luxury food for centuries, and it is often asserted that the eating quality of wild salmon is better than that of farmed fish.
The possible quality differences between wild and farmed salmon have been the subject of research for both the Atlantic salmon and the various species of Pacific
Ž .
salmon Oncorhynchus sp. ; some authors have reported differences in eating quality between wild and farmed salmon while others have found no difference. Sylvia et al.
Ž .
1995 found that the wild salmon had more ‘delicate, fresh fish flavour’ but no difference in texture from farmed salmon. In terms of colour, the flesh of wild salmon
Ž .
has also variously been reported to have less yellow hue Skrede and Storebakken, 1986 Ž
. and more red colour Higgs et al., 1989 than that of their farmed equivalents. Sensory
differences in colour, texture or flavour have also been reported between wild and Ž
cultured fish of other species Hatae et al., 1989; Aoki et al., 1991; Prescott and Bell, .
1992; Orban et al., 1997 . In contrast, other authors have reported that the eating quality Ž
of farmed salmon is similar or preferred to that of wild Bartos, 1989; Higgs et al., .
Ž 1989 . Thus, the effect of domestication on the eating quality of Atlantic salmon and
. other fish species remains unclear. The above studies have compared fish from only
two or three sources for any one species of salmon and it is possible that any sensory differences observed could be entirely due to the difference in location. Considerable
sensory differences can exist between trout from two farms from the same region Ž
. Farmer, unpubl. data . Thus, the primary purpose of this investigation was to examine
sensory differences between farmed and wild Atlantic salmon from a total of eight locations in Northern Ireland, the Republic of Ireland and Scotland. As it was necessary
to conduct these studies on frozen fish, a short investigation was also conducted to check the effect of frozen storage on the sensory attributes under examination.
2. Materials and methods
2.1. Comparison of fish from different sources Farmed and wild salmon were obtained from a total of eight sources in Northern
Ireland, the Republic of Ireland and Scotland during 1993 and 1994, as shown in Table 1. The method of capture and slaughter was inherently different between sources.
Salmon from River 1 were caught in salmon traps and slaughtered by exposure to elevated concentrations of CO
and a blow to the head. Salmon from River 3 were
2
caught by hook and line. Salmon from the remaining wild sources were caught using Ž
. Ž
. drift nets sea or draught nets river and either died in the nets or were killed by a blow
to the head. Salmon from Farm 3 were also killed by a blow to the head while those from Farms 1 and 2 were asphyxiated using CO . Those from Farm 1 were also bled by
2
Ž gill removal. All salmon were harvested during the period June to August the wild
. salmon season and were held on ice until transported to the laboratory within 3 days of
harvest. Salmon were supplied as whole, uneviscerated fish of weights within the range 2 to 3
kg, when possible. However, the weights of the fish depended on availability, especially for the wild fish, and ranged from 1.3 to 3.6 kg. Ages to smoltification and capture or
Table 1 Sources of salmon
a
Name Source type
Location 1993
1994 Ž
. Farm 1
Sea-farmed SF Pens in enclosed sea lough.
U U
Ž .
Farm 2 Sea-farmed SF
Pens in off-shore location U
U Ž
. Farm 3
Sea-farmed SF Onshore tanks with pumped sea-water
U U
Ž .
Sea 1 Sea-wild SW
Saltwater location near mouth of River 1 –
U Ž
. Sea 2
Sea-wild SW Saltwater location near mouth of Rivers 2r3
U U
Ž .
River 1 River-wild RW
3 km from river mouth U
U
b
Ž .
River 2 River-wild RW
24 km from river mouth U
b
Ž .
River 3 River-wild RW
4 km from river mouth U
a
‘Lough’ is the local name for either a partially enclosed sea water inlet or a freshwater lake.
b
Combined and treated as one source during 1993 due to low numbers captured.
harvest were determined by reading annuli in the fish scales, under a binocular microscope. Both wild and farmed salmon were 2 or 3 years old and had spent one
winter at sea. The fish were stored in a chill-room at 0–28C until evisceration, which occurred
within 5 days of harvesting and after the resolution of rigor mortis. The pelvic and dorsal fins were removed and the region between the pectoral fin and the cloaca was cut
Ž .
perpendicular to the long dimension of the fish into steaks approx. 25 mm thick ; these were labelled A to I or J in the direction of head to tail. Generally, steaks B, D, F, H and
J were used for sensory evaluation. The steaks were immediately vacuum-packed in Ž
laminated vacuum pouches nylon 20 mm, polyethylene 60 mm; Brow Packaging, .
Belfast , frozen and stored at y24 38C until required. As salmon from all sources were harvested throughout the wild salmon season and were analysed over a period of
3–4 months, the duration of frozen storage prior to sensory analysis ranged from 5 to 18 weeks in the 1993 trial and from 8 to 24 weeks in the 1994 trial.
2.2. Effect of freezing Ž
. Salmon from Farm 2 and Farm 3 average weights 2.8 kg and 2.7 kg were harvested
during February and April 1994, respectively. Salmon steaks were prepared and Ž
. vacuum-packed as described above. Salmon steaks to be analysed when fresh unfrozen
were refrigerated for 1–2 days prior to sensory analysis; the remainder were immedi- ately frozen and stored at y24 38C for 3–14 days prior to analysis.
2.3. Effect of length of frozen storage Salmon from Farm 2, weighing on average 2.7 kg, were harvested between August
Ž .
1993 and February 1994. The salmon were again frozen as steaks as described above and stored at y24 38C for 33, 15, 8 and 4 weeks before the commencement of
sensory analysis.
2.4. Sensory analysis Ž
. Salmon steaks were thawed at 48C, overnight , washed and cooked using a bain
marie method; the steaks were wrapped in grease-proof paper, fold uppermost and
Ž .
placed individually on inverted, perforated aluminium trays 180 = 120 mm which were placed in stainless steel baking trays. Tap water was added to a depth of 10 mm and the
whole tray covered in aluminium foil. The steaks were cooked for 20 min in a Ž
. fan-assisted oven Falcon E1102, Glynwed Appliances, Larberth, Scotland . Different
Ž .
cooking temperatures were used for the 1993 salmon 1808C and the 1994 salmon Ž
. 2008C due to differences in the numbers of steaks in the oven. The ultimate internal
temperature ranged from 768C to 858C depending on the size of steaks. Each panellist received one half steak served on a heated porcelain plate; a small portion from the
Ž .
ventral region was served separately in a heated, lidded porcelain dish 80 mm diameter Ž
for odour assessment. Tap water, filtered through a domestic water filter Boots the .
Chemist, Nottingham, UK to remove any extraneous flavours, and water biscuits were supplied as palate cleansers. All panels were conducted in ventilated booths under N-sky
Ž lighting and the data collected using ‘PSA 1.64’ data collection software Oliemans,
. Punter Partners, Utrecht, the Netherlands .
Ž .
Quantitative descriptive analysis or sensory profiling Stone et al., 1974 was used to analyse salmon from various sources. A list of attributes describing aroma, appearance,
flavour, texture and aftertaste was generated and refined, after discussion, by a trained panel to eliminate repetition and redundant descriptors, and to agree on the definition of
Ž .
each attribute Table 2 . Prior to the 1994 season the attributes were further refined, after additional training and discussion, in the light of experience gained during 1993. Ten
panellists assessed salmon harvested in 1993 using 32 attributes, while eight people used 37 attributes for the 1994 trial. One salmon from each source was assessed by all
panellists during a panel session; for salmon harvested during 1993, a total of 20 salmon from each source were assessed, while 10 salmon from each source were used during
1994. The experimental design used in the 1993 trial involved randomising the order of presentation for each panellist. For the 1994 trial, an 8 = 8 Latin square, balanced for
Ž .
presentation order and first-order carry-over effects, was used MacFie et al., 1989 . Ž
. Random permutations Cochran and Cox, 1957 were used to apply blocks of the design
to panel sessions. Sensory profiling was also conducted on fresh and frozen salmon, and on salmon
frozen for different lengths of time, using 32 attributes, as described above for the salmon harvested during 1993.
Hedonic scaling was conducted using 40 untrained panellists, drawn from staff members unfamiliar with the study, who subjectively assessed the acceptability of the
aroma, appearance, flavour, texture and aftertaste as well as the overall acceptability of salmon obtained from 6 sources during 1993. Salmon samples were scored using an
Ž . eight point hedonic scale ranging from extremely acceptable 1 to extremely unaccept-
Ž . able 8 .
2.5. Statistical analysis Ž
The salmon profiling data comprised measurements on 120 fish 20 panel sessions, 6 .
Ž .
sources in 1993 and 80 fish 10 sessions, 8 sources in 1994. Each fish was assessed by 10 panellists in 1993 and 8 panellists in 1994. In order to compare the sources, separate
Table 2 Definitions of descriptors used for profiling studies
a
Arrributes Definitions
Odour Salmon-like
Intensity of distinctive salmon-like odour Ž
. Oily
Intensity of oily fish oils odours Salty
Intensity of salty odour Earthy
Intensity of any earthyrpeaty odour Stagnant
Intensity of any stagnant water odour Ž
. Farmyard 1994
Intensity of manurercow-dung odour Appearance
Pink Intensity of pink colour in the uncut steak
Peach Intensity of peach colour in the uncut steak
Orange Intensity of orange colour in the uncut steak
Beige Intensity of beige colour close to the skin
Ž .
Whiteness 1993 Intensity of white colour in the uncut steak
Ž .
Paleness 1994 Intensity of paleness in the uncut steak
Coagulation Amount of coagulation that appears on the surface of the salmon steak
Juicy appearance Amount of juice that has seeped onto the plate from the salmon
Separation Oiliness of the juice seeping out of the salmon.
Moist appearance Visible moistness of steak when cut with knife
Flaky Visible flakiness of steak when cut with a knife
Ž .
Crumbly 1994 Crumbliness of steak when cut with a knife
FlaÕour Salmon-like flavour
Intensity of distinctive salmon-like flavour Ž
. Salty flavour 1994
Intensity of salt-like flavour Oily flavour
Intensity of fish oil flavour Fishy flavour
Intensity of any other fish-like flavours Ž
. Fishy flavour skin, 1994
Intensity of non-salmon fishy flavour near the skin of the salmon steak Earthy flavour
Intensity of earthy or peaty flavour Farmyard flavour
Intensity of manurercow-dung flavour Ž
. Smokiness 1993
Intensity of smoky flavour Texture
Ž .
Tenderness 1993 Tenderness of salmon on first few bites
Ž .
Firmness 1994 Firmness of salmon on first few bites
Ž .
Springiness 1993 Springiness of salmon on first few bites
Moist texture Amount of moisture released on chewing
Light texture Lightness and smoothness of salmon in mouth
Chewiness Amount of chewing required before swallowing
Flakiness Degree to which the salmon breaks down into flakes in the mouth
Clinginess Degree to which the salmon clings to the mouth and teeth
Aftertaste Time
Time when aftertaste starts Overall aftertaste
Intensity of aftertaste Earthy aftertaste
Intensity of earthy aftertaste Metallic aftertaste
Intensity of metallic aftertaste Chicken-like aftertaste
Intensity of chicken-like aftertaste Ž
. Oily aftertaste 1994
Intensity of fish oil aftertaste
a
Attributes were selected by the panels used for both the 1993 and 1994 seasons, except where the season of use is indicated.
Ž .
analyses of variance ANOVA were carried out in each year, based on individual fish means for the various attributes. The effects of sessions were removed in the analyses
providing a total of 105 and 63 residual degrees of freedom, respectively, for the 2 Ž
. years. When significant P - 0.05 differences were found between the sources, Dun-
can’s multiple range test at a probability level of P s 0.05 was used to establish Ž
. significant differences O’Mahoney, 1986 . Data for hedonic scaling were also analysed
Ž by ANOVA and Duncan’s Test. While data obtained by hedonic scaling or, for that
. matter, profiling
may not be strictly linear and therefore may not fulfil all the assumptions for these parametric tests, they are still useful methods for the interpretation
Ž .
of such data O’Mahoney, 1986 . This should be less of a problem for the profiling data as reference to the Central Limit Theorem implies that the assumption of a Normal
Distribution for means over panellists may be reasonable. However, this is not the case for the hedonic scaling data and, accordingly, these were also analysed by the nonpara-
metric Kruskal–Wallis rank sum test which does not assume normality of the observa-
Ž .
tions. This showed significant differences P - 0.05
for appearance, flavour and aftertaste in agreement with the parametric tests. Hence, this paper concentrates on the
results of the parametric tests. Correlation coefficients were calculated to determine whether there was any relation-
ship between the mean scores obtained by hedonic scaling for acceptability and the mean scores for each profiling attribute for the six salmon sources assessed in 1993.
Regression analysis using quadratic terms was also conducted to check for possible curvilinear relationships.
Ž .
Principal components analysis PCA was conducted on the mean profiling scores for each individual salmon assessed, for both years of study, using the Genstat 5 statistical
package and based on the sums of squares matrix between the attributes as the observations were on a common scale.
3. Results
