L-Lactic acid fermentation by culture of Rhizopus oryzae using ammonia as neutralizing agent

Abstract

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±0.05g/hl) and yield (85.3±1.3%) was obtained by culture of R. oryzae BCRC 33071, using 120g/l of glucose as substrate and a mixture of ammonium bicarbonate (2%), urea (1%) and ammonia (10%) as neutralizing agent.