Lactic acid, microbial synthesis

Lactic acid [50-21-5] (2-hydroxypropanoic acid), CH CHOHCOOH, is the most widely occurring hydroxycarboxylic acid and thus is the principal topic of this article. It was first discovered ia 1780 by the Swedish chemist Scheele. Lactic acid is a naturally occurring organic acid that can be produced by fermentation or chemical synthesis. It is present ia many foods both naturally or as a product of in situ microbial fermentation, as ia sauerkraut, yogurt, buttermilk, sourdough breads, and many other fermented foods. Lactic acid is also a principal metaboHc iatermediate ia most living organisms, from anaerobic prokaryotes to humans. 

Vitamins and Minerals. Milk is a rich source of vitamins and other organic substances that stimulate microbial growth. Niacin, biotin, and pantothenic acid are required for growth by lactic streptococci (Reiter and Oram 1962). Thus the presence of an ample quantity of B-complex vitamins makes milk an excellent growth medium for these and other lactic acid bacteria. Milk is also a good source of orotic acid, a metabolic precursor of the pyrimidines required for nucleic acid synthesis. Fermentation can either increase or decrease the vitamin content of milk products (Deeth and Tamime 1981 Reddy et al. 1976). The folic acid and vitamin Bi2 content of cultured milk depends on the species and strain of culture used and the incubation conditions (Rao et al. 1984). When mixed cultures are used, excretion of B-complex vita-... 

There are many organic acids that can be produced by microbial or biochemical means. However, at present, only acetic acid (as vinegar), citric acid, itaconic acid, gluconic acid, 2-keto-gulonic acid, and lactic acid are produced industrially by fermentation. Other organic acids, such as fumaric, gallic, malic, and tartaric acids, once produced by fermentation or enzyme processes, are now produced commercially, predominantly by the more economic means of chemical synthesis. 

Grbin et al. 2007). ATHP reduction may lead to EHTP. As ethanol is a precursor, mousy off-flavour occurs after alcoholic fermentation, preferably after lactic acid bacteria activity. It seems that the formation of mousiness may be induced by oxidation but it is not clear if the effect is on the microorganisms or in any chemical reaction stimulated by the redox potential. Other agents claimed to affect its production (high pH, low sulphite, residual sugar content) (Lay 2004 Snowdon et al. 2006 Romano et al. 2007) are also stimulators of microbial activity and so the true mechanisms are not yet clarified, but the non-enzymatic chemical synthesis has been ruled out in D. anomala (Grbin et al. 2007). 

Lactic acid can be manufactured by chemical synthesis or microbial fermentation processes. The chemical synthesis process uses petroleum-based chemicals, which are subject to the potential supply problem of crade oil and its dramatic price variation... 

Besides lactic acid. Dr Jun Xu opines that inaeasing demand on biodegradable poly(butylene succinate) (PBS) will open a new market for succinic acid produced via microbial fermentation. He reviews the synthesis of succinic acid, PBS polymerization, crystalline structure, thermal and mechanical properties, and biodegradability. 

Kharas, G., F. Sanchez-Rivera, and D. Severson, Polymers of Lactic Acids, in D. Mobley, Ed., Plastics from Microbes Microbial Synthesis of Polymers and Polymer Precursors, Hanser Pub., Munich, 1994, pp. 93—137. 

Compared with the chemical synthesis, microbial fermentation for lactic acid production is more ecofriendly, comparatively fast, has superior yields, and can produce one of the two stereoisomers of lactic acid as well as their racemic mixture. It is crucial to select the suitable microbes with high productivity, the low-cost raw materials, and most favorable fermentation conditions, for example, temperature, pH, aeration, agitation, and so on. For development of competitive processes, the search for low-cost raw materials... 

Very recently, lactones have received increasing attention as potential renewable platform chemicals. Perhaps the most prominent bio-based hydroxy fatty acids lactic acid, whose cyclic ester of two lactate molecules serves precursor for the synthesis of bio-based polymers. Fermentative production of hydroxyl-carboxylic acids from agro-industrial waste is an alternative to the synthesis from dwindling fossil resources (Fiichtenbusch et al. 2000). The enzymatic machinery for the production of polyhydroxyalkanoates (PHA) in bacteria offers catalytic pathways for the production of these lactone precursors (Efe et al. 2008). Recent examples include the microbial synthesis of y-butyrolactone and y-valerolactone. Particularly y-valerolactone is of importance and ranks among the top key components of the biomass-based economy. Microbial processes thus offer the perspective of a sustainable fermentative production of optically pure renewable lactones. 

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