| Chlorella is an accepted commercial microalgae strain,which has been widely used in food,health care,sewage treatment.In this project,the effects of different cultivation modes on microalgae biomass,chlorophyll and oil were firstly investigated.Then,the parameters of three-phase-partitioning were optimized to extract microalgae lipid using the collected microalgae biomass from different cultivation modes.Finally,fatty acid composition of the neutral lipids,glycolipids,phospholipids was analyzed and fatty acid composition in sn-2 position of triacylglycerols was examined.The main research contents and results were as follows:(1)Chlorella MBFJNU-1 and Chlorella MBFJNU-17 were selected in this study.The biochemical parameters for four types of microalgae cultivation modes(autotrophic seed-autotrophic cultivation,autotrophic seed-heterotrophic cultivation,autotrophic seed-mixotrophic cultivation and mixotrophic seed-mixotrophic cultivation)by the selected microalgae strains.For the Chlorella MBFJNU-1,results showed that the maximum biomass was 10.61±0.68 g/L under the mixotrophic seed-mixotrophic cultivation mode;in this mode,its content of chlorophyll-a for was 42.84±0.75 mg/L.However,the highest contents of polysaccharides and lipid for Chlorella MBFJNU-1were 6747.84±3.88 mg/L and 1388.87±8.17 mg/L under the autotrophic seed-mixed culture mode.For the Chlorella MBFJNU-17,the mixotrophic seed-mixotrophic cultivation mode attained the highest biomass(9.27±0.15 g/L),oil(1297.12±4.31 mg/L)and polysaccharides(3960.00±2.92 mg/L)contents;while,the autotrophic seed-mixotrophic cultivation mode presented the highest chlorophyll-a content(54.56±3.54 mg/L).In term of the fatty acid composition,it was found that the saturated fatty acid content were higher than 40% for two strains by these four different modes.It was noted that microalgae cells under the mixotrophic seed-mixotrophic cultivation mode tended to synthesize polyunsaturated fatty acids(Chlorella MBFJNU-1,50.73%;Chlorella MBFJNU-17,49.50%).Taken together,the mixotrophic seed-mixotrophic cultivation could be the promisng mode for Chlorella strains with the highest biomass.(2)A green and low-energy method for extracting microalgae lipid was developed using Chlorella biomass,namely,three-phase-partitioning(TPP)method.Afteroptimization,the optimal parameters for TPP to obtain the highest lipid extraction efficiency were: the ratio of material to liquid 1:20(algae powder: buffer),10%(w/v)ammonium sulfate concentration,volume ratio 1:2(suspension: tertiary butyl alcohol),temperature 70 ?.Under the optimal extraction conditions,the highest lipid yield was28.67 g/100 g,using Chlorella MBFJNU-17 powder collected in the autotrophic seed-heterotrophic cultivation mode.(3)The extracted microalgae lipids were used to collect neutral lipids,glycolipids and by phospholipids silica gel column.The main fatty acids for the three lipdic classes were C16:0,C18:0,C18:2 and C18:3 by GC-FID.For the Chlorella MBFJNU-1,the highest saturated fatty acids content of neutral lipid from the autotrophic seed-heterotrophic cultivation mode was 55.42%,while the highest polyunsaturated fatty acid of glycolipids from autotrophic seed-mixotrophic cultivation mode was 53.22%.However,for the fatty acid composition of Chlorella MBFJNU-17,autotrophic seed-mixotrophic cultivation mode gave the greatest saturated fatty acids(54.60%);while,autotrophic seed-autotrophic cultivation mode had the highest polyunsaturated fatty acids(49.59%).In view of the fatty acid composition in the sn-2 position of triacylglycerols(TAGs),the polyunsaturated fatty acid content was 37.16% for Chlorella MBFJNU-1 and32.61% for Chlorella MBFJNU-17 under the mixotrophic seed-mixotrophic cultivation mode.Interestingly,saturated fatty acid contents of Chlorella MBFJNU-1 and Chlorella MBFJNU-17 for autotrophic seed-mixotrophic cultivation mode were 58.46% and54.58%,respectively;which suggested that these two Chlorella-derived TAGs were potential new sources for human milk fat substitutes in food application. |
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