. Switzerland by four assessors. The fillets were then drawn, skin down, over a right
angle using a constant force. This simulated rough handling and potentially caused the appearance of gaping along the fillet, which was then scored subjectively by four judges,
Ž .
Ž .
Ž using a four point scale: 0 no gaping , 1 one or two breaks , 2 four or more small
. Ž
. breaks , or 3 large breaks .
The remaining 10 fish from each group were used to follow the progression of rigor. Ž
. A modified version of the apparatus used by Azam et al. 1990 was set up. The fish
were placed on a flat table so that the body behind the posterior end of the dorsal fin was hanging over the edge, unsupported. The angle between the horizontal and the line
from the corner of the table to the tip of the tail was then measured to the nearest 5 8
Ž .
termed the angle of droop . The fish were then turned over and the measurement repeated for the other side of the fish. The fish were measured at 0, 4, 8, 12, 20, 24, 34,
48, 56, 72 and 96 h after slaughter. In between measurements the fish were placed on ice in polystyrene boxes which were stored in a chiller at 4
8C. The significance of the differences between the groups in temperature, pH, lightness,
angle of hue, chroma and rigor development were tested at each time post-slaughter Ž
. using a repeated measures analysis of variance ANOVA . In order to determine the
rigor changes, the mean angle of droop for each fish was calculated from the two angles measured and then the ANOVA performed. This compensated for the fish setting at an
angle during rigor. The mean Roche colour card scores for each fish were compared using Student’s t-test. A Mann–Whitney U-test was applied to the non-parametric data
from the gaping scores.
3. Results
During anaesthesia the fish showed very little movement. Some slow swimming around the tank was observed, but many fish just held their position until unable to
move. At no point were any rapid movements observed. During the electro-stimulation, however, rapid contractions of the muscles resulted in a large degree of movement of the
whole fish. By the end of the 2-min stimulation the gross movements had almost stopped, but the muscles were still contracting as the fish obviously relaxed after the
cessation of stimulation.
Ž .
There was no difference in temperature between the groups at any point P 0.05 . However, the pH differed significantly between the groups until 56 h after slaughter
Ž .
P - 0.01 . Fig. 1 shows the changes in pH with time after slaughter. The anaesthetised fish showed a much slower rate of fall in pH, starting at 7.8 0.31 and dropping below
pH 7.0 after 22 h. By 45 h after slaughter the pH was below 6.6. In contrast, the electro-stimulated fish showed a very rapid drop in pH. Immediately after slaughter the
pH was 6.7 0.03 and after 2.5 h it had dropped below 6.6. The final pH of the flesh of the anaesthetised group was significantly higher than that of the electro-stimulated group
Ž
. P - 0.001 although the difference between the means was only 0.07.
There were differences in flesh colour between the anaesthetised and the electro- Ž
. Ž
. Ž
stimulated fish as measured by lightness Fig. 2 , angle of hue Fig. 3 and chroma Fig. .
4 . The anaesthetised fish, as determined by the repeated measures ANOVA, had
Ž .
Fig. 1. Changes in muscle pH of rainbow trout fillets with time after slaughter mean valuesS.E., ns10 .
Ž
U
. Ž
. significantly darker lower L
and redder lower angle of hue flesh, which had lower Ž
. chroma than the electro-stimulated fish P - 0.01 . This was confirmed by the differ-
Ž .
ence in the Roche colour card scores at the end of the storage period Table 1 . The
Ž .
Fig. 2. Changes in lightness of rainbow trout fillets with time after slaughter mean valuesS.E., ns10 . Increasing L
U
indicates increasing lightness.
Ž .
Fig. 3. Changes in colour of rainbow trout fillets after storage mean valuesS.E., ns10 . Increasing angle of hue indicates a more yellow colour and decreasing indicates a redder colour in the range 0–90
8.
scores for the anaesthetised fish were significantly higher than the electro-stimulated fish Ž
. P - 0.001 .
Ž .
Fig. 4. Changes in opacity of rainbow trout flesh after slaughter mean valuesS.E., ns10 .
Table 1 Mean Roche colour card and gaping scores for flesh of rainbow trout at the end of the 75-h storage period
Ž .
S.E.M. A higher gaping score indicates greater gaping of the flesh. A higher colour card score indicates a darker red
fillet colour. Anaesthetised
Electro-stimulated Significance of difference
between means Roche colour card score
15.00.18 14.20.23
P - 0.01 Gaping score
1.10.21 2.30.25
P - 0.01
The degree of gaping of the flesh was significantly affected by the treatment Ž
. P - 0.001 , with the anaesthetised fish showing less gaping after simulated rough
Ž .
Ž .
handling Table 1 . The time to the onset of rigor was delayed in these fish Fig. 5 . At each time there was a significant difference between the two groups, with the anaes-
Ž .
thetised fish showing resolution of rigor later than the electro-stimulated fish P - 0.001 . They also showed a greater angle of droop when in full rigor than the electro-stimulated
Ž .
group P - 0.001 , which indicated that these fish were more flexible than the electro- stimulated ones.
4. Discussion
