Microbial production of lactic acid: the latest development

Abstract

Lactic acid is an important platform chemical for producing polylactic acid (PLA) and other value-added products. It is naturally produced by a wide spectrum of microbes including bacteria, yeast and filamentous fungi. In general, bacteria ferment C5 and C6 sugars to lactic acid by either homo- or hetero-fermentative mode. Xylose isomerase, phosphoketolase, transaldolase, l- and d-lactate dehydrogenases are the key enzymes that affect the ways of lactic acid production. Metabolic engineering of microbial strains are usually needed to produce lactic acid from unconventional carbon sources. Production of d-LA has attracted much attention due to the demand for producing thermostable PLA, but large scale production of d-LA has not yet been commercialized. Thermophilic Bacillus coagulans strains are able to produce l-lactic acid from lignocellulose sugars homo-fermentatively under non-sterilized conditions, but the lack of genetic tools for metabolically engineering them severely affects their development for industrial applications. Pre-treatment of agriculture biomass to obtain fermentable sugars is a pre-requisite for utilization of the huge amounts of agricultural biomass to produce lactic acid. The major challenge is to obtain quality sugars of high concentrations in a cost effective-way. To avoid or minimize the use of neutralizing agents during fermentation, genetically engineering the strains to make them resist acidic environment and produce lactic acid at low pH would be very helpful for reducing the production cost of lactic acid.

Nanostructured Metal Catalysts for Selective Hydrogenation and Oxidation of Cellulosic Biomass to Chemicals

“…Lactic acid is another important industrial product, which is conventionally, synthesized via glucose fermentation technologies and widely used in the manufacture of bio‐compatible polymers, environment friendly plastics and non‐BPA food containers (Scheme ) …”

Efficient l‐lactic acid production from purified sweet sorghum juice coupled with soybean hydrolysate as nitrogen source by Lactobacillus thermophilus A69 strain

“…Lactic acid has attracted enormous attention owing to its wide range of industrial applications such as in the food and chemical industries . In addition, optically pure l ‐ and d ‐lactic acids are the main basic ingredients in the synthesis of sustainable and biodegradable plastics, which is an expanding market. In commercial production of lactic acid, microbial fermentation has been considered the strategy with the most potential, the raw materials used being glucose, sucrose or corn starch hydrolysates .…”

Lactobacillus pentosus CECT 4023 T co‐utilizes glucose and xylose to produce lactic acid from wheat straw hydrolysate: Anaerobiosis as a key factor

“…For industrial production, the fermentative process presents several advantages when compared to lactonitrile-based chemical synthesis as the latter uses petrochemical sources which implies environmental concerns. 6 LA can be produced via microbial fermentation using several microorganisms, such as lactic acid bacteria (LAB), yeasts, microalgae, and some Bacillus strains. 6 Most of LA manufacturers use glucose or starchy materials as carbon source supplemented with yeast extract in LA fermentation.…”