title: Production of L-lactic acid by Rhizopus oryzae using semicontinuous fermentation in bioreactor.
abstract: Semicontinuous fermentation using pellets of Rhizopus oryzae has been recognized as a promising technology for L-lactic acid production. In this work, semicontinuous fermentation of R. oryzae AS 3.819 for L-lactic acid production has been developed with high L-lactic acid yield and volumetric productivity. The effects of factors such as inoculations, CaCO₃ addition time, and temperature on L-lactic acid yield and R. oryzae morphology were researched in detail. The results showed that optimal fermentation conditions for the first cycle were: inoculation with 4% spore suspension, CaCO₃ added to the culture medium at the beginning of culture, and culture temperature of 32-34 °C. In orthogonal experiments, high L-lactic acid yield was achieved when the feeding medium was (g/l): glucose, 100; (NH₄)₂SO₄, 2; KH₂PO₄, 0.1; ZnSO₄·7H₂O, 0.33; MgSO₄·7H₂O, 0.15; CaCO₃, 50. Twenty cycles of semicontinuous fermentation were carried out in flask culture. L: -lactic acid yield was 78.75% for the first cycle and 80-90% for the repeated cycles; the activities of lactate dehydrogenases (LDH) were 7.2-9.2 U/mg; fermentation was completed in 24 h for each repeated cycle. In a 7-l magnetically stirred fermentor, semicontinuous fermentation lasted for 25 cycles using pellets of R. oryzae AS 3.819 under the optimal conditions determined from flask cultures. The final L-lactic acid concentration (LLAC) reached 103.7 g/l, and the volumetric productivity was 2.16 g/(l·h) for the first cycle; in the following 19 repeated cycles, the final LLAC reached 81-95 g/l, and the volumetric productivities were 3.40-3.85 g/(l·h).
authors.affiliation: School of Biotechnology and Food Engineering, The Key Laboratory for Agricultural Products Processing of Anhui Province, Hefei University of Technology, No. 193 Tunxi Road, 230009 Hefei City, Anhui Province, People's Republic of China. applewuxf@hotmail.com
authors.forename: Xuefeng
authors.initials: X
authors.lastname: Wu
authors.forename: Shaotong
authors.initials: S
authors.lastname: Jiang
authors.forename: Mo
authors.initials: M
authors.lastname: Liu
authors.forename: Lijun
authors.initials: L
authors.lastname: Pan
authors.forename: Zhi
authors.initials: Z
authors.lastname: Zheng
authors.forename: Shuizhong
authors.initials: S
authors.lastname: Luo
mesh_terms: D019149:Bioreactors / Q000382:microbiology*; D002119:Calcium Carbonate / Q000494:pharmacology; D003470:Culture Media; D005285:Fermentation; D007770:L-Lactate Dehydrogenase; D019344:Lactic Acid / Q000096:biosynthesis*; D012233:Rhizopus / Q000166:cytology / Q000378:metabolism*; D013696:Temperature
chemical_list: D003470:Culture Media; D019344:Lactic Acid; D007770:L-Lactate Dehydrogenase; D002119:Calcium Carbonate
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