β-carotene production in sugarcane molasses by a rhodotorula glutinis mutant

Abstract

Several wild strains and mutants of Rhodotorula spp. were screened for growth, carotenoid production and the proportion of β-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 I-1 TRS, at pH 6, the carotenoid yield was 14 mg I-1 and β-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 β-carotene content was observed. Dissolved oxygen (DO) stat fedbatch cultivation of mutant 32 in plain molasses medium yielded 71 and 185 mg I-1 total carotenoids in double-and triple-strength medium, respectively. When supplemented with yeast extract, the yields were 97 and 183 mg I-1 total carotenoid with a 30% increase in β-carotene and a simultaneous 40% decrease in torulene proportion. Higher cell mass was also achieved by double- and triple-strength fed-batch fermentation.