Effects of Perimortem Stress on Farmed Atlantic Cod Product Quality: A Baseline Study

Abstract

The potential effects of handling stress on the product quality of farmed Atlantic cod were studied in a controlled experiment (fish anesthetized with metomidate or isoeugenol, or subjected to stress by chasing for 30 min). For comparison, stress and fillet quality was also studied for commercially slaughtered farmed cod (fish sampled from waiting cage, after pumping and stunning with carbon dioxide, and after bleeding and chilling). Baseline values for stress-related parameters (blood chemistry, muscle high-energy phosphates and inosine monophospate, initial pH, muscle twitches, and rigor mortis) of rested Atlantic cod have been established. Since our stress bout showed that this species was not easily excitable, we were less convinced that we actually did study the other extreme, namely, exhausted fish. Nevertheless, the present data from the commercial slaughter of cod suggested that our stress bout was of adequate magnitude to represent potential poor handling routines. Our results consistently showed largely no differences between treatments, and that perimortem handling stress did not cause inferior flesh quality. This suggested that farmed cod can be processed with little risk of reducing product quality (quality index, fillet water content, water-holding capacity, ultimate pH, adenosine triphosphate-related degradation products and K-value, skin and fillet color, water and salt-soluble proteins, hardness, and gaping). For better maintenance of skin appearance after storage, the importance of storing the gutted cod on the belly, avoiding direct contact between skin and crushed ice, is demonstrated.

Quality of Atlantic Cod Frozen in Cell Alive System, Air-Blast, and Cold Storage Freezers

“…Our values are practically identical to the values reported by Mørkøre and Lilleholt (2007) after thawing of farmed cod frozen at -10, -25, -40, -55, and -70°C. Similar values were also determined in rested farmed cod after ice storage for 7 days (Erikson et al, 2011).…”

“…Typical ultimate pH values in farmed cod range from 6.3 (Erikson et al, 2011) to 6.5 (Erikson et al, 2012). As measured just after thawing, our present values were around pH 6.4, independent of freezing method (p > 0.05).…”

“…1-17.6, 16.1-19.5, and 2.3-3.3 µmol (g d ry wt) -1 , respectively. The corresponding K-values were about 50% (Erikson et al, 2011). In another study, the K-values after 7 days on ice were 53-68% (Digre et al, 2011b).…”

“…The values were reduced from about 79-81 % just after thawing to about 70-72% after subsequent ice storage (Table 5). Unfrozen farmed cod show a considerably higher ability to retain water after 7 days on ice, with WHC values of 80-83% (Digre et al,201 la) and 86-87% (Erikson et al, 2011). Freezing and thawing of wild-caught Atlantic cod reduced WHC from about 85% (fresh fish) to 82% (Erikson et al, 2004).…”

“…Recovery to rested state did indeed take place (Table 2). Typical blood and muscle values of rested or anesthetized farmed cod are: lactate 0.3 to 0.4 mmol L-1 (Brown et al, 2010), initial white muscle pH about pH 7.6, and twitch ability 3.0 (Erikson et al, 2011). Thus, in terms of handling stress it is clear that the CSF and CAS2 fish were dose to being in the rested state, whereas the CAS 1 fish were stressed at the time of killing and freezing.…”