| Summary: | Dietary carotenoid (astaxanthin and canthaxanthin) is required for flesh pigmentation of Atlantic salmon and is an expensive component in commercial salmonid feeds. A better understanding of the interaction between astaxanthin and salmon muscle proteins is important to achieve better retention of carotenoid in salmon flesh. This study was undertaken to determine in vitro astaxanthin binding to the muscle proteins of both adult and juvenile Atlantic salmon (Salmo salar), haddock (Melanogrammus aeglefinus ) and halibut (Hippoglossus hippoglossus) for comparison, as well as to investigate membrane bound astaxanthin transport protein(s) in adult salmon using proteomics approach. Several methods such as gel filtration chromatography, fluorometry, immobilization of actin for the binding assay and displacement of hydrophobic probe were examined to assess in vitro astaxanthin binding to salmon muscle actin. None of these methods were found suitable for the binding assays. Astaxanthin binding studies using the gel filtration chromatography or ultrafiltration method were limited by the aggregation of astaxanthin in experimental conditions. An ultrafiltration method was developed for astaxanthin-protein binding assay using 200 mM sodium cholate for dispersion of astaxanthin aggregates based on the 100% passage of dispersed astaxanthin (5.03 muM) through a 30,000 nominal molecular weight limit filter in the presence of 200 mM sodium cholate. Astaxanthin binding to the salmon muscle actin or solubilized fractions of salmon muscle proteins was assessed using the ultrafltration method. The results suggest that proteins other that actin or actomyosin can bind astaxanthin. As well, actin or solubilized fractions of muscle proteins did not show saturation in astaxanthin binding. The characteristics of astaxanthin binding to muscle proteins of salmon, haddock and halibut suggest that carotenoid binding to the muscle proteins do not limit the deposition of carotenoid in salmon flesh. Investigation of membrane bound astaxanthin transport proteins in adult salmon using proteomics approach revealed that proteins were found to be up-regulated in salmon in response to dietary astaxanthin. Mass spectrometry analysis revealed that the up-regulated protein (24-25 kDa) from astaxanthin fed salmon showed extensive homology with the myelin protein zero. Further investigation is necessary to elucidate the transport mechanism of astaxanthin from the blood into the muscle. Thesis (Ph.D.)--Dalhousie University (Canada), 2006.
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