Slaughtering method and dietary α-tocopheryl acetate supplementation affect rigor mortis and fillet shelf-life of turbot Scophthalmus maximus L.

The effects of dietary α-tocopheryl acetate supplementation and different slaughtering methods were investigated on the flesh quality of farmed market-size turbot Scophthalmus maximus (L). Turbot were divided into three groups and fed commercial diets, supplemented with different levels of α-tocopheryl acetate at the following dietary inclusion levels: 72 (100), 547 (500), 969 (1000) (mg of α-tocopheryl acetate kg^-1 diet, analytical values with diet codes in brackets). After 5 months, fish (mean weight 1056 ± 19.7 g) from each dietary treatment were sampled, applying three different slaughtering methods: (A) bleeding in ice water; (B) thermal shock, no bleeding; (C) percussion followed by bleeding in ice water. The time course of rigor mortis was evaluated, using pH, rigor index and mechanical compression tests. The results showed that the three parameters corresponded very well. Percussive stunning resulted in higher initial post-mortem pH (P < 0.01) and a significantly delayed onset of rigor mortis (P < 0.05). Diet significantly affected shelf-life, with fillets from fish fed diets 500 and 1000 having lower TBARS (thiobarbituric acid reactive substances) numbers from day 2 (P < 0.001) and less colour deterioration from day 7 of storage on ice onwards (P < 0.05). These results suggest that an increase in dietary α-tocopheryl acetate before slaughter as well as careful selection of the slaughtering method may greatly enhance the flesh quality of market-size turbot.