Effect of harvesting stress and slaughter conditions on selected flesh quality criteria of gilthead seabream (Sparus aurata)

The aim of this study was to assess the independent effects of harvesting stress and slaughter method on seabream flesh quality. Two groups of 32 gilthead seabream (mean body weight: 536 ± 96 g) were subjected to different pre-slaughter harvesting stress: profound anesthesia (PA, low stress condition) and net crowding (NC, high stress condition). Subsequently, fish from both harvesting stress conditions were slaughtered using either ice–salt water slurry (IW), to simulate commercial practices, or a lethal dose of anesthesia (LA), to isolate the effect of the pre-slaughter treatments. Rigor mortis was measured during the first 72 h after death, and muscle from the dorsal area was collected at regular intervals (0, 2, 6 and 48 h after death) during this period, for subsequent biochemical analysis of pH, TBARS, sulfated glycosaminoglycans and hydroxyproline content. Texture in raw and cooked fillets was measured instrumentally, using an Instron texture analyzer. The onset of rigor mortis was earliest for the NC–IW treatment, reaching highest values 2 h after death, while fish from the PA–IW treatment attained highest rigor scores 21 h after death. Resolution of rigor mortis started 3 and 32 h after death in fish subjected to NC and PA, respectively. Both harvesting stress and slaughter method had a significant effect (P < 0.05) on muscle pH, with highest values found in fish subjected to PA conditions, and in those slaughtered by lethal anesthesia. Muscle TBARS were significantly affected by harvesting stress. Collagen and sulfated glycosaminoglycan content of the samples decreased markedly through storage time, but were not significantly affected by harvesting stress conditions or slaughter method. In fish slaughtered in ice–salt water slurry, fillet hardness ranged between 5.0 ± 2.1 and 5.7 ± 1.8 N in raw fillets, and between 4.9 ± 0.9 and 5.6 ± 0.9 N in cooked fillets, but no significant differences among treatments were found. The use of zero withdrawal anesthetic improved muscle pH and delayed rigor mortis, although harvesting and slaughter stress had no major effect on muscle structure of gilthead seabream.