L-Lactic Acid Fermentation By Rhizopus Oryzae

In this paper, the fermentation of high optical purified L-lactic acid was conducted by Rhizopus oryzae As3.3462. Effects of carbon resources and its concentration, nitrogen and its concentration, air supply, temperature and pH value on cell growth and on L-lactic acid fermentation were studied in shake flask. Meanwhile, this paper optimized the fermentation in shake flask, which was immobilized by favourable carrier cotton cloth.On the conditions above, the optimal culture condition of immobilized fermentation was also studied in 7L-fermentor. Important results as followins: 1) Optimal compositions of fermentation medium (g/L): corn starch 120, Urea 2.0, KH₂PO₄ 0.3, MgSO₄.7H₂O 0.25, ZnSO₄.7H₂O 0.08. 500mL flask contain 100mL medium, which was cultivated at temp. 30℃and at shaking velocity 180rpm for 72h. The pH was controlled by adding 60g/L sterile CaCO3. On the conditions above, L-lactic acid productivity and the crude corn starch conversion rate were 89.80g/L and 67.74%, respectively. The biomass concentration was 8.8g/L. 2) Immobilization capacity of cotton cloth was found to be preferable performance in cultivation time and L-lactic acid productivity. Favorite productivity of L-lactic acid was induced when the carrier size was about 8¹0mm, concentration of the carrier was 15mL cotton cloth per 50mL seed medium. The L-lactic acid production velocity increased from 1.22 to 1.44g/L·h. 3) A 7L-fermentor immobilized cell fermentation by cotton cloth was developed, the optimal conditions as follows: 7L-fermentor contained 3.5L liquid culture medium; Aeration velocity 0.3L/L·min, rotating speed 50⁸0rpm in pre-20h, aeration velocity 0.6L/L·min, rotating speed 450rpm in 20⁴0h, aeration velocity 0.6L/L·min, rotating speed 500rpm in aft-40h; the fermentation temperature was from32℃to 34℃; pH was from 5.0 to 5.5 and the amout of the defoamer was about 0.1%. On above conditions, L-lactic acid productivity and crude corn starch conversion rate were 88.90/L and 66.74% in 7L fermentor, respectively. The biomass concentration was 7.2g/L. Compare with the same condition fermentation by free cell (1.07g/L·h), L-lactic acid production velocity increase remarkably by immobilized cell technology (1.48g/L·h).