Lactic acid, an important organic acid extensively applied in food, pharmaceutical, and biodegradable polymer industries, is primarily produced via microbial fermentation. This method is favored over chemical synthesis due to its environmental sustainability and capacity for enantiomerically pure product formation. Among various microbial processes, the fermentation of starch-based substrates stands out due to the abundance and renewability of raw materials like corn and potatoes.
Hydrolysis of Starch Substrates:
Starch-rich feedstocks must first be hydrolyzed to release fermentable sugars. This is achieved through enzymatic hydrolysis using amylases or by acid hydrolysis with dilute sulfuric acid. The hydrolysates, rich in glucose and other simple sugars, serve as the primary carbon source for microbial fermentation.
Microbial Fermentation:
Lactic acid fermentation is performed under either anaerobic or aerobic conditions, depending on the microbial strain employed. Bacteria such as Lactobacillus delbrueckii operate under anaerobic conditions and require supplementation with nitrogen sources (e.g., ammonia salts), vitamins, and minerals. These bacteria typically ferment sugars at temperatures between 30–45°C over five to six days. On the other hand, fungi like Rhizopus oryzae perform aerobic fermentation and complete the process within two days, requiring only minimal nutrient supplementation.
pH Control and Product Recovery:
Maintaining an optimal pH of 5.5 to 6.5 during fermentation is critical for microbial activity and lactic acid accumulation. This is managed by the addition of neutralizing agents such as calcium carbonate or calcium hydroxide, leading to the formation of calcium lactate. The calcium lactate is then separated and subjected to purification processes to recover lactic acid in its pure form.
This biotechnological approach to lactic acid production is not only economically viable but also aligns with principles of green chemistry and sustainability.
Organic acids, such as lactic acid, are used in industries including food, medicine, and biodegradable plastics.
Lactic acid is primarily produced by fermenting starch-based substrates like corn or potatoes.
These substrates are first hydrolyzed into simple sugars using amylases or dilute sulfuric acid.
The resulting sugar-rich hydrolysates are then fermented by bacteria or molds in a bioreactor.
Under anaerobic conditions, bacteria such as Lactobacillus delbrueckii produce lactic acid when supplemented with nutrients like ammonia salts, vitamins, and minerals.
Bacterial fermentation typically completes within one to two days under optimal conditions.
Alternatively, molds such as Rhizopus oryzae can ferment sugars in aerated tanks with appropriate nutrients, often completing fermentation within about two days.
As lactic acid accumulates, calcium hydroxide is added to neutralize it, increasing the pH of the medium.
This forms soluble calcium lactate, which is later isolated by concentration, filtration, or acidification during downstream processing.
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