Comparing stunning methods and seasonal effects on biochemical variables and product quality of rainbow trout

This study compared live chilling (LC) and dry electrical stunning at higher (HI: 400 mA for 0.5 s followed by 200 mA for 1.5 s) and lower (LI: 200 mA for 2 s) intensities in combination with live chilling in rainbow trout (Oncorhynchus mykiss), evaluating their impact on muscle damage, metabolism, and sensory attributes under winter and summer. Trout were stunned, slaughtered and samples were taken for biochemical markers, muscle pH, rigor mortis, texture, color and freshness analysis. Our results showed that stunning method and seasonal conditions significantly influenced product quality, with low-intensity electrical stunning being most effective under warmer conditions. Blood levels of lactate dehydrogenase (LDH) and creatine phosphokinase (CPK) were highest in LC and HI groups, indicating greater muscle damage, compared to LI. Osmolality was also elevated in HI, suggesting increased cell damage. Seasonality influenced muscle metabolism: summer results, compared with winter, showed lower glycogen reserves and reduced glycolytic enzyme activity (lower HK, PK, LDH activity), along with increased gluconeogenesis (higher FBP activity), and also altered oxidative stress, evidenced by up-regulated sod and gst gene expression and down-regulated gpx and cat expression in muscle. Muscle pH at 0 h post-mortem was lowest in LC, while rigor mortis developed faster in this group in summer. Texture analysis showed an interaction between stunning method and season, with slightly higher cohesiveness in LI group in summer. Seasonal effects on texture included lower hardness and springiness but higher adhesiveness in summer. Despite differences, no significant variations in color stability or freshness between stunning methods were observed.