| With the rapid depletion of crude resources,microorganism lipids have been getting a lot of attention because of their renewable qualities.In this study,nutrition limitation and high-density fermentation were adopted to realize the high-yield and co-production of lipid and extracellular polysaccharide?EPS?,so the production cost of Sporidiobolus pararoseus JD-2 lipid will be reduced with the higher lipid and EPS yield.The main research results are as follows:?1?After the optimization of nutritional limit and fermentation conditions,it was indicated that nitrogen limitation was the most suitable fermentation strategy for co-production lipid and EPS.The optimized fermentation medium in shake flask contained(g·L-1):glucose 120.0,corn steep liquor?CSL?20,ammonium sulfate 1.2,dipotassium hydrogen phosphate 1.0,sodium sulfate 0.1.The molar ratios of C/N,C/P and C/S in the culture medium were 45,474 and 407 respectively.The fermentation conditions were determined as follows:initial pH 6.0,liquid volume 30 mL,inoculum size 10%,culture temperature 28?.The yields of biomass,lipid and EPS were 51.8±1.6 g·L-1,26.5±0.6g·L-11 and 8.9±0.3 g·L-1 in this condition,which were 35.6%,54.1%and 78.0%higher than control group,respectively.?2?In order to realize high-density fermentation of S.pararoseus JD-2,our study has controlled the severe foam in fed-batch fermentation and has optimized the fed-batch fermentation control strategy.The results showed that the fermentation foam was mainly related to aeration and agitation,protein concentration,cells growth and EPS production.0.1%?v/v?synergistic polyoxymethylene polyoxypropylene pentaerythritol ether?PPE?was pre-added in the culture medium as defoaming agent.Followly,the concentration of corn steep liquor in the culture medium was reduced from 20 g·L-11 to 10 g·L-1,and then 110 g·L-1CSL was fed at the rate of 0.02 L·h-1 for 8-24 h of fermentation to supplement the remaining CSL.Lastly,foam reflux device was connected with the fermentor.Under this condition,the fermentation broth escape volume was successfully reduced from 1.3 L to 0 L.The initial glucose concentration was 60 g·L-1 and maintained at 20 g·L-1 within the whole fermentation period.In addition,the dissolved oxygen concentration was controlled at 20-30%.Under this optimized condition,the yields of lipid and EPS were 67.4±1.6 g·L-1,34.1±0.8 g·L-1 and11.7±0.4 g·L-1,which were 28.6%,31.2%and 28.0%higher than control group,respectively.?3?In order to realize the high-yield and co-production of lipid and EPS under high-density fermentation,the effects of NH4+limitation on the S.pararoseus JD-2fermentation and nutritional limitation composition of the products were studied.The results showed that the yield,productivity and coefficient of lipid reached 47.1±1.1 g·L-1,0.66g·?L·h?-11 and 0.250 g·g-1 during addition of 20 g·L-1 ammonium sulfate,respectively.In the same process,14.3±1.6 g·L-1 EPS and 12.7±0.8 g·L-1 single cell protein?SCP?were also obtained.Compared with the control group without NH4+,the production of the three products was increased by 38.5%,22.22%and 122.8%,respectively.In contrast,the lipid production cost was reduced by 21.8%.Nutrient analysis of the product revealed that when 20 g·L-1ammonium sulfate was added,the carotenoid yield was 24.69±1.18 mg·L-1,and the proportion of unsaturated fatty acids in the fatty acid was 69.69%.EPS was mainly comprised with galactose,glucose,mannose and fucose with a ratio of approximately 45:37:2:1.SCP was composed of 17 kinds of amino acids,and the content of essential amino acid in SCP was48%.?4?In order to comprehensive evaluation the nutritional value of S.pararoseus JD-2,polysaccharide was analyzed.The results showed that 19.4%?w/w?polysaccharide in S.pararoseus JD-2 cells.The intracellular soluble polysaccharide was composed of fucose,galactose,glucose and mannose with a ratio of 1:24:25:2.In addition,the cell wall insoluble polysaccharide was composed of fucose,glucosamine,galactose,glucose and mannose with a ratio of 1:2:7:18:11. |
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