Breeding Of β-carotene Producer And Optimization Of Fermentation Conditions

The original strain Sporidiobolus pararoseus JD-2 was treated gradually by mutagen, and aβ-carotene producer JD-2-8 was obtained based on metabolic engineering principle. Then, conditions in liquid-state and solid-state fermentation were studied. The work and the main conclutions are as follows:(1) The original strain S. pararoseus JD-2 was treated gradually by UV,MV and DES. Then, it was screened by the resistance to diphenylamine.β-carotene high-producing strain JD-2-8 was got in the end. The total carotenoids were enhanced from 0.21 mg/g dried cell to 0.57 mg/g dried cell before optimization.(2) All the carotenoids in Sporidiobolus pararoseus were carried out quantitative and qualitative analysis by thin-layer chromatography, HPLC, LC-MS and spectral analysis. In the end, we got the results that the main carotenoids in S. pararoseus wereβ-carotene, torularhodin, torulen andγ-carotene, all-transβ-carotene takes up 60% of totalβ-carotene.(3) The culture conditions in liquid were studied. It was found that the optimal medium components were glucose 80 g/L, corn steep liquor 19.92 g/L, KH₂PO₄ 0.96 g/L, MgSO₄·7H₂O 0.54 g/L, and the optimal culturing conditions were pH6.0, 28℃. The optimal DO control mode was 0-16 h DO controlled at 20-30%, 16-72 h at 0-5%. After optimization, the cell biomass could reach 56.32 g/L. The productivity of total carotenoids andβ-carotene was 31.07 mg/L and 18.92 mg/L respectively.β-carotene in total carotenoids was 60.43%.(4) Solid-state fermentation was studied. Optimum composition of culture medium were as follows: the ratio of corn flour, soybean dregs and beer's spent grains was 4:1:1. The optimal culture conditions were as follows: 44.4%of initial moisture content, solid medium volume 30 g/250 mL flask , culture time 108h. After optimization, the productivity of total carotenoids was 54.51 mg/kg dry product. The productivity ofβ-carotene was 27.01 mg/kg dry product. In the end, the composition of amino acids and organic acids of S. pararoseus were analyzed. They may be used as fodder yeast in the future.