Utilization of astaxanthin
from red yeast (Phaffia rhodozyma) in Comparison with synthetic
astaxanthin by Atlantic salmon
Trond Storebakken
Akvaforsk, Institute
of Aquaculture Research, AS
Sunndals¿ra, Norway
1998
Abstract:
The aim of the present
study was to compare the efficacy of flesh pigmentation in Atlantic
salmon (Salmo salar), fed diets with astaxanthin from red yeast
(Phaffia rhodozyma) or synthetically produced astaxanthin from
Carophyl Pink. The astaxanthin was incorporated in extruded diets,
aiming at an inclusion rate of 30 or 50 mg kg -1. Each of the
four diets were fed to three groups of 30 individually tagged
Atlantic salmon, kept in saltwater, in an experiment lasting for
12 weeks (2 periods of 6 weeks). Pigmentation of the flesh was
assessed by HPLC, CIE (1976) tristimuli (L*, a*, b*) measurements,
and by Roche color card and SalmoFan. There was considerable variation
in the carotenoid concentration of the diets. The analyzed values
of the two diets with Phaffia were 26 and 47 mg kg-1, while the
two diets with synthetic astaxanthin contained 37 and 61 mg kg
-1 during the first part of the experiment. For the last period
a new diet with he highest concentration of synthetic astaxanthin
was produced, and the average concentrations of astaxanthin were
27 (Phaffia, low), 52 (Phaffia, high) 25 (synthetic, low) and
32 (synthetic, high) mg kg-1, respectively. At the end of the
experiment, 10 salmon from each dietary carotenoid source were
selected, based on similar a* values. One filet from each fish
was taken for 0-time analysis, while the other fillets were salted,
cold smoked, vacuum packed and stored at 4¡ C for 21 d prior to
assessment of carotenoid concentrations and colour. Among the
various procedures used to assess pigmentation, the results obtained
by Colour card, CIE (1976) a* (redness) and SalmoFan had the highest
correlation (R2 from 0.46 to 0.51) to total carotenoid concentration
(astaxanthin + idoxanthin) in the fillets.
The results did not
reveal differences between Phaffia and synthetic astaxanthin in
astaxanthin stability during the extrusion or storage of the feed.
The salmon increases in weight from 0.6 to 1.6 kg during the 12
weeks of feedings. The average feed conversion rate was 0.78 kg
feed per kg gain during the first 6 weeks of feeding, 0.88 kg
kg-1 during the last 6 weeks. The flesh carotenoid concentrations
at the end of the study ranged from 3.3 to 4.3 mg kg-1, with corresponding
colour card, fan and a*-values of 14-15, 25-26 and 7.8-9.5. The
final total carotenoid concentration was higher in the fish fed
the diet with the highest concentration of Phaffia that in the
ones fed the lowest concentration of either of the two carotenoid
sources. The salmon fed the diet with the highest concentration
of synthetic astaxanthin had an intermediate final flesh carotenoid
concentration. The a*-values differentiated significantly among
fish fed those two diets containing the highest concentration
of Phaffia and synthetic astaxanthin and the two diets with the
lower astaxanthin concentrations. The visual colour assessments
only differentiated between the salmon fed the diets with the
highest concentration of Phaffia and the others. The astaxanthin
retention to the flesh ranged from 6 to 11% during the first 6
weeks of feeding and 10 to 16% during the last period. The results
indicate that the retention of astaxanthin was of similar magnitude
for the two carotenoid sources at comparable dietary astaxanthin
concentration. The colour of the flesh did not differ among salmon
pigmented with Phaffia or synthetic astaxanthin.
The overall effect
of smoking and storage was that the total carotenoid concentration
increased by 3-5%, probably due to dehydration during salting
and smoking. The smoking and storage did not result in any significant
change in the proportion of 9-Z or 13-Z-astaxanthin in the flesh.
Lightness (L*) increased when the fillets were smoked. The a*-values
of the surface of the fillets were decreased to half of the initial
value during smoking, and was at an intermediate level after 3
weeks of storage. Yellowness (b*) was increased by 1/3 during
salting and smoking, and also increased as a result of storage,
resulting in a more reddish hue (H¡ ab) of the colour (lower values)
in the raw that in the freshly smoked fillets, while hue of the
stored smoked fillets was intermediate. The hue decreased more
with increasing flesh carotenoid concentration in the smoked and
stored salmon that in the raw fish.
