Dietary influence on quality of farmed Atlantic cod (Gadus morhua): Effect on glycolysis and buffering capacity in white muscle

The aim was to study the possibility to reduce the pH-drop post mortem in cod muscle by reducing glycolysis or increasing the buffer capacity, hence reducing liquid leakage and fillet gaping during storage. Two feeding experiments were performed with 1-year-old farmed cod (mean weight 0.6 kg–0.9 kg) fed extruded commercial dry feed coated with Experiment 1: sodium oxalate (5 g or 25 g kg− 1), quercetin (5 mg or 25 mg kg− 1), ascorbic acid (1 g or 5 g kg− 1) or magnesium aspartate (5 g or 25 g kg− 1), and Experiment 2: two levels of histidine (12 or 48 g kg− 1), sodium citrate (24 g kg− 1), or a combination of histidine and citrate (12 and 24 g kg− 1, respectively). The cod were kept in duplicate net pens (125 m3) per dietary treatment. In both experiments, samples were collected for analysis after 1 and 3 weeks of feeding. Dietary supplementation with sodium oxalate, quercetin or magnesium aspartate showed no effect on pH, liquid leakage or gaping, whereas the highest level of ascorbic acid gave an unexpected lower pH and higher liquid leakage during cold storage. These results show that the positive health effects commonly obtained by boosting using high levels of ascorbic acid may be counteracted by reduced fillet quality. The feed containing the highest level of histidine gave a significantly higher content of free histidine, higher muscle pH and lower gaping after 3 weeks of feeding. This indicates that dietary histidine accumulates in cod muscle and increases the buffer capacity post mortem. The liquid leakage from raw muscle was, however, not reduced. Surprisingly, the muscle content of anserine (β-alanyl-π-methyl-l-histidine) and other histidine related compounds (1-methyl-histidine, 3-methyl histidine and carnosine) was not affected by the increased dietary histidine. Dietary supplementation of citrate did not significantly alter post mortem muscle pH, gaping or liquid leakage.