Astaxanthin Formation by the Yeast Phaffia rhodozyma

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Abstract
The production of carotenoid pigments by the yeast P. rhodozyma depended on the culture conditions. Astaxanthin, the primary carotenoid in this yeast, was produced mainly during the exponential phase of growth. The concentration of carotenes in P. rhodozyma remained relatively constant [about 5 .mu.g (g yeast)-1] throughout growth in a 1.5% wt/vol glucose medium, but the xanthophyll concentration increased from 90-406 .mu.g (g yeast)-1 during fermentation. Active xanthophyll synthesis occurred during the period of accelerating growth and after exhaustion of glucose from the growth medium. In media containing more than 1.5% (wt/vol) glucose, yeast and carotenoid yields were considerably reduced. The pH of the medium affected yeast yields and carotenoid production; the optimum pH was 5.0. At pH 3.5, .beta.-zeacarotene accumulated in P. rhodozyma. .beta.-Carotene was the primary carotene in the yeast under all other conditions tested. The optimum temperature for yeast growth and pigment formation was 20-22.degree. C and the best C source was D-cellobiose. O2 was an important substrate for optimum yields of yeast and astaxanthin; under microaerophilic growth conditions, astaxanthin production was drastically decreased and P. rhodozyma accumulated .beta.-carotene and the monoketone echinenone.

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