Acetic Acid Production from Lactose by an Anaerobic Thermophilic Coculture Immobilized in a Fibrous-Bed Bioreactor
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- 作者：Mylè ; ne Talabardon ; Jean-Paul Schwitzgué ; bel ; Paul Pé ; ringer ; and Shang-Tian Yang
- 刊名：Biotechnology Progress
- 出版年：2000
- 出版时间：December 2000
- 年：2000
- 卷：16
- 期：6
- 页码：1008 - 1017
- 全文大小：238K
- 年卷期：v.16,no.6(December 2000)
- ISSN：1520-6033
文摘
An anaerobic thermophilic coculture consisting of a heterofermentative bacterium(Clostridium thermolacticum) and a homoacetogen (Moorella thermoautotrophica) wasdeveloped for acetic acid production from lactose and milk permeate. The fermentationkinetics with free cells in conventional fermentors and immobilized cells in a recyclebatch fibrous-bed bioreactor were studied. The optimal conditions for the coculturedfermentation were found to be 58 
C and pH 6.4. In the free-cell fermentation, C.thermolacticum converted lactose to acetate, ethanol, lactate, H2 and CO2, and thehomoacetogen then converted lactate, H2, and CO2 to acetate. The overall acetate yieldfrom lactose ranged from 0.46 to 0.65 g/g lactose fermented, depending on thefermentation conditions. In contrast, no ethanol was produced in the immobilized-cell fermentation, and the overall acetate yield from lactose increased to 0.8-0.96 g/glactose fermented. The fibrous-bed bioreactor also gave a higher final acetateconcentration (up to 25.5 g/L) and reactor productivity (0.18-0.54 g/L/h) as comparedto those from the free-cell fermentation (final acetate concentration, 15 g/L; productivity, 0.06-0.08 g/L/h). The superior performance of the fibrous-bed bioreactor wasattributed to the high cell density (20 g/L) immobilized in the fibrous-bed andadaptation of C. thermolacticum cells to tolerate a higher acetate concentration. Theeffects of yeast extract and trypticase as nutrient supplements on the fermentationwere also studied. For the free-cell fermentation, nutrient supplementation wasnecessary for the bacteria to grow in milk permeate. For the immobilized-cellfermentation, plain milk permeate gave a high acetate yield (0.96 g/g), although thereactor productivity was lower than those with nutrient supplementation. Balancedgrowth and fermentation activities between the two bacteria in the coculture areimportant to the quantitative conversion of lactose to acetic acid. Lactate and hydrogenproduced by C. thermolacticum must be timely converted to acetic acid by thehomoacetogen to avoid inhibition by these metabolites.
C and pH 6.4. In the free-cell fermentation, C.thermolacticum converted lactose to acetate, ethanol, lactate, H2 and CO2, and thehomoacetogen then converted lactate, H2, and CO2 to acetate. The overall acetate yieldfrom lactose ranged from 0.46 to 0.65 g/g lactose fermented, depending on thefermentation conditions. In contrast, no ethanol was produced in the immobilized-cell fermentation, and the overall acetate yield from lactose increased to 0.8-0.96 g/glactose fermented. The fibrous-bed bioreactor also gave a higher final acetateconcentration (up to 25.5 g/L) and reactor productivity (0.18-0.54 g/L/h) as comparedto those from the free-cell fermentation (final acetate concentration, 15 g/L; productivity, 0.06-0.08 g/L/h). The superior performance of the fibrous-bed bioreactor wasattributed to the high cell density (20 g/L) immobilized in the fibrous-bed andadaptation of C. thermolacticum cells to tolerate a higher acetate concentration. Theeffects of yeast extract and trypticase as nutrient supplements on the fermentationwere also studied. For the free-cell fermentation, nutrient supplementation wasnecessary for the bacteria to grow in milk permeate. For the immobilized-cellfermentation, plain milk permeate gave a high acetate yield (0.96 g/g), although thereactor productivity was lower than those with nutrient supplementation. Balancedgrowth and fermentation activities between the two bacteria in the coculture areimportant to the quantitative conversion of lactose to acetic acid. Lactate and hydrogenproduced by C. thermolacticum must be timely converted to acetic acid by thehomoacetogen to avoid inhibition by these metabolites.