A Novel Approach For Sodium Gluconate Production By Enzymatic Catalysis Based On On-line Parameters Association Analysis And The Screening For Strains With High Temperature Tolerance Traits

Sodium gluconate,as a multifunctional derivative of gluconic acid,was widely applied in construction,pharmaceutical,food and water treatment industries.Nowadays sodium gluconate is mainly produced by aerobic submerged fermentation by filamentous fungi such as Aspergillus niger as a producing strain.However,it is well accepted that the sodium gluconate production can be achived by means of adding glucose oxidase and catalase solution.In this paper,we investigated the basic enzymatic parameters and found that the optimal temperature and pH for the glucose oxidase used in production process was 38℃ and 5.2,respectively.Then much attention was paid on the on-line parameters oxygen uptake rate(OUR)and dissolved oxygen(DO).Based on the changing tendency of these parameters,a novel approach of sodium gluconate production was proposed by adding glucose oxidase solution stepwisely,and the activity of glucose oxidase was not the limiting factor any more in the whole production period.The results showed that in the 50L reactor in the presence of 330 g·L-1 initial glucose concentration,the production time was shortened form 17.0h to 11.6h,the yield was enhanced from 1.167(g·g-1)to 1.176(g·g-1)and the overall dosage of glucose oxidase used was reduced from 2100U·g-1 glucose to 1444 U·g-1 glucose respectively.Compared to the biological fermentation,the novel direct enzymatic reaction method displayed significant advantages.The production time was cut down by 42.85%and the yield achieved was 4.91%higher than the traditional conventional fermentation process.The improved direct enzymatic production approach should be more potential in the further industrial application.Considering the rising temperature in the fermentation process due to the insufficient cooling water supplement,it is inevitable for the strains to be degraded for the sodium gluconate production.Consequently,to obtain strains with higher temperature tolerance,a high-throughput screening strategy coupled atmospheric and room temperature plasma(ARTP)and chemostat was established in this study.Based on this strategy,a desired mutation strain II-H7 was successfully screened out.II-H7 showed an almost equal production capability and the yield,which was 1.091(g·g-1),90.17%of the theoretical yield(1.211 g·g-1)when the fermentation temperature was altered from 38℃ to 43℃.The increase of the FI value in fatty acid composition,intracellular proline concentration as well as the change of mycelia morphology were the main possible reasons for the mutant with higher temperature tolerance and high production capability.This work protocol lays a solid foundation for targeted strain evolution and efficient screening.