β-Carotene production in sugarcane molasses by a Rhodotorula glutinis mutant

Several wild strains and mutants of Rhodotorula spp. were screened for growth, carotenoid production and the proportion of beta -carotene produced in sugarcane molasses. A better producer, Rhodotorula glutinis mutant 32, was optimized for carotenoid production with respect to total reducing sugar (TRS) concentration and pH. In shake flasks, when molasses was used as the sole nutrient medium with 40 g l(-1) TRS, at pH 6, the carotenoid yield was 14 mg l(-1) and beta -carotene accounted for 70% of the total carotenoids. In a 14-1 stirred tank fermenter, a 20% increase in torulene content was observed in plain molasses medium. However, by addition of yeast extract, this effect was reversed and a 31% increase in beta -carotene content was observed. Dissolved oxygen (DO) stat fed-batch cultivation of mutant 32 in plain molasses medium yielded 71 and 185 mg l(-1) total carotenoids in double- and triple-strength medium, respectively. When supplemented with yeast extract, the yields were 97 and 183 mg l(-1) total carotenoid with a 30% increase in beta -carotene and a simultaneous 40% decrease in torulene proportion. Higher cell mass was also achieved by double- and triple-strength fed-batch fermentation.