Digestibility and muscle retention of astaxanthin in Atlantic salmon, Salmo salar, fed diets with the red yeast Phaffia rhodozyma in comparison with synthetic formulated astaxanthin

To elucidate whether astaxanthin plasma concentration, deposition and retention in the muscle (% of ingested dose) and apparent digestibility coefficients (ADC) were influenced by astaxanthin source, triplicate groups of size-graded (initial average weight of 0.69 kg) Atlantic salmon (Salmo salar), individually labelled with PIT-tags were fed two different experimental diets (6 tanks, each containing 20 fish) for 86 days. Two experimental extruded feeds (7.3 mm) were supplemented with approximately 40 mg astaxanthin from the red yeast Phaffia rhodozyma (Ecotone(TM)) or Lucantin(R) Pink (LP), respectively. Technical tests applying light microscopy (LM) compared to scanning electron microscopy (SEM) were used to obtain information on visible structural changes of the R rhodozyma cells during feed processing and digestion. The fish increased its weight by 74% irrespective of dietary treatment. The specific growth rate was 0.64% day(-1) for the experiment, Corresponding to a thermal growth coefficient of 2.15. The feed conversion ratios ranged from 0.96 to 0.98. The final total carotenoid concentration of the muscle was significantly higher (P<0.05) in salmon fed the diet supplemented with P. rhodozyma (2.56 mg kg(-1)) compared to salmon fed the diet supplemented with LP (1.96 mg kg(-1)). The total concentrations of the astaxanthin metabolite idoxanthin were similar in the two treatments, but the composition of the 3',4'-cis and 3',4'-trans glycolic isomers was significantly (P<0.05) affected by treatment (idoxanthin 3',4'-cis-to 3',4'-trans glycolic isomer ratio 0.3 to 1.20 for salmon fed the diets supplemented with P rhodozyma and LP, respectively). The highest retention of dietary astaxanthin was found in the muscle of salmon fed the diet supplemented with R rhodozyma cells (6.3%), and it was 86% higher than for salmon fed the synthetic control astaxanthin. This was reflected by the astaxanthin ADC which was about 64 to 68% in salmon fed the diet supplemented with P. rhodozyma and 38 to 42% in the salmon fed the synthetic control (P<0.05). Plasma and muscle carotenoid concentrations correlated poorly (R-2=0.0007), and indicated that plasma concentration of carotenoids is a relatively weak indicator of muscle concentration for salmon fed diets with similar concentrations of astaxanthin. Microscopy tests revealed that the identification of R rhodozyma cells in complex matrices was more reliable when LM was used compared to SEM. The extruded feed supplemented with Ecotone(TM) contained isolated P rhodozyma cells and was free of cell clusters. Some empty cells could be detected. Semi-quantitative analysis by LM revealed that the number of cells was 2.3- to 4.6-fold higher in faeces samples than in the feed. In the faeces various amounts of astaxanthin were observed in the cells. The majority of cells with little or no astaxanthin showed clearly visible lesions or ruptures in the cell wall. It is concluded that Ecotone(TM) represents a more effective astaxanthin source for pigmentation of Atlantic salmon muscle than LP, but microscopic analysis revealed a potential for further improvement. (C) 2007 Elsevier B.V. All rights reserved.