Sucrose lactic acid bacteria

Lactose is readily fermented by lactic acid bacteria, especially Lactococcus spp. and Lactobacillus spp., to lactic acid, and by some species of yeast, e.g. Kluyveromyces spp., to ethanol (Figure 2.27). Lactic acid may be used as a food acidulant, as a component in the manufacture of plastics, or converted to ammonium lactate as a source of nitrogen for animal nutrition. It can be converted to propionic acid, which has many food applications, by Propionibacterium spp. Potable ethanol is being produced commercially from lactose in whey or UF permeate. The ethanol may also be used for industrial purposes or as a fuel but is probably not cost-competitive with ethanol produced by fermentation of sucrose or chemically. The ethanol may also be oxidized to acetic acid. The mother liquor remaining from the production of lactic acid or ethanol may be subjected to anaerobic digestion with the production of methane (CH4) for use as a fuel several such plants are in commercial use. 

The majority of dextrans in nature are produced extracellularly via dextran-sucrase from sucrose by several lactic acid bacteria, principally Leuconostoc and Streptococcus species [13]. Dextran is also synthesised by dextrinase of different Gluconobacter species [56]. Referring to this enzyme, fermentation of maltodextrins leads to a- —4) branched dextrans with comparatively lower Mw. However, dextransucrase from Leuconostoc mesenteroid.es NRRL B-512F has attracted most interest because of commercial use. 

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. 

Dextran is synthesized from sucrose by certain lactic acid bacteria, the best-known being Leuconostoc mesenteroides and Streptococcus mutans. Dextran is also formed by the probiotic Lactobacillus brevis to create the crystals of tibicos or water kefir-fermented beverage with reported health benefits. 

Some lactic acid bacteria have the ability to metabolize sucrose to produce polymers known as dextrans (viscous, slimy). While most strains of Oeno-coccus oeni are negative for this attribute (Edwards et al., 1991), some strains of Lactobacillus (Edwards et al., 1993) and Leuconostoc mesenteroides (Garvie, 1984) are positive. The outlined method originates from Pilone and Kunkee (1972). To test for dextran formation, touch a sterile inoculating needle straight down into an isolated colony and move the needle straight back up. A positive reaction is one where threads or strands are drawn up on the needle. 

Malt wine is made from fermented malt extract (the hot water extract of whole meal malt). Mal-ton wine is made in the same way, except that sucrose is added at 1.8-times the amount of malt in order to increase the sugar and alcohol content of the wine. The wort is then soured by the action of lactic acid bacteria (0.6-0.8% lactic acid, final concentration). The acid fermentation is stopped by heating the wort to 78 °C and, after inoculation with a pure yeast culture, the wort is fermented to an alcohol content of 10-13%. The beverage thus formed has the character of a dessert wine, but is different because of its high content of lactic acid and its malt extract flavor. Mead is an alcoholic liquor made of fermented honey, malt and spices, or just of honey and water (not more than 21 water per kg of honey). Since early times, mead has been widely consumed in Europe and, even today, it is enjoyed the most of all the wine beverages in eastern and northern Europe. 

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