Slaughtering procedures on the flesh quality of frozen stored pacu

Pacu ( Piaractus mesopotamicus ) is one of the most important fish farmed species in Brazil due to its hardy, fast growing, omnivorous feeding behavior, and good consumers acceptance. However, studies on the effect of different slaughtering procedures on quality of frozen pacu fillets have not been carried out. Therefore, this study aimed to evaluate the effect of electrical stunning, CO 2 narcosis, or water/ice immersion on the quality (lipid oxidation - TBARS, protein oxidation - carbonyl and thiols, protein denaturation, and instrumental color – L*, a*, and b*) of frozen (-18 °C) pacu fillets stored for up to 6 months. Electrical stunning became the fillets darker and red, besides leading to higher protein oxidation (carbonyl and thiols), and protein denaturation. CO 2 narcosis resulting in more pale flesh, with higher protein oxidation. The slaughtering by water/ice immersion was the best alternative for obtaining high quality frozen pacu fillets with lower oxidation and protein denaturation. A quality loss was observed for all pacu fillets stored at -18 °C over the months, as evidenced by the increase in lipid and protein oxidation, color changes, and higher protein denaturation. Additionaly, a maximum storage period of 3 to 4 months is recommended for frozen pacu fillets