Production Of L-Lactic Acid By Immobilized Rhizopus Oryzae

The conventional batch fermentation to produce L-lactic acid from glucose by Rhizopus oryzae caused many disadvantages such as long fermentation time, low L-lactic acid yield and unstability of fermentation because of mycelial clumps. On the other side, the immobilized-cell fermentation provided many advantages over conventional fermentation processes, such as shorter fermentation time, higher L-lactic acid yield and reusable ability.The L-lactic acid production by immobilized Rhizopus oryzae in calcium alginate beads and sponge foam were investigated. Results indicated that immobilized cells in calcium alginate beads were reused successfully for more batches (14) than in sponge foam (3). Optimal fermentation technics, fermentation rate and kinetic models of L-lactic acid production by immobilized Rhizopus oryzae in calcium alginate beads were also investigated and the conclusions were as follows:1. The optimal medium for L-lactic acid fermentation were developed by orthogonal design theory.Medium of the 1st batch (g/L): glucose 80, urea 1, potassium dihydrogen phosphate 0.15, zinc sulphate 0.66, magnesium sulphate 0.25.Medium of the 2nd batch (g/L): glucose 80, urea 0.5, potassium dihydrogen phosphate 0.075, zinc sulphate 0.44, magnesium sulphate 0.25.When inoculation of beads was 20%, the culture temperature was 32 ℃, L-lactic acid productivity, conversion rate were 67.5 g/L, 84.4%, respectively after 24h and half fermentation time was decreased by this technique. Results also indicated that immobilized cells were reused successfully for 14 batches and still retained their fermentation activities.2. The effects of the diameter of immobilized cells, inoculation of beads, concentration of glucose and temperature on fermentation rate were investigated. When the diameter of immobilized cells was 2.4mm, the inoculation of beads was 20%, the concentration of glucose was 10-100 g/L, the culture temperature was 32℃, the agitation speed was 80 r/min and the aeration was 1.0 L/Lmin, the productivity could reach 15.5 g/L-h.3. Kinetic models of L-lactic acid production by Rhizopus oryzae were also established. The results showed that the models could describe L-lactic acid fermentation exactly and precisely.