Effect of carbon monoxide for Atlantic salmon (Salmo salar L.) slaughtering on stress response and fillet shelf life Anna Concollato a,c , Giuliana Parisi a, ⁎, Rolf Erik Olsen b , Bjørn Olav Kvamme b , Erik Slinde b , Antonella Dalle Zotte c a Department of Agri-Food Production and Environmental Sciences, Section of Animal Sciences, University of Firenze, Via delle Cascine 5, 50144 Firenze, Italy b Institute of Marine Research, P.O. Box 1870, N-5817 Bergen, Norway c Department of Animal Medicine, Production and Health, University of Padova, Viale dell’Università 16, 35020 Legnaro, Padova, Italy abstract article info Article history: Received 29 March 2014 Received in revised form 24 May 2014 Accepted 27 May 2014 Available online 6 June 2014 Keywords: Carbon monoxide Stunning Catecholamines Fish quality Shelf life The effect of carbon monoxide (CO) as stunning method in Atlantic salmon (Salmo salar L.) on stress indicators (adrenaline, A; noradrenaline, NAD) and on fillets quality during the shelf life has been investigated. The CO was dissolved into tanks with salmon for 8 and 20 min to obtain fish groups CO8 and CO20, respectively. These groups were compared to a non-stressed control group (C). All the fish were hauled out from the tank and killed by percussion. Adrenaline content of CO20 group was 1.8 and 1.7-fold higher than CO8 and C groups respectively (P b 0.001), which exhibited similar values. Noradrenaline content was higher in CO20 than in C group (8.1 vs. 5.4 ng/ml plasma; P b 0.0001). The CO treatment resulted in a small significant increase in light- ness and yellowness, not altering the overall “natural” colour of the fillet. CO treatment caused a rapid onset of rigor mortis and a small but significant increase in drip loss (P b 0.05). © 2014 Elsevier B.V. All rights reserved. 1. Introduction Fish quality can be influenced by pre, ante and post mortem con- ditions, including handling before slaughter, slaughtering methods and storage conditions. Animal welfare has become a crucial issue for farmed fish. There are no optimal stunning conditions available today. Carbon monoxide (CO) has proven not to provoke the aversive reactions (Smith, 2001) as seen with CO 2 (Poli et al., 2005). The effec- tiveness of CO is due to its displacement of oxygen on heme proteins (haemoglobin (Hb), myoglobin (Mb) and neuroglobin (Ngb)), causing tissue hypoxia (Brunori and Vallone, 2007; Davenport, 2002; Kalin, 1996). The effect is quick sedation and unconsciousness and the animal will die due to O 2 shortage without sensing the deficiency. It is also be- lieved that CO binds to the oxygen-storage proteins in Saccus vasculosus, a well-vascularised organ situated in the ventral side of the brain with several putative functions during hypoxia and stress, but also as oxygen depot and transport (Burmester and Hankeln, 2009; Sanson, 1998; Yanez et al., 1997). CO has been used for decades as food preservative in food indus- try (Sørheim et al., 2001). However, CO has also been demonstrated to mask spoilage as the cherry red colour can last beyond the micro- biological shelf life of the meat (Kropf, 1980). Consequently, the use has been discontinued for meat in many countries (Wilkinson et al., 2006). CO is also known to improve colour stability in red muscles (Chow et al., 1998; Kowalski, 2006), reduce microbial growth (Gee and Brown, 1981) and lipid oxidation (Cornforth and Hunt, 2008; Hsieh et al., 1998) even when live fish is exposed to CO (Mantilla et al., 2008). The latter is particularly interesting in fatty fish like salmon, which is vulnerable to lipid oxidation due to the high level of unsaturat- ed fatty acids. When CO is added, it binds directly to oxymyoglobin/ oxyhaemoglobin (OMb/OHb), displacing oxygen, producing COMb/ COHb that has a cherry red colour. They are stable compounds and the degradation to meth-forms MMb/MHb takes longer time (Chow et al., 1998) and will thus prevent discolouration. In Atlantic salmon, herring and mackerel anaesthetized by injecting CO in seawater, redness (a* value) was more persistent than the control groups; moreover CO treated fish did not develop the typical rancid smell even after 6 days of cold storage as was the case of the controls (Concollato et al., in press). The autoxidation of heme protein to meth-forms is also a critical step in lipid oxidation. MMb/MHb reacts with peroxides and stimulates formation of chemical compounds able of initiating and propagating lipid oxidation (Everse and Hsia, 1997; Mantilla et al., 2008; Shahidi and Botta, 1994), which is a major cause of quality deterioration in sea- food, contributing to the formation of off-odours, off-flavours and tex- ture declining. Since CO is expected to retard lipid oxidation of Hb and Aquaculture 433 (2014) 13–18 ⁎ Corresponding author. Tel.: +39 055 3288265; fax: +39 055 321216. E-mail address: giuliana.parisi@unifi.it (G. Parisi). http://dx.doi.org/10.1016/j.aquaculture.2014.05.040 0044-8486/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aqua-online