L-Lactic Acid Fermentation From Corn Starch By Rhizopus Oryzae

Fermentation of high optical purity of L-lactic acid from corn starch was conducted by Rhizopus oryzae As3.3462 .The effects of carbon resources and its concentration,nitrogen and its concentration,air supply,temperature and pH value on cell growth and L-lactic acid fermentation were studied in shake flask.At the same time a method for immobilization of R. oryzae As3.3462 in loofa (Loofa cylindrica) sponge ,cotton cloth and PVA —poly(vinyl alcohol) in shake flask was investigated.Some importants results are as the follows: 1. Loofa sponge as immobilization carrier was better to produce L-lactic acid by R.oryzae As3.3462 compared with PVA and cotton cloth. 2. The optimal compositions of seed medium were as follows(L): glucose 60g;KH2PO4 0.3g; MgSO4.7H2O 0.25g; ZnSO4.7H2O 0.08g; Urea 2g. The number of spores in the suspension was adjusted to 107 per milliliter by dilution with water and the spore suspension was inoculated into a 250ml flask containing 50ml medium and were cultivated at 30℃with shaking at 180r/min for 20h.10g/L CaCO3 autoclaved previously was added to regulate pH.The optimal compositions of fermentation medium were as follows (L): corn starch 120g; Urea 2.0g; KH2PO4 0.3g; MgSO4.7H2O 0.25g; ZnSO4.7H2O 0.08g.The corn starch was liquefied by addition of α-amylase at 85~90 ℃for about 30 min in advance.The fermentation was carried out at 30℃in a 500mL flask containing 100mL medium for 72h.The pH was controlled by adding 60g/L sterile CaCO3,agitation was at 180r/min. On the conditions above,L-lactic acid productivity and the crude corn starch conversion rate were 86.80g/L and 65.17% ,respectively.The biomass concentration was 8.8g/L. 3. Fermentation with loofa (Loofa cylindrica) sponge ,cotton cloth and PVA to be immobilized cell was also studied in shake flask.The immobilization capacity of loofa sponge was found to be preferable to that of PVA and cotton cloth regardless of the cultivation time and L-lactic acid productivity.The productivity of L-lactic aicd was high when the carrier size was about 8～10mm,the concentration of the carrier was 15mL loofa sponge per 50mL seed medium.Results showed that the immobilized cell fermentation circulating six times with loofa sponge was still feasible while the free cell fermentation just two times. The L-lactic acid production velocity had been increased from 1.15 to 1.37g L-lactic acid per litre per hour.It is expected that loofa sponge may be used as an excellent carrier for the immobilization of Rhizopus oryzae.