| 摘要 |
A yeast cell, preferably a mutant of Phaffis rhodozyma, which, when grown under conditions comprising an oxygen transfer rate of at least 30 mmoles/1/hour on Difco YM medium at 20-22.degree.C for 5 days in 500 ml shake flasks with two baffles containing 50 ml of the medium and subjected to orbital shaking at 150 rpm, the inoculum being 100 .mu.l of a four days old YM culture, produces the red pigment, astaxanthin, in an amount of at least 300 .mu.g per g of yeast dry matter, typically at least 800 .mu.g per g of yeast dry matter, determined by HPLC analysis using pure astaxanthin as a standard on a methanol extract of the yeast prepared by subjecting a suspension of 0.2 g of yeast dry matter in 20 ml of methanol to 5 x 1 minutes of disintegration at intervals of half a minute, the disintegration being performed at a temperature of at the most 20.degree.C in a glass ball mill containing 15 g of glass balls having a diameter of 0.4 mm, the glass ball mill being provided with a cooling jacket with ice water. The amount of astaxanthin produced by the yeast cell, i.e. at least 300 and typically at least 800 .mu.g per g of yeast dry matter, should be compared with the amounts of astaxanthin produced by known Phaffia rhodozyma strains which is at the most about 250 .mu.g per g of yeast dry matter. The mutants of Phaffia rhodozyma may be obtained by conventional methods of mutation. The yeast cells are preferably cultivated by fed-batch fermentation which is performed under sufficient aeration, the fed-batch fermentation preferably comprising a growth phase and a subsequent growth-limited phase. Subsequent to the cultivation, the yeast cells may be subjected to e.g. rupturing and homogenization treatments, and the astaxanthin may optionally be extracted from the yeast cells. The yeast cells or the extracted astaxanthin may be used in animal feed, especially feed for anadromous fish such as salmon or trout, which when being fed with the astaxanthin-containing feed obtain an attractive red colour. |
