Breeding Of Strain For Producing Citric Acid By Composite Mutation And Optimization Of Fermentation Conditions And Culture Medium

Aspergillus niger Co827 is a high citric acid producing strain, which has very stable citric acid production, transformation ratio and fermentation time, etc. But comparing with the foreign production level, the citric acid level of fermentation is still low.In this paper, strain for producing citric acid is breeding by composite mutation (the ultraviolet and DES), in order to raise the citric acid production, transformation ratio and single production unit of citric acid, optimization the process of citric acid fermentation of obtained new strain, fulfill industrial test of the new strain.1. By optimization of culture medium of existing production strain including the carbon source, nitrogen source and the concentration of mineral salts, the composition of culture medium of fermentation of start strain is fixed on, and optimization of fermentation conditions.2. The effects of three different mutagens (UV,DES, UV+DES) on the citric acid producing strain Aspergillus niger were studied. It was demonstrated that the effect of composite mutation (the ultraviolet and DES) was more efficient.3. A high citric acid producing strain was obtained through a series of screening in flasks in order to train the strain by using an indicator method for screening in the high citric acid concentration and high concentration of dextrose medium. By optimizing the culture medium (carbon source, nitrogen source, mineral salts, etc.), the optical medium was obtained, and optimization of fermentation conditions. By testing the genetic stability, it was showed that the new strain was stable in the speciality of heredity, and confirmed the curves of the growth and fermentation process.4. Comparing the performance of the start strain and high producing strain through industrial test on 300m3 fermentation tank at different initial concentration of dextrose, it was demonstrated that the new strain GSY-085 was more suitable for the fermentation level at initial concentration 17% of dextrose comparing the start strain SCY-022. And the morphologies of the two strains were compared.