Citrate Acid Production From Cassava

Using Aspergillus niger Wm-01 as original strain, with the high acid contained and highosmotic pressure media as choosing media, a high citric acid producing strain, A. niger Wm-016,from 246 mutants by 60Co-γray, DES and laser compound mutation was selected. In flask with theoptimized fermentation temperature (39±1℃) and period(72h), its average citric yield is 17.2% byusing 22% cassava powder(average sugar content is 17.9%) as main raw material.In 50L automatic fermentor, using filtered cassava liquid as material to produce citric acid, anddiscussing how to control the technical conditions such as pH, temperature and aeration, in order toimprove invert rate and increase citric acid yield. The optimal fermenting condition of Aspergillusniger Wm-016 was 3.0% corn syrup (to complement nitrogen), 16.0% of first sugar in batchfermentation, 12.0% of first sugar in fed-batch fermentation, and 106 spore/mL of inoculate rate.Mg2+ was not need to be added, in that it didn't have something to do with the citric acid yield. Theoptimal content of carbinol was 0.2%, and it had an effect on the yield. Using natural pH in thebeginning. Aspergillus niger Wm-016 can adapt to the high temperature (38~40℃) fermentation. Inthe first 24 hours, the aeration rate was 1:0.12,and in the next 40 hours (to ferment ending) theaeration rate was 1:0.15. In industrial scale fermentor (150m3), its average citric acid yield is 16.1%,and invert rate is 98.5%,while the fermentation period is only 67h.Based the optimized batch-fermentation condition, it was confirmed that the DE of cassavahydrolysate in the fed batch culture was 80, 4% (NH4)2SO4, adding fed batch culture four times 36hours after the fermentation beginning, and 1.5 hours of fed interval, were the optimized fed-batchfermentation conditions, by studying the culture composition, method, original time and interval offed batch, and some main parameters of the citric acid fermentation, such as citric acid yield, invertrate, fermentation periods and residual glucose. In flask with the optimal conditions, the citric acidyield is arrived at 19.0%, and invert rate is 99.2%, while the content of residual glucose is 0.2%,and the fermentation periods is 65 hours.