Impact of pre-slaughter stress on residual blood in fillet portions of farmed Atlantic cod (Gadus morhua) — Measured chemically and by Visible and Near-infrared spectroscopy

The objective of this work was to investigate if cod (Gadus morhua) which was exposed to crowding (149 kg/m3) and water currents prior to slaughter, would have a higher amount of residual blood in its fillets. This because residual blood can be detrimental for the perceived quality, farmed cod were divided into four groups; unstressed unbled (uu), unstressed bled (ub) stressed unbled (su) and stressed bled (sb). After 4 days ice-storage, all fish were filleted. Both left and right fillets were divided in 5 muscle portions. Dark muscle was removed from right fillet portions prior to VIS/NIR measurement. Chemical heme-pigment measurements were taken both from right- (white muscle) and left fillet portions (whole muscle), with an accuracy of 95.4 ± 3.2%. As expected, there were higher heme-pigment contents in unbled cod. In white muscle portions of bled cod (sb), the content was influenced significantly when fish were exposed to physical environment change prior to slaughter.In this work we also investigated if VIS/NIR spectroscopy could be used for assessing residual blood in intact cod muscle. Here we used chemical heme-pigment measurement as a reference. This research shows a correlation between Visible and Near-infrared (VIS/NIR) spectroscopy and chemical measurements. The VIS- (400–700 nm) or the NIR region (700–1100 nm) alone did not correlate as good as the complete VIS/NIR region (400–1100 nm, R2 = 0.83). This indicates that it may be possible to develop a spectroscopic method for measuring residual blood in intact cod muscle. However, further studies are warranted.