Lipid And Exopolysaccharide Produced By Sporidiobolus Pararoseus

Microbial lipid production has been widely studied from1970 s. High production cost is the limiting factor for the broadly use of microbial lipid. In order to overcome this difficulty, this paper presents a new and cost-efficient route for producing microbial lipid and phosphorylated exopolysaccharides(EPS) simultaneously, which may act as a foundation for the industrialized application of microbial lipid and phosphorylated EPS. The main findings and contents are summarized as follows:(1) Fermentation conditions for microbial lipid and EPS production were optimized, and pointed out that the productions of lipid and EPS were associated with the biomass. In shake-flask fermentation, The highest biomass(58 g/L), lipid(29 g/L) and EPS(8 g/L) productions were obtained at 96 h fermentation with the contents of 126 g/L glucose, 20 g/L corn steep liquor, 10 g/L yeast extract and 2.5 g/L ammonium sulfate. In two-step fed-batch fermentation, the content of ammonium sulfate was controlled between 2.5 g/L to 5 g/L in prophase of fermentation to promote the cell growth, whereas it was controlled at 0 in the later period of fermentation to promote the accumulate of lipid and EPS. At the end of fermentation, the production of biomass, lipid and EPS production were 72 g/L, 39.6 g/L and 12 g/L, respectively. In the fermentation course, the carotenoid accumulating switched to torulene with the content of lipid raised from 20% of dry cell weight(DCW) to 55%.(2) The methods of cell-wall breaking and lipid extraction were optimizated. A proper cell-wall broken method was developed for pilot-scale production using ultrasonic. The predominant lipid-soluble substances in the lipid extracted from S. pararoseus were analyzed, and the main 9 fractions were separated and identified as squalene, ?-carotene, ?-carotene, ergosterol esters, torulene, triglyceride, free fatty acids, ergosterol and torularhodin, respectively. The concentration of ergosterol was about 3.2 g/L in the lipid of S. pararoseus, whereas 16% of the ergosterol exists in the form of ergosterol ester. The concentrations of squalene and carotenoids in the lipid were about 1.25 g/kg and 508 mg/kg. The lipid of S. pararoseus was composed mostly of unsaturated fatty acids, predominantly oleic acid at a level of 73 g per 100 g total fatty acids. Therefore, the lipid of S. pararoseus was proved to be very healthy because it contained not only high oleic acid content but also many functionally fat-soluble nutrients.(3) The molecular weight, molecular diameter, chain structure, monosaccharide composition and constitutional unit of the EPS were detected by high performance size exclusion chromatography, atomic force microscopy, FT-IR spectral analysis, methylation analysis and NMR spectroscopy analysis. The mean molecular weight, hydrodynamic radius(Rh) and mean square radius of gyration(Rg) were approximately 1.3×106, 45 ± 2 nm and 63± 2 nm, respectively. Moreover, the value of Rg/ Rh(1.4) and the ?-value of Mark-Houwink(0.638) indicated that the EPS showed a random coil chain structure, and which was further supported by atomic force microscopy. When analyzing the monosaccharide composition of the EPS, galactose and glucose were found to be the main monosaccharides and the ratio between them was about 2:1, whereas there were no uronic acids. Moreover, the EPS contained approximately 2.1% phosphorus. The constitutional unit indicated that it was a new phosphate diester polysaccharide.(4) Williamson model was used to study the flow character of the EPS solutions in steady shear measurements. When studing the influences of salts on apparent viscosity of EPS, the results pointed out that different NaCl concentrations had little effect on the viscosity of the EPS, but high concentrations of CaCl2 increased the viscosity of EPS significantly. Moreover, the EPS solutions showed inapparent thixotropic properties in thixotropic loop experiment, and showed strong structure reconstruction ability. In oscillation tests, the EPS water solution exhibited as a viscous system. It was found that the increased temperature weaken the thickening properties of EPS solutions. According to the results of flow curve results and oscillatory shear, the rheological properties of EPS solutions were closer to that of flexible random coil system, which like carboxy methyl cellulose rather than weak gel structure such as xanthan gum.(5) The lipid and EPS produced by S. pararoseus were proved having the antioxidant ability and enhance immune functions. Torulene showed the better antioxidant ability than ?-carotene and lycopene based on their abilities to clear ABTS radical, inhibite lipid peroxidation and weak the oxidative damage caused by t-Booh. Moreover, the anticancer and immunological functions of the EPS were also studied, and found that the EPS of S. pararoseus did not directly inhibit the cancer cells, but it had the function to enhance immune functions because it promoted T/B lymphocyte and megalophage proliferations. It was exactly based on this consideration that the EPS of S. pararoseus can be used as pharmacological candidates to enhance immune function.