In order to avoid the formation of calcium sulfate solid waste in the downstream processing, the
traditional neutralizing agent calcium carbonate used in Rhizopus lactic acid fermentation was replaced
by ammonia water. However, the yield of lactic acid is hampered because of the toxicity of ammonia to
the microbial cells. It is imperative to surmount the dilemma for how to maintain the lactic acid
production but reduce the damage of cells by ammonia. In this work, ammonium bicarbonate and urea
were added to ammonia water to reduce the chemical damage of ammonia on fungal cells. L-Lactic acid
production in an air-lift bioreactor by cultures of R. oryzae BCRC 33071 and ATCC 9363 were compared.
The results showed that the highest productivity (3.01 0.05 g/h l) and yield (85.3 1.3%) was obtained
by culture of R. oryzae BCRC 33071, using 120 g/l of glucose as substrate and a mixture of ammonium
bicarbonate (2%), urea (1%) and ammonia (10%) as neutralizing agent.