Cold shock by immersion in iced salty water is a suitable method to stun Carpione del Garda (Salmo carpio) both considering animal welfare and flesh quality during storage

The effect of the method of stunning/killing both on animal welfare and on quality of the final product is one of the most critical process that influences adenosine 5-monofosphate (ATP) depletion but also quality-related parameters such as pH, colour and water holding capacity (WHC). Despite the request of the European Commission to identify species-specific stunning systems, many works need to be done. Carpione del Garda (Salmo carpio) is a salmonid endemic of Lake Garda whose meat are highly appreciated. However, scarce are the studies aimed to investigate the effects of stunning methods on flesh quality. Seventy-two Salmo carpio (347.4±68.9g) specimens were randomly and equally sorted into three experimental groups (24 fish per treatment) based on the stunning method: (i) lethal dose of anaesthetic (AN, 400mg/L MS-222), used as control; (ii) electrical stunning (ES, 24 V applied for 4 s); (iii) cold shock by immersion in iced salty water (ICE, 30 s at -3 °C; NaCl 35 ppt). ATP and related catabolites in muscle immediately after death were analysed to obtain ATP to inosine monophosphate (IMP) ratio; colour parameters, pH, water holding capacity (WHC), fatty acid profile, conjugated dienes and thiobarbituric acid reactive substances (CD and TBARS, respectively) were determined immediately after death and after a storage of 30, 60, and 90 days at -20 °C. The results obtained from the statistical analysis (two-ways ANOVA) highlighted that the AN and ICE groups had higher ATP/IMP ratio (57.3 and 41.4, respectively), than ES (10.7). pH value of AN samples (6.5) was higher than the value found in ES fillets (6.32; p<0.05); a pH drop (p<0.001) was observed after 30 days of storage irrespective to the stunning method applied. WHC resulted unaffected by stunning and storage. The ICE fillets were brighter (L*: 54.9) than the ES ones (52.48), whereas redness (a*) and yellowness (b*) indexes were modified by the storage. Noteworthy, the AN group showed a high lipid oxidation level (p<0.01), since a higher (p<0.01) TBARS content was observed after 60 days of storage (>0.10mg MDA/100g fillet) compared the values found in the other groups, despite the fatty acid profile of the fillets at the beginning of the trial did not differ. In conclusion, with the attempt to find the best compromise between fish welfare and flesh quality, cold shock by immersion in iced salty water could be suggested for Salmo carpio stunning.