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Propionic acid fermentation of lactose by Propionibacterium acidipropionici: effects of pH
1Department of Chemical Engineering, The Ohio State University Columbus, Ohio 43210, USA.
Insights
Propionibacterium acidipropionici fermentation of lactose yields more propionic acid at lower pH levels. Optimal growth occurs between pH 6.0-7.1, but higher yields are achieved at pH 4.5-5.0.
Area of Science:
- Biotechnology
- Microbial Fermentation
- Industrial Microbiology
Background:
- Propionibacterium acidipropionici is a key bacterium for propionic acid production.
- Lactose fermentation is a significant industrial process.
- Understanding fermentation parameters like pH is crucial for optimizing yields.
Purpose of the Study:
- To investigate the effect of pH on batch fermentation of lactose by Propionibacterium acidipropionici.
- To determine the optimal pH for cell growth and product formation.
- To analyze the yields of major fermentation products, including propionic, acetic, and succinic acids.
Main Methods:
- Batch fermentation of lactose using Propionibacterium acidipropionici.
- Cultivation across a pH range of 4.5 to 7.12.
- Analysis of cell growth rates and fermentation product concentrations.
- Evaluation of yeast extract concentration effects on fermentation.
Main Results:
- Optimal growth rate (0.23 h(-1)) observed between pH 6.0-7.1.
- Propionic acid yield increased significantly at lower pH, reaching 63% (w/w) at pH 4.5-5.0, compared to 33% at pH 6.1-7.1.
- Acetic acid yield remained stable (9%-12%) across pH values.
- Succinic acid yield decreased with decreasing pH, from 17% at pH 7.0 to 8% at pH 5.0.
- Pyruvic acid was an intermediate product, consumed by the end of fermentation.
- Increased yeast extract concentration supported fermentation at acidic pH.
Conclusions:
- Lowering pH from 6.0-7.1 to 4.5-5.0 enhances propionic acid yield from lactose fermentation by P. acidipropionici, despite reduced growth rates.
- Acetic and succinic acid yields are pH-dependent, with succinic acid production decreasing at lower pH.
- Adequate nutrient supply, such as yeast extract, is necessary for efficient fermentation at acidic conditions.
Abstract:
Batch propionic acid fermentation of lactose by Propionibacterium acidipropionici were studied at various pH values ranging from 4.5 to 7.12. The optimum pH range for cell growth was between 6.0 and 7.1, where the specific growth rate was approximately 0.23 h(-1). The specific growth rate decreased with the pH in the acids have been identified as the two major fermentation products from lactose. The production of propionic acid was both growth and nongrowth associated, while acetic acid formation was closely associated with cell growth. The propionic acid yield increased with decreasing pH; It changed from approximately 33% (w/w) at pH 6.1-7.1 to approximately 63% at pH 4.5-5.0. In contrast, the acetic acid yield was not significantly affected by the pH; it remained within the range of 9%-12% at all pH values. Significant amounts of succinic and pyruvic acids were also formed during propionic acid fermentation of lactose. However, pyruvic acid was reconsumed and disappeared toward the end of the fermentation. The succinic acid yield generally decreased with the pH, from a high value of 17% at pH 7.0 to a low 8% at pH 5.0 Effects of growth nutrients present in yeast ex-tract on the fermentation were also studied. In general, the same trend of pH effects was found for fermentations with media containing 5 to 10 g/L yeast extract. However, More growth nutrients would be required for fermentations to be carried out efficienytly at acidic pH levels.
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