Types of lactic acid
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Types of Lactic Acid: Production and Applications
Introduction to Lactic Acid
Lactic acid is a versatile organic compound with significant industrial applications. It is produced primarily through microbial fermentation, utilizing various microorganisms and carbohydrate sources. The compound exists in two stereoisomeric forms, L-(+)-lactic acid and D-(-)-lactic acid, each with distinct applications in different industries.
Microorganisms Producing Lactic Acid
Lactic Acid Bacteria (LAB)
Lactic acid bacteria (LAB) are the primary producers of lactic acid. These Gram-positive bacteria, including species like Lactobacillus, are known for their efficient fermentation capabilities. LAB can produce lactic acid as the major product during fermentation, making them crucial in the food industry for their ability to enhance flavor, nutrition, and shelf life of fermented products.
Genetically Engineered Microorganisms
Genetic engineering has expanded the capabilities of various microorganisms to produce lactic acid. For instance, Corynebacterium glutamicum and E. coli have been genetically modified to enhance lactic acid productivity. These modifications allow the use of unconventional carbon sources, thereby reducing production costs and increasing yield.
Fungi and Yeasts
Fungi such as Rhizopus spp. can metabolize renewable carbon resources and possess amylolytic properties advantageous for lactic acid production. Yeasts, although naturally low producers of lactic acid, have been improved through genetic manipulation to tolerate acidic conditions and enhance production.
Photosynthetic Microorganisms
Microalgae and cyanobacteria represent alternative lactic acid producers. These photosynthetic microorganisms can produce lactic acid without the need for carbohydrate feed, offering a cost-effective production method.
Substrates for Lactic Acid Production
Lactic acid production requires substrates in the fermentation medium. Various carbohydrate sources can be utilized, including plant waste like molasses, starchy materials, lignocellulosic materials from agricultural and forestry residues, and dairy waste supplemented with nitrogen sources . The use of inexpensive substrates is crucial for reducing production costs and making the process economically viable.
Applications of Lactic Acid
Food and Pharmaceutical Industries
Lactic acid is widely used in the food industry for its ability to improve the nutritional value, control intestinal infections, and enhance lactose digestion. The L-(+)-isomer is particularly preferred in food and pharmaceutical applications due to its compatibility with human metabolism.
Biodegradable Polymers
The production of polylactic acid (PLA), a biodegradable polymer, has significantly increased the demand for lactic acid. PLA is a green alternative to petroleum-derived plastics, and the production of optically pure lactic acid is essential for manufacturing high-quality PLA. The D-(-)-isomer is also important for producing thermostable PLA, although its large-scale production has not yet been commercialized.
Conclusion
Lactic acid is a crucial compound with diverse applications across various industries. The production of lactic acid involves a range of microorganisms, including LAB, genetically engineered bacteria, fungi, yeasts, and photosynthetic microorganisms. Utilizing different carbohydrate sources as substrates can significantly reduce production costs. The compound's applications in the food, pharmaceutical, and biodegradable polymer industries highlight its importance and potential for future advancements.
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