There are two groups of lactic acid bacteria, one is heterofermentative and other is homofermentative. The heterofermentative (e.g. Luconostoc mesenteroides) lactic acid bacteria produce many byproducts other than lactic acid and are not suitable for commercial processes. The homofermentative bacteria (Lactobacillus sp.), very little substrate is used for producing cell mass and other metabolites and majority of the carbon source is converted into lactic acid. In an initial screening, the activities of numerous candidate antimicrobial peptides, made by solid state synthesis, were assessed against several indicator pathogenic E. coli and Salmonella strains.Sugar fermentation followed by a reduction in pH due to the production of lactic and other organic acids is an important factor for the inhibition of growth of undesired microorganisms. The low pH makes organic acids lipossoluble, allowing them to break through the cell membrane and reach the cytoplasm of pathogens . The competition for essential nutrients, accumulation of D-amino-acids and diminution of the oxirredutive potential also contribute to their inhibitory effect.

The effect of lactic acid on the outer membrane permeability of Escherichia coli O157:H7, Pseudomonas aeruginosa, and Salmonella enterica serovar Typhimurium studied utilizing a fluorescent-probe uptake assay and sensitization to bacteriolysis. For control purposes, similar assays were performed with EDTA (a permeabilizer acting by chelation) and with hydrochloric acid, the latter at pH values corresponding to those yielded by lactic acid, and also in the presence of KCN. Already 5 mM (pH 4.0) lactic acid caused prominent permeabilization in each species, the effect in the fluorescence assay being stronger than that of EDTA or HCl. Similar results were obtained in the presence of KCN, except for P. aeruginosa, for which an increase in the effect of HCl was observed in the presence of KCN. The permeabilization by lactic and hydrochloric acid was partly abolished by MgCl2. Lactic acid sensitized E. coli and serovar Typhimurium to the lytic action of sodium dodecyl sulfate (SDS) more efficiently than did HCl, whereas both acids sensitized P. aeruginosa to SDS and to Triton X-100. P. aeruginosawas effectively sensitized to lysozyme by lactic acid and by HCl. Considerable proportions of lipopolysaccharide were liberated from serovar Typhimurium by these acids; analysis of liberated material by electrophoresis and by fatty acid analysis showed that lactic acid was more active than EDTA or HCl in liberating lipopolysaccharide from the outer membrane. Thus, lactic acid, in addition to its antimicrobial property due to the lowering of the pH, also functions as a permeabilizer of the gram-negative bacterial outer membrane and may act as a potentiator of the effects of other antimicrobial substances.

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The KEGG Encyclopedia is a good way to explore biochemical pathways leading to a particular substance. For example, I found this among the 44 pathway results when searching on malate:

http://www.kegg.jp/dbget-bin/www_bget?K07246+1.1.1.83+R00215