Rainbow trout (Oncorhynchus mykiss) farmed at two different temperatures: Post rigor mortis changes in function of the stunning method

Abstract

Post rigor mortis changes of texture, chemical and sensory properties in rainbow trout (Oncorhynchus mykiss) reared at two different temperature conditions (8 and 12 °C) were examined to better understand how different stunning methods, i.e. electroshock (E) and asphyxia with carbon monoxide (CO), can influence their evolution during refrigerated storage. Seven days after rigor resolution (T_RR7), considering ATP catabolites (K- and K1-values), the freshness remained well preserved regardless of the stunning method applied and water temperature. During refrigerated storage fillets from fish reared at 8 °C maintained significantly higher (P < 0.001) pH at the day of rigor resolution (T_RR0), whereas at the end of the storage time (T_RR7), 8 °C-reared fish showed a significantly lower pH value (P < 0.05). CO treatment was effective in ensuring a more intense red colour of the fillet and high chroma, whereas E treatment exhibited the lowest a*, b* and chroma values. The texture profile analysis showed a significant effect of the stunning method (S), water temperature (T) and S × T interaction on fillet cohesiveness. TBARS values were significantly lower (P < 0.05) in fish stunned by CO when compared to E group in the first 76 h post mortem (T_RR0). At the end of the storage period (T_RR7), no TBARS value difference was detected between treatments. The stunning method had a relevant impact on fillet sensory traits, revealing that CO fillets were the juiciest (P < 0.05) and presented the lowest saltiness (P < 0.05), aroma (P < 0.05) and odour (P < 0.01) intensity. Rearing temperature, instead, had a moderate effect on fillet sensory traits and indicated that the water temperature of 12 °C enhanced juiciness (P < 0.05) and tenderness (P < 0.05) attributes. Overall results suggested that CO is a suitable stunning method for trout that, coupled with 12 °C water temperature, are able to preserve fillet freshness, enhance colorimetric characteristics which are maintained during refrigerated storage, and provide desirable sensory traits.