World Aquaculture 31 in the feed but little difference between astaxanthin and canthaxanthin muscle concentration was observed. Optimal concentrations of carotenoids in the feed could lead to a substantial reduction in cost and in better control of the color in the final muscle. In addition, there is more and more evidence that tocopherols and carotenoids are involved in gene regulation and signal transduction thereby affecting the entire metabolism of the animals (Azzi 2007, Lordan et al. 2008). From our feeding trial is seems clear that the oil type, the carotenoids and the level of antioxidants (tocopherols) are directly reflected in the fish muscle composition. Modification of fish metabolic pathways and physiology via feeding regime and in relation to fish muscle composition and subsequent eating quality deserves further attention. Fish Muscle Composition and Oxidative Stability Samples from the feeding trial were stored at -20ºC for 22 months and the quality of the fish muscle was evaluated regularly during the storage period. A series of parameters, including fatty acid profile, free fatty acid content, fish fillet color and antioxidant content were measured throughout the experiment. Oxidation was followed using measurement of both peroxides and volatiles together with sensory evaluation of the fish fillets. Protein oxidation, which is also responsible for some quality changes during storage, was also evaluated using protein carbonyl group measurements. Signs of oxidation were first observed after eight months of storage at -20ºC. However, the entire dataset obtained was compiled in a matrix and a principal component analysis (PCA) was performed to correlate fish muscle composition with oxidative stability during storage. This means that a model was computed to extract the factors responsible for the main variation in the dataset. In Figure 3 the resulting loading plot is given, but for clarity only some of the variable loadings are represented on the plot. Increasing oxidative stability is indicated with the arrow, meaning that variables located on the right of the plot correlate with oxidative stability while variables located on the left correlate with oxidation. Protein, carbonyls and lipid oxidation variables were located together on the left of the plot. Antioxidants were located on the right and clearly contributed to an increased stability of the fish muscle. The tocopherols and canthaxanthin could prevent oxidative deterioration during storage. Canthaxanthin was revealed to be a very good antioxidant and prevented oxidation of the protein during storage, irrespective of the feeding regime. In contrast, astaxanthin’s antioxidant effect was not as clear, inasmuch as our data revealed that it worked sometimes like an antioxidant and sometimes like a prooxidant as seen from its location in the middle of the plot. This is, however, in agreement with the many reports in the literature about the antioxidant effect of carotenoids (Palozza 1998). It is possible that other compounds present in the muscle and/or storage conditions affect astaxanthin’s efficiency in terms of its antioxidant potential. Sensory evaluation results supported our findings. SenFig. 3. PCA of all data from the storage experiment (chemical and sensory analysis) giving the loading plot for the dataset with representation for clarity of only selected attributes loading. [Reprinted and adapted with permission from American Chemical Society 2009, (Baron et al. 2009)]. Fig. 4. PCA for the sensory attribute for rainbow trout fed either fish oil or vegetable oil after 22 months of storage a -4°F (-20°C). With (O) odor, (F) flavor and (T) texture. Bi-plots with scores presented as plain text and loadings in italics. [Reprinted and adapted with permission from American Chemical Society 2009, (Baron et al. 2009)]. sory data of the fish after 22 months of storage were compiled in a PCA ( Figure 4). As in Figure 3, the arrow in Figure 4 indicates an increase in oxidative stability on the right of the plot. The data clearly illustrate that for fish oil fed fish, optimal oxidative stability was obtained for fish oil/ canthaxanthin while the worst combination was obtained for the fish oil/astaxanthin combination. Samples of fish fed vegetable oil were all located on the right of the plot indicating good and similar oxidative stability with only little impact of the presence of carotenoids, which could most likely be attributed to the higher content of tocopherols in the feed. Conclusion Feed composition clearly affected the oxidative sta-
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