Impact of dietary carotenoid and packaging during frozen storage on the quality of rainbow trout (Oncorhynchus mykiss) fed carotenoids.

BACKGROUND: The storage life of frozen salmonids is often limited primarily by oxidation and flesh discolouration due to carotenoid degradation. The objective of this research was to determine the carotenoid changes and therefore the muscle colour modifications during 6 months of frozen storage (-18 °C) of whole rainbow trout fed astaxanthin (100 ppm) or canthaxanthin (80 ppm), kept under two different packagings: plastic film and cardboard box. RESULTS: After 6 months of frozen storage, the carotenoid type effect was seen for dry matter while there was no packaging material effect on carotenoid, total lipids, and TBARS contents of trout fillets. The time under frozen storage had an effect on carotenoid and TBARS fillet concentration. The carotenoid-type effect was noted for the four colour parameters (lightness difference, chroma difference, hue angle difference, and total colour difference) of rainbow trout fillet, while the packaging material effect was observed only for chroma. Frozen storage time had an effect on the four colour parameters of rainbow trout fillet. CONCLUSION: Carotenoid and packaging material effects were more marked for colour parameters than for biochemical parameters. In this study, as fish were frozen and stored as whole fish, fish skin provided good protection against oxidation.

Insulin-induced hypoglycaemia is co-ordinately regulated by liver and muscle during acute and chronic insulin stimulation in rainbow trout (Oncorhynchus mykiss).

The relative glucose intolerance of carnivorous fish species is often proposed to be a result of poor peripheral insulin action or possibly insulin resistance. In the present study, data from aortic cannulated rainbow trout receiving bovine insulin (75 mIU kg(-1)) injections show for the first time their ability to clear glucose in a very efficient manner. In another set of experiments, mRNA transcripts and protein phosphorylation status of proteins controlling glycaemia and glucose-related metabolism were studied during both acute and chronic treatment with bovine insulin. Our results show that fasted rainbow trout are well adapted at the molecular level to respond to increases in circulating insulin levels, and that this hormone is able to potentially improve glucose distribution and uptake by peripheral tissues. After acute insulin administration we found that to counter-regulate the insulin-induced hypoglycaemia, trout metabolism is strongly modified. This short-term, efficient response to hypoglycaemia includes a rapid, coordinated response involving the reorganization of muscle and liver metabolism. During chronic insulin treatment some of the functions traditionally attributed to insulin actions in mammals were observed, including increased mRNA levels of glucose transporters and glycogen storage (primarily in the muscle) as well as decreased mRNA levels of enzymes involved in de novo glucose production (in the liver). Finally, we show that the rainbow trout demonstrates most of the classic metabolic adjustments employed by mammals to efficiently utilize glucose in the appropriate insulin context.

Impact of different dietary phospholipid levels on cholesterol and canthaxanthin lipoprotein-serum transport and muscle deposition in rainbow trout.

The study was designed to assess the effect of a progressive increase of dietary phospholipid (PL) levels in the transport of cholesterol and canthaxanthin by serum lipoproteins and their deposition in trout muscle. Three groups of 30 immature rainbow trouts, in triplicate, with a mean body weight of 195 g were fed three experimental diets containing 0, 4, and 8% extra PL contents for 6 weeks. The two major lipoprotein classes in rainbow trout were HDL and LDL. Both lipoproteins were the main transporters of serum canthaxanthin, whereas cholesterol was transported principally by LDL. Serum cholesterol contents remained constant, whereas serum canthaxanthin was increased when the PL amount augmented. In muscle, PL seemed not to have an effect on cholesterol and canthaxanthin deposition. Therefore, as an extra-PL contribution in the diet did not increase relative percentages of cholesterol and/or canthaxanthin in trout muscle, the results support the hypothesis that dietary extra-PL addition is not necessary to increase cholesterol and canthaxanthin and thus fish flesh pigmentation. However, a saturation effect of diet PL contents was found on muscle canthaxanthin deposition.

Effect of soybean phospholipids on canthaxanthin lipoproteins transport, digestibility, and deposition in rainbow trout (Oncorhynchus mykiss) muscle.

This study was designed to assess the effect of dietary soybean phospholipids on canthaxanthin transport by serum lipoproteins and canthaxanthin muscle deposition in trout. Three groups of 12 immature trout in triplicate with a mean body weight of 130 g were fed with three experimental diets containing (1) canthaxanthin plus lecithin plus fish oil, (2) canthaxanthin plus lecithin, and (3) canthaxanthin alone, for 12 days. The two major lipoprotein classes in rainbow trout are high-density lipoproteins, which transport principally carotenoids present in the serum, and low-density lipoproteins, which are responsible for the transport of cholesterol, both independently of the administered diet. In addition, very low density lipoproteins are responsible for triglyceride transport in serum. Nevertheless, the amount of canthaxanthin in the serum increased when carotenoid was associated with phospholipids plus fish oil. When canthaxanthin is transported by lecithin plus fish oil, the amount of phospholipids, cantaxanthin, and cholesterol deposited in muscle increased but not significantly. The highest apparent canthaxanthin digestibility coefficient was obtained when canthaxanthin was carried by lecithin plus fish oil. The administration of canthaxanthin carried by phospholipids improved its accumulation in the muscle of rainbow trout. This accumulation could be enhanced if the time of administration of canthaxanthin is increased.

Carotenoids, mostly the xanthophylls, exchange between plasma lipoproteins.

Carotenoids are exclusively transported by lipoproteins; in vitro studies suggest that they might protect these particles against oxidation. Little is known about the factors that govern the distribution of these micronutrients among lipoproteins. The objective of this study was to assess whether carotenoids are exchanged between lipoproteins and what factors, if any, were involved. In the first experiment, different groups of trout were fed for five days with either a carotenoid-free diet or with diets containing 80 mg pure carotenoid per kilogram of feed. Lipoproteins were separated by ultracentrifugation and carotenoid-rich, high-density lipoproteins (HDL) were incubated for two hours at 37 degrees C with carotenoid-free, very low-density lipoproteins (VLDL), and vice versa. After incubation, lipoproteins were re-separated and carotenoids were quantified to measure the transfer. The same experiments were done in the presence of cholesteryl ester transfer protein (CETP) and lecithin cholesterol acyltransferase (LCAT) inhibitors. In a second experiment, the exchange was measured between human VLDL and HDL. In trout, incubation of carotenoid-rich HDL with carotenoid-free VLDL resulted in the appearance of carotenoids in VLDL, and inversely. The higher the hydrophobicity of a carotenoid, the lower its proportion in HDL after incubation. CETP and LCAT inhibitors significantly increased the proportion of carotenoids in HDL after incubation. Results obtained with human lipoproteins showed that the xanthophyll lutein transferred between lipoproteins, but could not show any carotenes (alpha-carotene, beta-carotene, and lycopene) transfer. We conclude that carotenoids, chiefly the xanthophylls, exchange between lipoproteins. The transfer depends on plasma factor(s) sensitive to CETP and/or LCAT inhibitors.