Research On Microbial Oils Production By Rhodosporidium Toruloide

In the paper, the utilization of corn stalks hydrolysate for Rhodosporidium toruloides As2.1389 to synthesis microbial oils was explored based on the fermentation of glucose, xylose and mixed sugars, aiming at providing new ideas for raw oils and wastes reuse.First of all, the fermentation of glucose as carbon source with Rhodosporidium toruloides As2.1389 was investigated. The results showed that it was beneficial to the yeasts growth and lipid accumulation when the initial glucose concentration was less than 80 g/L. Compared with inorganic nitrogen, organic nitrogen was more conducive to yeasts growth and lipid accumulation. Ca2+ and Mg2+ were conducive to lipid accumulation, but Zn2+ could inhibit yeasts growth. The strain fermentation conditions were optimized by orthogonal experiment, the results showed that when the shaker speed was 180 r/min and the temperature was 3℃癈, the optimum glucose concentration was 70 g/L, initial pH was 5.0, inoculums was 10% and the volume of liquid was 50 mL. The yield of biomass reached 17.13 g/L, the lipid production was 7.89 g/L, with the lipid content of 46.09% based on dry cell weight.The results of the fermentation of pure xylose in shaker showed that the biomass and the lipid production were far below those with pure glucose as carbon source. The yeasts growth could be inhibited when the initial xylose concentration was more than 40 g/L. When the initial xylose concentration was 40 g/L, inoculums was 10%, fermentation time was 120 h and initial pH was 5.0 with ammonium sulfate and yeast extract as mixed nitrogen source, the yield of biomass reached 12.2 g/L, the lipid production was 4.2 g/L with the lipid content of 34.43% based on dry cell weight.The cofermentation of glucose and xylose with Rhodosporidium toruloides As2.1389 was investigated based on the fermentation of glucose and xylose respectively, the results were much better than the results of fermentation of xylose alone, similar with the results of fermentation of glucose alone. The total concentration of sugar was 80 g/L, H2PO4-concentration was 7.0 g/L, inoculums was 15% and initial pH was 5.0 with yeast extract and ammonium sulfate as nitrogen source. The yield of biomass was 17.4 g/L, the lipid production was 7.0 g/L and the lipid content was 40.23%.Finally, in order to realize the reuse of agricultural wastes, the utilization of lignocelluloses by Rhodosporidium toruloides As2.1389 was investigated. First, the acid hydrolysis under atmospheric pressure and high-pressure were explored respectively with corn stalks. The results showed that the reducing sugar content under high pressure was significantly higher than that under atmospheric pressure. The optimal hydrolysis conditions for corn stalks were 2% H2SO4, solid-to-liquid ratio was 1:10 (g/mL),20 minutes under high pressure in 121℃ and the reducing sugar content was 38.77 g/L. The detoxified hydrolyzates by Ca(OH)2 were well utilized by the yeasts to synthesize biomass. The optimal fermentation conditions were initial pH was 5.0, inoculums was 15%, fermentation time was 120 h. The yield of biomass reached 13.5 g/L, the lipid production was 4.7 g/L, with the lipid content of 34.89% based on dry cell weight. The utilization rate of reducing sugar was 95.73%. The lipid produced by fermentation was characterized by the meteorological chromatography-mass spectrometry analysis, which showed that the composition was similar with vegetable oil. These microbial oils could be further transformed into biodiesel by transesterification.