Effects Of Medium Optimization And Oxygen Transfer On Fermentation Process Of Sodium Gluconate By Aspergillus Niger

Sodium gluconate is a kind of organic acid salt that is widely used in food and other industries. It was found that medium components had an important influence on the growth and physiological metabolism of Aspergillus niger as well as the yield of gluconate. The response surface methodology was employed to optimize the original recipe of gluconate fermentation medium in shake flasks. The results showed that the optimized shake flask culture medium components were determined as follows: glucose240g/L, KH2PO40.02g/L, urea0.15g/L, MgSO40.21g/L. Under this condition, the conversion rate was82.21%closing to the theoretical value of83.08%. Compared with the initial medium composition of200g/L glucose,0.02g/L KH2PO4, O.lg/L urea,0.2g/L MgSO4, whose conversion of sodium gluconate was only75.25%, it was nearly increased by7%.We also investigated the influence of oxygen transfer on the sodium gluconate fermentation production by Aspergillus niger. The oxygen supply and the mycelia morphology were mainly studied in this research. The results showed that the oxygen levels had major impact on the formation of sodium gluconate. On the case of only increasing agitation, the aeration was kept at0.8vvm, the oxygen supplement could be enhanced significantly, fermentation time was shortened from35.7h to21.4h and yield was improved from72.88%to87.24%with300g/L initial glucose concentration. In contrast, it was observed that by only increasing aeration without elevating the agitation speed, the fermentation time and yield were little affected, which were30.5h and80.76%, respectively closing to the control. As a consequence, combination of increase of agitation and aeration simultaneously could markedly enhance oxygen supplement, thus the best performance was achieved with20.8h for fermentation time and88.47%for yield. Impeller combinations under condition of constant power, oxygen effect was insignificant.The impact of mycelia morphology on sodium gluconate fermentation was also studied in this thesis. By using the quantitative statistics, we found out the number of Aspergillus niger spores of forming each individual pellet, i.e. about13Aspergillus niger spores could form one pellet. The fermentation cycle of HL-FY-13-04-Ⅱ was34h. which was shortened4.5h compared with the fermentation cycle of HL-FY-12-05-Ⅰ strain. The HL-FY-13-04-Ⅱ product yield was73.04%, which was4.3%higher than that of the HL-FY-12-05-I strain. When the external oxygen supply conditions were kept consistent, the average pellet area of HL-FY-13-04-Ⅱ strain was29997in the process of fermentation, however HL-FY-12-05-Ⅰ average pellet area was37416. Because of smaller fungal pellet of HL-FY-13-04-Ⅱ strains, oxygen transfer between mycelia and fermentation broth was accelerated, making the ability of mycelia to utilze oxygen more readily, therefore the rate of consumption of sugar was improved, also fermentation time was shortened and yield of sodium gluconate was elevated.The results of this research can provide theoretical and experimental evidence for large-scale industrial production of sodium gluconate.