The Production Of L-lactic Acid By Self-immobilized Rhizopus Oryzae

Self-immobilized Rhizopus oryzae has the following advantages: no additional carriers, less injury on the mycelia, more stable technology and much higher fermentative strength.By keeping the morphology of Rhizopus oryzae in pellet-form during fermentation, the self-immobilization of Rhizopus oryzae was achieved. After that, the repeated intermittent fermentation by self-immobilized Rhizopus oryzae was exploited. The stability of technology, the kinetics and the theoretics of the mycelial pellet forming were researched. And then, the parameters and the fermentative strength were optimized.The detailed results were as following:1. When the key parameters being glucose 120g/L, NH₄NO₃ 3g/L and the concentration ratio of K⁺ and Na⁺ 1:1, Rhizopus oryzae grew in pellet-form (diameter of 1.0-2.0mm). When the main fermentative parameters were: H₂PO₄^-0.214g/L, ZnSO₄·7H₂O 0.22g/L, MgSO₄·7H₂O 0.25g/L, the inoculation of germs 10%, the time of CaCO₃ addition Oh, the concentration of L-lactic acid could achieve 100.8g/L.2. When the main factors in the medium of the repeated batch were: glucose 80g/L, NH₄NO₃ 3g/L, KH₂PO₄ 0.0378g/L, the conversion rate of glucose was 3.14%/h in the repeated batch. This technics could ferment stablely for 16 batches.3. The kinetic characteristic of the repeated batch: the consumption of glucose and production of L-lactic acid were linearity, and the mycelial pellet could be used stalely and fastly without the time of stagnancy.4. The best preculture medium was glucose 120g/L, (NH₄)₂SO₄ 4g/L, KH₂PO₄ 0.45g/L; the cluturing time was 22h. Using central composite design and response surface method(RSM) analysis, the best fermentative parameters the aeration 0.75L/(L·min), inoculation of germs 11.5% and agitation speed 575 r/min,and the fermentative strength was that: 2.132g/L/hin the first batch and 3.704g/L/hin the repeated batch...