Texture, gaping and colour of fresh and frozen Atlantic salmon flesh as affected by pre-slaughter iso-eugenol or CO 2 anaesthesia

Abstract

Farmed Atlantic salmon ( Salmo salar L.) were slaughtered at an average weight of 5.5 kg in May 2001 under either traditional CO 2 anaesthesia (denoted high stress) or a two-step iso-eugenol anaesthesia (denoted low stress) before being bled to death in chilled seawater. Product quality analyses were performed on fillets after 5 days on ice and on cutlets after 12 months of frozen storage (−25 °C). In ice-stored fillets, no differences in gaping were observed between the two anaesthetic protocols, but instrumental analyses revealed that the flesh of the salmon exposed to CO 2 sedation was softer and slightly redder (higher a*-value, 27.1±0.1, S.E. versus 26.4±0.1, p<0.0004) and more yellowish (higher b*-value, 22.6±0.1 versus 22.0±0.1, p<0.0001) than the salmon anaesthetised using iso-eugenol. Analyses of frozen–thawed cutlets confirmed the fresh fillet results in that salmon anaesthetised using iso-eugenol were firmer and paler (RocheSalmoFan™ score, 23.5±0.4 versus 24.4±0.3, p<0.05) than the salmon anaesthetised using CO 2. Furthermore, the frozen and thawed cutlets of iso-eugenol-anaesthetised salmon had a higher muscle pH (6.15±0.01 versus 5.98±0.03, p<0.05) and lower liquid loss (5.1±0.3 versus 7.1±0.3, p<0.05). Individual growth rate, final body weight (BW), final body length, condition factor (CF), sex, gonadosomatic index (GI) were also registered. No significant correlations ( p>0.15) between these growth and body conformation variables and gaping or fillet softness were detected. In conclusion, no differences were observed in fillet gaping between the two anaesthetic protocols, but the salmon anaesthetised using iso-eugenol were firmer, paler and had a higher water-holding capacity than salmon exposed to CO 2 anaesthesia.