Extractabilities of astaxanthin and protein from muscle tissue of Atlantic salmon (Salmo salar) as affected by brine concentration and pH

Carotenoids are associated with proteins in muscle tissues of salmonid fishes. The extractabilities of astaxanthin (3,3'-dihydroxy-beta,beta-carotene-4,4'-dione) and protein from minced muscle of Atlantic salmon (Salmo salar) were investigated using different brine concentrations (0-6 M) and different pHs (4-8) to discover whether they contribute to poor colouration of salmonid fish muscle. The salmon had been fed a diet, containing 55 mg kg(-1) astaxanthin from Xanthophyllomyces dendrorhous, for 12 weeks, and contained 3.9 +/- 0.03 mg carotenoids kg(-1) muscle. The plot of ratios between extracted astaxanthin and protein was bell-shaped with a maximum at pH 7, and was considerably lower in brine (1-6 M NaCl) than in distilled water. Regardless of the NaCl-concentration, the highest extractabilities of protein and astaxanthin were found at pH 6-7. Extractabilities of protein and astaxanthin were highest for NaCl concentrations of 1-4 M. The total amount of proteins extracted with brine correlated well with extracted astaxanthin (R-2=0.82). The amounts of astaxanthin extractable from the mince were in the range 1.6-7.4 and 5.9-21.3% of total carotenoid content, in distilled deionised water and 1.0 M brine, respectively. In conclusion, the use of excess water during dry salting, may dilute salt at the surface and partly contribute to discoloration of salmon products, whereas protein-astaxanthin extraction is expected to be less during injection and brine salting due to the high salt concentration. (C) 2003 Elsevier Ltd. All rights reserved.