Production of Organic Acids

Microbial fermentation is favored over chemical synthesis because it is environmentally sustainable and produces enantiomerically pure lactic acid. This biotechnological approach aligns with green chemistry principles while remaining economically viable for industrial applications in food, pharmaceutical, and biodegradable polymer industries.

Starch-rich feedstocks like corn and potatoes are hydrolyzed using either enzymatic hydrolysis with amylases or acid hydrolysis with dilute sulfuric acid. These processes release glucose and other simple sugars that serve as the primary carbon source for microbial fermentation in the bioreactor.

Anaerobic fermentation uses bacteria like Lactobacillus delbrueckii and requires nutrient supplementation including ammonia salts, vitamins, and minerals, typically completing within one to two days. Aerobic fermentation employs molds like Rhizopus oryzae in aerated tanks with minimal nutrient supplementation, also completing within about two days.

Maintaining an optimal pH of 5.5 to 6.5 is essential for microbial activity and lactic acid accumulation. Calcium hydroxide or calcium carbonate is added to neutralize lactic acid as it accumulates, forming soluble calcium lactate and preventing pH from dropping too low, which would inhibit fermentation.

Lactobacillus delbrueckii requires ammonia salts as nitrogen sources, vitamins, and minerals for optimal fermentation. These nutrient supplements support bacterial growth and metabolic activity during anaerobic fermentation at temperatures between 30–45°C, enabling efficient conversion of sugars into lactic acid. Proper designing growth media for bioreactors ensures adequate nutrient availability.

Calcium lactate formed during fermentation is separated and subjected to downstream processing including concentration, filtration, or acidification to recover pure lactic acid. These purification steps isolate the final product from fermentation broth and other byproducts, ensuring product quality for industrial use.

Starch-based substrates like corn and potatoes are abundant, renewable, and cost-effective raw materials. Their widespread availability and sustainability make them ideal for large-scale industrial lactic acid fermentation, supporting economically viable production while aligning with green chemistry principles and reducing environmental impact.