| The multiple morphology of Rhizopus oryzae during the fermentation for L-lactic acid interferes with mass transfer and oxygen dissolution and so makes the fermentation productivity very different. The effect of fermentation condition on the morphology and fermentation yield was investigated. The rheology and oxygen dissolution characteristics for L-lactic acid fermentation of Rhizopus oryzae in pellet and flocs-form were studied; The broth for repeat batch feeding fermentation was fixed and volumetic productivity of pellet and flocs-form Rhizopus oryzae were determined under this fermentation broth; The kinetics of pellet and flocs-form Rhizopus oryzae were studied and the kinetic model was built. The conclusions were listed as follows:1. By single factor and orthogonal tests, main parameters of fermentation broth and fermentation condition for pellet and flocs-form Rhizopus oryzae were obtained:Fermentation broth and fermentation condition for pellet Rhizopus oryzae were: Glucose 120 g/L, (NH4)2SO4 3.0 g/L, KH2PO4 0.15 g/L, MgSO4·7H2O 0.25 g/L, ZnSO4·7H2O 0.25 g/L, NaH2PO4 0.15 g/L, CaCO3 60 g/L, Fermentation temperature 32℃, CaCO3 was added at the beginning of fermentation, Rhizopus oryzae shaped in regular pellet, the production of L-lactic acid fermentation was 104.5 g/L, glucose conversion was 87.08%.Fermentation broth and fermentation condition for Rhizopus oryzae on flocs-form were:Glucose 120 g/L, (NH4)2SO4 3.0 g/L, KH2PO4 0.1 g/L, MgSO4·7H2O 0.25 g/L, ZnSO4·7H2O 0.05 g/L, NaH2PO4 0.25 g/L, CaCO3 60 g/L, Fermentation temperature 32℃, CaCO3 was added at the beginning of fermentation, Rhizopus oryzae shaped in white flocs-form, the production of L-lactic acid fermentation was 104.1 g/L, glucose conversion was 86.75%.2. The rheology and oxygen dissolution characteristics for L-lactic acid fermentation of Rhizopus oryzae in pellet and flocs-form were investigated:The fermentation broth of pellet Rhizopus oryzae were Newton-type fluid with the maxim apparent viscosity 38.6mPa×s; The broths of pellet Rhizopus oryzae in the middle and end phase of fermentation were psedo-plastic fluid with maxim apparent viscosity 108mPa×s;Comparing the critical and practical oxygen dissolution, the rotation speed and oxygen dissolution of Rhizopus oryzae in pellet and flocs-form were adjusted. The practical DO values of Rhizopus oryzae in pellet and flocs-form were 50.5% and 51.3% after adjustment,7.7% and 9.0% more than before adjustment; The acid production were 104.95g/L and 105.75g/L,4.15g/L and 3.95g/L more than before adjustment.3. The feeding medium for repeat batch fermentation was optimized by response surface test.The feeding medium for pellet Rhizopus oryzae were:glucose 90g/L, (NH4)2SO4 3.0g/L, KH2PO4 0.15g/L, MgSO4·7H2O 0.34g/L, ZnSO4·7H2O 0.20g/L;The feeding medium for flocs-form Rhizopus oryzae were:glucose 90g/L, (NH4)2SO4, 3.0g/L, KH2PO4 0.15g/L, MgSO4·7H2O 0.35g/L, ZnSO4·7H2O 0.21 g/Lrespectively; In the first 6 batches, Rhizopus oryzae in pellet form produced the acid at the lever of 80g/L with the yield more than 88.89% and highest fermentative strength 4.26 g·L-1·h-1, in the 7th batches, the production of L-lactic acid was reduced to 78.60 g/L with the yield was 87.3%; while Rhizopus oryzae in flocs-form produced more than 80g/L L-lactic acid in the first 4 batches, and the fermentative strength reached to as high as 4.07 g·L-1·h-1.and the production of L-lactic acid was reduced in the 5th batches, in the 7th batches, the production of L-lactic acid was70.20 with the yield was 78.00%.4. The kinetic parameters were estimated and the kinetic models for L-lactic acid production of pellet and flocs-form Rhizopus oryzae were built: Kinetic models for pellet Rhizopus oryzae:Microbe growth model:Lactic acid production model:Kinetic models for flocs-form Rhizopus oryzae:Microbe growth model:Lactic acid production model:The simulation results suggest that the kinetic models can descript the experimental process well.
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