Optimization Of Oxygen Supply Control During The Fermentation Of Sophorolipids Synthesis From Alkane As Substrate And The Study On Physicochemical Properties Of Production

Sophorolipid is one of the most promising biosurfactants,widely used in cosmetics,petroleum,pharmaceutical and other industries.Alkanes are an important component of petroleum hydrocarbons and the main substance of petroleum pollution.Using alkanes to synthesize sophorolipids can not only obtain green and pollution-free high-performance sophorolipids,but also achieve the degradation of alkanes in petroleum pollutants.During the fermentation of sophorolipids,the level of oxygen supply is an important reason that limits the efficient production of sophorolipids.In this paper,C.bombicola ATCC 22214,a model bacterium of the genus Candida,was used to synthesize sophorolipids with unconventional hydrophobic carbon source n-hexadecane.through the fermentation process multi-parameter and metabolic flux analysis,explore the cell synthesis of sophorolipid macro-and micro-metabolism under different oxygen levels Influencing the law,and developing the most suitable oxygen supply strategy,the goal of increasing the production rate,conversion rate and energy consumption of the sophorolipid fermentation process has been achieved.In addition,through preliminary investigations on the structure,physical and chemical properties and biological activities of sophorolipids synthesized with n-hexadecane as a substrate,it is shown that compared with conventional C18 sophorolipids,C16 sophorolipids are used in food,medicine,nanocarriers,etc.The field may have a wider range of uses.The specific research results obtained in this paper are as follows:First,by adjusting the rotation speed of the fermentation process,the low oxygen supply level(OUR approximately 24 mmol/L/h)and high oxygen supply level(OUR approximately 50 mmol/L/h)can be controlled during the sophorolipid synthesis period.Comparing the cell macro-physiological metabolic parameters and key index parameters in the fermentation process,It was found that the yield of sophorolipids under low oxygen supply conditions was 30.5%lower than that under high oxygen supply conditions,and the specific yield of sophorolipids decreased by 39.4%.Moreover,under high oxygen supply conditions,cells use more glucose to participate in the pentose phosphate pathway to provide reducing power for the synthesis of sophorolipids,while alkanes are more involved in the β oxidation pathway to provide acetyl-CoA and energy,as a result,there are differences in metabolic pathways,which are then manifested as differences in RQ at the macro level of the fermentation process.Secondly,through the integrated analysis of the intracellular metabolite map,key enzyme activity and metabolic flux,the mechanism of the effect of oxygen supply on the synthesis of sophorolipid was analyzed from a microscopic point of view.The results show that sophorolipid anabolism related glycolysis,pentose phosphate,and key intermediate metabolite pools in the TCA cycle pathway are all higher than low oxygen levels,indicating that under high oxygen supply conditions the intracellular metabolism of the strain is more active.Further through the calculation of metabolic flux and the analysis of key enzyme activities in the fermentation process,it was found that the oxygen supply level was reduced,and the enzyme activities of P450 monooxygenase and long-chain fatty alcohol oxidase decreased by 71.1%and 74.5%,respectively,which would limit the synthesis of sophorolipids.At the same time,under different oxygen supply conditions,the ratio of glucose and alkanes involved in the synthesis of sophorolipids will be significantly different,and the RQ value can well characterize the utilization of different substrates by cells,so as to monitor intracellularly during the synthesis of sophorolipids,material distribution and suitability of oxygen supply in the fermentation process.The stepwise oxygen supply study found that when the OUR was maintained at 45 mmol/L/h and the RQ value was 0.62,sophorolipids could reach the highest yield of 1.14 g/L/h,while maintaining a relatively higher alkane utilization rate.Under these conditions,the final output of sophorolipids reached 83.8 g/L,the higher oxygen supply group increased by 4.8%,the utilization rate of alkanes increased by 4.5%,and the power input decreased by 8.6%.Finally,by comparing the structure,physicochemical properties and physiological activities of C16 sophorolipids synthesized with n-hexadecane as a substrate and C18 sophorolipids synthesized with conventional oleic acid as a substrate,it is found that although the structural composition of C16 and C18 sophorolipids is similar,they are mainly lactone-type sophorolipids,but C16 sophorolipids show better characteristics in terms of physical and chemical properties and physiological activities.It is manifested as a lower critical micelle concentration.The acid has stronger emulsification,stronger antimicrobial effect on microorganisms,and stronger antioxidant capacity.In summary,C16 sophorolipids have better application prospects in the fields of nanocarriers,antibacterial agents,and cosmetic additives,and sophorolipids synthesized with n-hexadecane have important application value.