Astaxanthin over-producing strains of phaffia rhodozyma, methods for their cultivation and their use in animal feeds

Abstract

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.

What is claimed is:  
     
         1 . A strain of  Phaffia rhodozyma  which produces at least about 3,000 ppm astaxanthin based on dry yeast solids when cultivated under suitable conditions in a volume of nutrient medium of at least about 1500 liters and containing in excess of 4 weight percent yeast solids.  
     
     
         2 . The strain of  claim 1  in which the dry yeast solids are in excess of 6 weight percent.  
     
     
         3 . The strain of  claim 2  in which the volume of nutrient medium is at least about 30,000 liters.  
     
     
         4 . The strain of  claim 3  which produces at least about 4,000 ppm astaxanthin based on dry yeast solids.  
     
     
         5 . The strain of  claim 1  selected from the group consisting of the strains deposited as ATCC-74218, ATCC-74219, ATCC-74220 and ATCC-74221, and its mutants and derivatives which have retained the ability to produce astaxanthin at a level of at least about 3,000 ppm based on dry yeast solids when cultivated under suitable conditions and in a volume of nutrient medium of at least about 1500 liters and containing in excess of 4 weight percent yeast solids.  
     
     
         6 . An improved fermentation method for the production of astaxanthin from a strain of  Phaffia rhodozyma,  the method comprising cultivating cells of the strain under suitable conditions in a nutrient medium containing a rapidly metabolized energy source that is maintained over at least part of the cultivation at a level such that the strain experiences (i) a growth phase during which its cells increase rapidly in number and produce astaxanthin, and during which the energy source is fed to the strain at a rate such that it does not accumulate in the medium in excess of a predetermined level, followed by (ii) a maturation phase during which the increase in cell numbers slows but the astaxanthin production continues at a rate at least as great as the rate during the growth phase, the improvement comprising extending the maturation phase.  
     
     
         7 . The method of  claim 6  in which the maturation phase is extended by exposing the strain to a light source.  
     
     
         8 . The method of  claim 7  in which the light source provides light to the strain at less than about 100 watts per kiloliter of fermentation broth.  
     
     
         9 . The method of  claim 8  in which the exposure is essentially continuous from the start of the maturation phase until the termination of the fermentation.  
     
     
         10 . The method of  claim 9  in which the light source provides light to the strain at a wavelength between about 250 and 700 nanometers.  
     
     
         11 . The method of  claim 6  in which the maturation phase is extended by reducing, at the close of the growth phase, the feed rate of the rapidly metabolized energy source to the strain.  
     
     
         12 . The method of  claim 11  in which the feed rate of the energy source is reduced to no more than about 50% of the rate at which the energy source was fed to the strain at the close of the growth phase.  
     
     
         13 . The method of  claim 12  in which the energy source is glucose.  
     
     
         14 . The method of  claim 6  in which the maturation phase is extended by replacing, at the start of the maturation phase, the rapidly metabolized energy source with a slowly metabolized energy source.  
     
     
         15 . The method of  claim 14  in which the rapidly metabolized energy source is glucose, and the slowly metabolized energy source is selected from the group consisting of glycerol; polymerized forms of glucose, sucrose and other polysaccharides found in molasses and corn syrup; monohydric alcohols; and carboxylic acids.  
     
     
         16 . The method of  claim 15  in which the slowly metabolized energy source is fed to the strain with the rapidly metabolized energy source during the growth phase of the fermentation.  
     
     
         17 . The method of  claim 15  in which the slowly metabolized energy source is fed to the strain after the cessation of the rapidly metabolized energy source feed.  
     
     
         18 . Astaxanthin made by the method of  claim 6 .  
     
     
         19 . Astaxanthin made by the method of  claim 7 .  
     
     
         20 . Astaxanthin made by the method of  claim 11 .  
     
     
         21 . Astaxanthin made by the method of  claim 14 .  
     
     
         22 . A  Phaffia rhodozyma  yeast cream made from a strain of  claim 1 .  
     
     
         23 . A dried product made from the yeast cream of  claim 22 .  
     
     
         24 . The dried product of  claim 23  comprising an edible antioxidant, an edible oil, and edible emulsifier.  
     
     
         25 . The dried product of  claim 24  in which the concentration, based on the weight of the dried product, of the antioxidant is between about 0.02 and about 2 weight percent, the oil between about 0.1 and about 10 weight percent, and the emulsifier between about 0.1 and about 10 weight percent.  
     
     
         26 . The dried product of  claim 25  in which the antioxidant is selected from the group consisting of ethoxyquin, vitamin E, ascorbyl palmitate, butylated hydroxyanisole, and butylated hydroxytoluene.  
     
     
         27 . The dried product of  claim 26  in which the oil is selected from the group consisting of safflower oil, corn oil, sunflower oil, soybean oil and blends of two or more of these oils.  
     
     
         28 . The dried product of  claim 27  in which the emulsifier is selected from the group consisting of soy lecithin and sorbitan esters.  
     
     
         29 . The dried product of  claim 23  in which a substantial majority of the yeast cells are unbroken.  
     
     
         30 . The dried product of  claim 29  prepared by spray drying or drum drying the yeast cream.  
     
     
         31 . The dried product of  claim 23  in which a substantial majority of the yeast cells are broken.  
     
     
         32 . The dried product of  claim 31  in which the yeast cells are milled.  
     
     
         33 . An animal feed comprising the dried product of  claim 23 .  
     
     
         34 . An animal feed comprising the dried product of  claim 24 .  
     
     
         35 . The animal feed of  claim 34  comprising between about 0.1 and about 10 weight percent of the dried product, based on the weight of the animal feed.  
     
     
         36 . The animal feed of  claim 34  comprising between about 1 and about 3 weight percent of the dried product, based on the weight of the animal feed.  
     
     
         37 . The animal feed of  claim 35  formulated for an animal selected from the group consisting of salmonid fishes, crustaceans and sea bream fishes.  
     
     
         38 . A method of feeding animals, the method comprising providing the animals with the feed of  claim 23 .  
     
     
         39 . The method of  claim 38  in which the animals are selected from the group consisting of salmonid fishes, crustaceans and sea bream fishes.