
0.057 0 0.031 0.105 0.108 0.222
0.114 0.295 0.319* 0.118 0.086 0.029
0.294 0.057 0.02 0.054 0.176 0.408**
0.16 0.257 0.21 0.116 0.605** 0.165
0.115 0.177 0.231 0.555** 0.188 0.298
0.247 0.258 0.424** 0.152 0.173 0.126
0.136 0.095 0.165 0.235 0.269 0.499**
0.072 0.359* 0.034 0.407** 0.064 0.064
Key: PO ¼ poached, OB ¼ oven baked, PF ¼ pan fried, MW ¼ microwaved, DF ¼ deep fried, ST ¼ steamed, and DOL ¼ degree of liking. ** Correlation is significant p < 0.01 (two-tailed). * Correlation is significant p < 0.05 (two-tailed). Fifty replicates per measurement.
(Table 1) were rated significantly less intense according to the sensory evaluation and these methods in turn were the least liked (although this was only significantly different compared with microwaved, pan fried and poached). This suggests that once King Table 3 Correlations between the texture, flavour, aroma and colour DOL and overall DOL of cooked New Zealand King Salmon from the sensory evaluation. Overall DOL Property DOL PO
OB
PF
MW
DF
ST
Texture
0.106 0.312* 0.145 0.395* PO 0.815** 0.017 OB 0.139 0.803** 0.002 0.025 0.052 0.227 0.09 0.075 PF 0.117 0.055 0.473** 0.381* MW 0.307 0.046 0.057 0.569** 0.012 0.099 ** 0.024 DF 0.094 0.037 0.275 0.128 0.691 * 0.039 0.104 0.192 0.266 0.701** ST 0.354
Flavour
PO 0.755** OB 0.046 PF 0.105 MW 0.173 DF 0.086 ST 0.367*
Aroma
PO 0.524** 0.178 0.114 OB 0.185 0.478** 0.203 PF 0.013 0.148 0.386* MW 0.042 0.266 0.062 DF 0.114 0.043 0.149 ST 0.117 0.305 0.016
Colour
0.07 0.830** 0.138 0.021 0.101 0.141
PO 0.299 0.162 OB 0.104 0.136 PF 0.264 0.026 MW 0.446** 0.212 DF 0.072 0.243 ST 0.143 0.005
0.005 0.227 0 0.344* 0.287 0.185 0.225 0.265 0.206 0.272 0.518** 0.155 0.193 0.15 0.553** 0.16 ** 0.182 0.004 0.176 0.769 0.136 0.328* 0.329* 0.653** 0.07 0.18 0.015 0.178 0.139 0.03
0.062 0.198 0.093 0.111 ** 0.242 0.583 0.400* 0.384* 0.204 0.249 0.025 0.295
0.182 0.529** 0.410** 0.172 0.052 0.113 0.016 0.035 0.199 0.463** 0.015 0.173 0.095 0.099 0.342* 0.209 0.388* 0.113
0.068 0.057 0.374* 0.540** 0.285 0.087
Key: PO ¼ poached, OB ¼ oven baked, PF ¼ pan fried, MW ¼ microwaved, DF ¼ deep fried, STt ¼ steamed, and DOL ¼ degree of liking. ** Correlation is significant p < 0.01 (two-tailed). * Correlation is significant p < 0.05 (two-tailed). Fifty replicates per measurement.
Salmon looses its ‘redness’ as it did during poaching and steaming, it becomes less desirable to the consumer. Whereas deep fried King Salmon had a significantly greater red colour (highest a* value) (Table 1) and was also rated as most intense. It had a significantly positive correlation between the colour DOL and overall DOL. The colour DOL of pan fried and microwaved was also correlated to their overall DOL (Table 3). This correlation indicated that liking or disliking the colour may have influenced how much the panellists liked or disliked the King Salmon sample overall. However, as with all these findings, it is important to state that correlation does not necessarily imply causation. Aroma was ranked the least important attribute of fish in the initial questionnaire. Generally, aroma is one of the most important properties of fish as it is a good indicator of freshness. The results showed that the methods that produced more intense aromas were more liked, such as deep fried and pan fried King Salmon; and the poached King Salmon had the least intense aroma and was liked the least. However, the oven baked King Salmon was most liked, although was rated to have a mid range intensity. The aroma DOL of poached, oven baked, pan fried and deep fried King Salmon and their corresponding overall DOL’s were correlated (Table 3).
Table 4 Instrumental texture measurements of raw and cooked New Zealand King Salmon. Cooking method
Hardness (N)
Cohesiveness
Springiness (mm)
Chewiness (N mm)
Raw Poached Steamed Microwaved Oven baked Pan fried Deep fried
0.70 0.1a 0.99 0.2a 0.93 0.2a 1.45 0.15a 1.21 0.3a 1.93 0.3a 2.52 0.2a
0.60 0.06a 0.65 0.08a 0.60 0.04a 0.62 0.05a 0.57 0.05a 0.67 0.08a 0.60 0.03a
0.22 0.01a 0.21 0.03a 0.22 0.02a 0.25 0.01a 0.27 0.01a 0.36 0.01a,b 0.52 0.01c
0.24 0.06a 0.27 0.02a 0.27 0.01a 0.43 0a 0.43 0.03a 0.84 0.1a,b 1.28 0.1c
Different letters in the same column indicate significant differences (p < 0.05). Twenty-seven replicates per measurement.
1820
D. Larsen et al. / LWT - Food Science and Technology 44 (2011) 1814e1820
Table 5 Mean sensory evaluation ratings on a 10 cm line scale of individual sensory attributes and DOL. Cooking method
PO ST MW OB PF DF
Colour
Aroma
Flavour
Texture
Overall DOL
Intensity
DOL
Intensity
DOL
Intensity
DOL
Intensity
DOL
2.79a 3.06a 4.27b 6.10c 7.58d 8.07d
3.53a,b 4.17b,e 5.33a,c,e 6.92b,c 6.13c,d 6.26d
3.26a 4.27a,c 4.63a,c 5.41b 6.50b,d 7.24d
3.99a,b 4.85b 4.33a,b 6.30c,b 6.02c,b,d 6.30c,b,d
4.19a 5.16b 5.49c 5.95a 5.39d 5.94a
4.65a 5.49a 4.79a 6.14a 5.70a 5.21a
2.93a 3.41a,c 3.28a,c 4.69b 5.85b 7.53d
4.56a 5.38a 5.16a 5.91a 5.83a 4.96a
4.29a,c 5.52b,c 4.94b,c 6.36b 6.18b 4.83b,c
Key: PO ¼ poached, OB ¼ oven baked, PF ¼ pan fried, MW ¼ microwaved, DF ¼ deep fried, ST ¼ steamed, and DOL ¼ degree of liking. Different letters in the same column indicate significant differences (p < 0.05). Fifty replicates per measurement.
Interestingly, the sensory data was correlated with a study investigating the effect that the same cooking methods had on the fatty acid profile of King Salmon that was run in tandem with the current study (Larsen et al., 2009). It was found that oven baked salmon actually had the highest levels of DHA, EPA and DPA amongst the cooked samples and was liked the most by consumers. This was also found with poached King Salmon which was least liked by the sensory panel and also had the lowest amount of DHA, EPA and DPA. This shows that potentially consumers are inadvertently choosing cooking methods that are actually the best at preserving the omega-3 levels. 4. Conclusions After cooking, the King Salmon became lighter, more red and more yellow as seen by instrumental colour analysis. Instrumental texture measurements showed an increase in the texture hardness and chewiness of King Salmon with cooking. The instrumental texture measurements were closely linked with sensory texture hardness and both texture DOL and flavour DOL showed significant positive correlations with their overall DOL for each cooking method. Overall oven baked and pan fried King Salmon were the methods with the highest DOL and were liked significantly more than the least liked cooking method, poaching. Acknowledgements We thank The New Zealand King Salmon Company and The National Foundation for Research Science and Technology, for providing funding for this study. References AOAC. (1999). Official methods of analysis of AOAC International. In W. Horwitz (Ed.) (16th ed.). Arlington, VA, USA: AOAC International. Bhattacharya, S., Choudhury, G. S., & Studebaker, S. (1993). Hydrothermal processing of Pacific Chum Salmon: effects on texture and in-vitro digestibility. Journal of Food Quality, 16, 243e251.
Birch, E. E., Hoffman, D. R., Uauy, R., Birch, D. G., & Prestidge, C. (1998). Visual acuity and the essentiality of docosahexaenoic acid and arachidonic acid in the diet of term infants. Pediatric Research, 44, 201e209. Cheng, C. S., Hamann, D. D., & Webb, N. B. (1979). Effect of thermal processing on minced fish gel structure. Journal of Food Science, 44, 1080e1986. Colangelo, L. A., He, K., Whooley, M. A., Daviglus, M. L., & Liu, K. (2009). Higher dietary intake of long-chain u-3 p.lyunsaturated fatty acids is inversely associated with depressive symptoms in women. Nutrition, 25(10), 1011e1019. Darlington, L. G., & Stone, T. W. (2001). Antioxidants and fatty acids in the amelioration of rheumatoid arthritis and related disorders. British Journal of Nutrition, 85, 251e269. Dunajski, E. (1979). Texture in fish muscle. Journal of Textural Studies, 10, 301e318. Erkkila, A. T., Lichtenstein, A. H., Mozaffarian, D., & Herrington, D. M. (2004). Fish intake is associated with a reduced progression of coronary artery atherosclerosis in postmenopausal women with coronary artery disease. American Journal of Clinical Nutrition, 80, 626e632. Foss, P., Storebakken, T., Schiedt, K., Liaaen-Jensen, S., Austreng, E., & Strieff, K. (1984). Carotenoids in diets of Salmonids. Aquaculture, 41, 213e226. He, K., Song, Y., Daviglus, M. L., Liu, K., Van Horn, L., Dyer, A. R., et al. (2004). Accumulated evidence on fish consumption and coronary heart disease mortality: a meta-analysis of cohort studies. Circulation, 109, 2705e2711. He, K., Liu, K., Daviglus, M. L., Jenny, N. S., Mayer-Davis, E., Jiang, R., et al. (2009). Associations of dietary long-chain n-3 p.lyunsaturated fatty acids and fish with biomarkers of inflammation and endothelial activation (from the Multi-Ethnic Study of Atherosclerosis [MESA]). The American Journal of Cardiology, 103, 1238e1243. Harrington, W. F., & von Hippel, P. H. (1961). The structure of collagen and gelatin. Advanced Protein Chemistry, 16, 1e138. Hutchings, J. B. (1999). Food colour and appearance (2nd ed.). Maryland, U.S.A.: Aspen publishers, Incorporated. pp. 347e348, 351, 512e513, 535. Krutulyte, R., Grunert, K. G., Scholderer, J., Skov Hagemann, K., Elgaard, P., Nielsen, B., et al. (2008). Motivational factors for consuming omega-3 PUFAs: an exploratory study with Danish consumers. Appetite, 51, 137e147. Larsen, D. S., Quek, S. Y., & Eyres, L. (2009). Effect of cooking method on the fatty acid profile of New Zealand King Salmon (Oncorhynchus tshawytscha). Journal of Food Chemistry., 119(2), 785e790. Pokorny, J. (1981). Browning from lipid-protein interactions. Progress in Food and Nutrition Science, 5, 421e428. Sigurgisladottir, S., Hafsteinsson, H., Jonsson, A., Lie, O., Nortvedt, R., Thomassen, M., et al. (1999). Textural properties of raw Salmon fillets as related to sampling method. Journal of Food Science, 64(1), 99e104. Skrede, G., & Storebakken, T. (1986). Characteristics of colour, in raw, baked and smoked wild and pen-reared Atlantic Salmon. Journal of Food Science, 51, 804e808. Szczesniak, A. S. (1963). Classification of textural characteristics. Journal of Food Science, 28, 385e389. Trondsen, T., Scholderer, J., Lund, E., & Eggen, A. E. (2003). Perceived barriers to consumption of fish among Norwegian women. Appetite, 41, 301e314. Verbeke, W., & Vackier, I. (2005). Individual determinants of fish consumption: application of the theory of planned behaviour. Appetite, 44, 67e82.