Muscle activity at slaughter: I. Changes in flesh colour and gaping in rainbow trout

High activity at slaughter is known to cause changes to the muscle biochemi stry in terms of muscle pH and adenosine triphosphate (ATP) content. This e xperiment looked at how the muscle activity may affect the flesh quality of fish. Electro-stimulation of a carcass immediately after death can be used as a model for high levels of muscle activity prior to death. This experim ent showed that electro-stimulation of 1.5 kg rainbow trout (Oncorhynchus m ykiss) immediately after slaughter not only resulted in short times to rigo r, but that the flesh colour was affected. The flesh became significantly l ighter (P < 0.001), less red (P < 0.001) and had higher chroma(P < 0.001) a s measured by the CIE [CIE, 1976. 18th Session, London, U.K., Sept. 1975. C IE Publication 36, Paris, France.] L*a*b* system, and the Roche colour card score was lowered (P < 0.01) compared to flesh from fish that had shown ve ry low levels of activity before slaughter and were nor electro-stimulated after death. The fillets were also more susceptible to gaping following the post-mortem stimulation (P < 0.001). This indicated that electro-stimulati on after death reduces the quality of the flesh. (C) 2000 Elsevier Science B.V. All rights reserved.