Lactic acid-forming bacteria enantiomers

The method is based on the fact that certain bacteria, fungi, mould or yeast when allowed to grow in a racemic solution, assimilate or consume one of the enantiomers faster than the other. This is why the method is also known as selective assimilation or preferential decomposition. Thus Penicillium glaucum a species of green mould when allowed to grow in ammonium racemate solution consumes the d 0 tartaric acid and leaves the l form, but in a racemic lactic acid it assimilates the l form leaving behind the d form. 

With few exceptions, enzymatic processes in carbohydrates cause degradation. Enzymes are used in the form of pure or semipure preparations or together with their producers, i.e., microorganisms. Currently, semisynthetic enzymes are also in use. Alcoholic fermentation is the most common method of utilization of monosaccharides, sucrose, and some polysaccharides, e.g., starch. Lactic acid fermentation is another important enzymatic process. Lactic acid bacteria metabolize mono- and disaccharides into lactic acid. This acid has a chiral center thus either D(-), L(+), or racemic products can be formed. In the human organism, only the L(+) enantiomer is metabolized, whereas the D(-) enantiomer is concentrated in blood and excreted with urine. Among lactic acid bacteria, only Streptococcus shows specificity in the formation of particular enantiomers, and only the L(+) enantiomer is produced. 

Lactic acid can be formed by either chemical or biological processes. Fermentation processes provide more ability to control the enantiomers being produced. Bacteria have been identified which form both L and D enantiomers. Some preferentially form D, others preferentially form L, and still others form significant amoimts of both enantiomers.The ratio of the two forms in the polymer affects crystallization kinetics, melting temperature, and polymer rheology. L enantiomers are also known to be present in mammalian systems and easily assimilated by humans. ... 

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