Image Number 6 for United States Patent #5466599.
Phaffia rhodozyma strains are described which produce greater than 3,000 ppm astaxanthin based on dry yeast solids when cultivated in a volume of nutrient medium of at least about 1,500 liters and containing in excess of 4 percent, preferably in excess of 6 percent, dry yeast solids. These and other strains are cultivated by an improved fermentation method comprising extending the maturation phase of the fermentation by one or more various techniques including exposing the yeast cells to a low-intensity light, slow feeding the cells with a rapidly metabolized energy source, e.g. glucose, and replacing the rapidly metabolized energy source with a slowly metabolized energy source, e.g. gylcerol. The cells of these strains are incorporated into animal feeds, particularly feeds for salmonid fishes, to impart or enhance the red pigmentation of these animals and products made from these animals.