L(+)-lactic acid production by pellet-form Rhizopus oryzae R1021 in a stirred tank fermentor

• Published in: Chemical engineering science 2003-02, Vol.58 (3-6), p.785-791
• Main Authors: BAI, Dong-Mei, JIA, Min-Ze, ZHAO, Xue-Ming, RUI BAN, FEI SHEN, LI, Xin-Gang, XU, Shi-Min
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Biotechnology; Fundamental and applied biological sciences. Psychology; Methods. Procedures. Technologies; Microbial engineering. Fermentation and microbial culture technology
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/S0009-2509(02)00608-5

L(+)-lactic acid and its salts are widely used in food and pharmaceuticals. Rhizopus oryzae is outstanding in producing optically pure L(+)-lactic acid. Rhizopus cultures can grow as extended filamentous form, mycelial mats, mycelial pellets or clumps which have a significant effect on the rheology of the fermentation broth, which affects the performance of the bioreactor. Factors affecting the morphology and L(+)-lactic acid productivity of R. oryzae R1021 were investigated in detail. Studies on the relationship of CaCO3 addition, inoculum size, concentration of NH4NO3, agitation speed, aeration rate and the morphology of the mycelial growth and lactic acid production were carried out. Uniform sized mycelial pellet growth was obtained when CaCO3 was added 8 h after fermentation. The pellet form exhibited a higher lactic acid yield than clump form. An inoculated spore concentration of 106 spores/ml induced uniform pellets in preculture medium, and then formed the small mycelial pellets in production medium. Maximum L(+)-lactic acid concentration was observed at the inoculum level of 3 x 10(super6) spores/ml. Studies showed that increasing agitation speed caused the pellets to decrease in size and increase in number per unit volume and that increasing aeration rate caused an increase in size and decrease in number.