Jørgen Lerfall defended his thesis on September 23rd 2011

Ane Gro Siri Skjelfjord

The effect of pancreas disease and salting conditions on the quality of raw and cold-smoked Atlantic salmon (Salmo salar L.)

Summary from the thesis - PhD thesis 2011:07

Fillet quality of farmed Atlantic salmon (Salmo salar L.) is affected by a broad range of pre- and post-mortem factors. This thesis focuses mainly on the impact of pancreas disease (PD), salt composition and salting method on pigment concentration and colour of raw and cold-smoked salmon fillets, but fillet composition, texture and drip losses are as well considered.

The fish material used to study effects of PD on fillet quality was sampled from commercial farming locations to obtain a broad overview and identify potential common properties of PD affected salmon (Paper I). The farming locations participated in a cohort study reported by Jansen et al. (2010), hence the salmon were sampled from populations with a well documented disease history. Salmon from seven farms were diagnosed with PD (diagnosed 0-12 months prior to slaughtering); salmon from one farm were infected with salmonid alpha virus (SAV) without an outbreak of PD, whereas salmon from two farms had no records of PD diagnosis and worked as control farms. To obtain knowledge on underlying causes to quality deviations of PD affected salmon, individuals with different PD pathology within a population diagnosed with PD at time of slaughtering was investigated (Paper II). Anecdotal information indicates that PD may cause poor general muscle quality and in particular pale and irregular colouration. Salmon diagnosed with PD at slaughter, or six months prior to slaughter confirmed this. Changes in quality in the order of their appearance were decreased CF, depleted muscle glycogen, increased drip loss of raw muscle, paler colour, depleted protein and finally harder texture in smoked salmon fillets. Salmon infected with salmonid alphavirus (SAV) without a PD outbreak and salmon diagnosed one year before slaughtering, had similar quality as unaffected fish, although paler colour might occur even after one year recovery. Within a population of farmed Atlantic salmon diagnosed with PD at time of slaughtering, a large variation was observed among individuals in pathological profile, gene expression profile in heart tissue, and fillet quality characteristics. Deteriorated quality and dysfunction of the digestive system was most pronounced in fish with severe loss of pancreas.

Dry salting significantly reduced the stability of carotenoids in the fillet surface of cold-smoked salmon fillets as compared to injection salting (Paper IV). The salt content in pre rigor injection salted fillets was similar as those salted post rigor (2.4% versus 2.6%, respectively), whereas the fillet colour was more translucence. However, injection salting of pre rigor fillets can be recommended. Moreover, state of rigor mortis at time of salting had no effect on the carotenoid stability. Low correlations between colorimetric parameters and content of carotenoids in the fillet surface, illustrated that additional factors affects the visual appearance of cold smoked salmon.

Nitrite salt curing (Paper III) improved the colour of cold-smoked salmon fillets (more reddish, darker and less yellowish). However, only slight higher carotenoid stability during processing was observed. The improved colour was most probably related to formation of nitrosomyoglobin. Salmon fillets treated with nitrite (fine refined salt added 0.6% sodium nitrite) had a relatively high amount of residual nitrite, however higher contents of N-nitrosoamines were not observed.

It is concludcd that salmon diagnosed with PD at slaughter, or six months prior to slaughter showed deteriorated fillet quality, whereas salmon infected with salmonid alphavirus (SAV) without a PD outbreak and salmon diagnosed one year before slaughtering, had similar quality as unaffected fish. Moreover it is concluded that nitrite salt improved the appearance of cold-smoked salmon fillets and dry salting reduced the stability of carotenoids in the fillet surface as compared to injection salting.

Updated: 23.09.11
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