Bacteria, heterofermentative

Certain lactic acid bacteria (heterofermentative cocci and homofermentative bacilli) degrade citric acid. Among the species found in wine, L. plantarum, L. casei, O. oeni and L. mesenter-oides rapidly use citric acid. Strains of the genus Pediococcus and of the species L. hilgardii and L. brevis cannot. 

The primary function of cheese starter cultures is to produce lactic acid at a predictable and dependable rate. The metabolism of lactose is summarized in Figure 10.12. Most cheese starters are homofermentative, i.e. produce only lactic acid, usually the L-isomer Leuconostoc species are heterofermentative. The products of lactic acid bacteria are summarized in Table 10.4. 

Figure 13.4 The phosphoketolase pathway used by heterofermentative lactic acid bacteria. (Adapted from Stanier et al. 1970 and Gottschalk 1979.)...

Mellerick, D. and Cogan, T. M. 1981. Induction of some enzymes of citrate metabolism in Leuconostoc lactis and other heterofermentative lactic acid bacteria. J. Dairy Res. 48, 497-502. 

MANNITOL PRODUCTION BY HETEROFERMENTATIVE LACTIC ACID BACTERIA 393... 

Several heterofermentative LAB belonging to the genera Lactobacillus, Leu-conostoc, and Oenococcus can produce mannitol from fructose effectively (Saha, 2003). In addition to mannitol, these bacteria may produce lactic acid, acetic acid, carbon dioxide, and ethanol. The process is based on the ability of the LAB to use fructose as an electron acceptor and reduce it to mannitol with the participation of the enzyme mannitol 2-dehydrogenase (EC 1.1.1.38). 

Several heterofermentative LAB produce mannitol in large amounts, using fructose as an electron acceptor. Mannitol produced by heterofermentative bacteria is derived from the hexose phosphate pathway (Soetaert et al., 1999 Wisselink et al., 2002). The process makes use of the capability of the bacterium to utilize fructose as an alternative electron acceptor, thereby reducing it to mannitol with the enzyme mannitol dehydrogenase. In this process, the reducing equivalents are generated by conversion of one-third fructose to lactic acid and acetic acid. The enzyme reaction proceeds according to (theoretical) Equation 21.1 ... 

Figure 21.2. Pathway of glucose and fructose (1 2) metabolism by heterofermentative lactic acid bacteria.

Racine, E, and Saha, B. C. 2006. Fed-batch and continuous production of mannitol by a heterofermentative lactic acid bacteria. In McKeon, M., and Barton, F. II (Eds.), Proc. United States—Japan Cooperative Program in Natural Resources Food and Agriculture Panel Meeting, Sonoma, CA (pp. BT13-BT17). 

The fermentative production of lactic acid from carbohydrates has repeatedly been reviewed recently [36, 41, 42]. Two classes of lactic acid producers are discerned the homofermentative lactic acid bacteria, which produce lactic acid as the sole product, and the heterofermentative ones, which also produce ethanol, acetic acid etc. [43]. Recently, the focus has been on (S)-L-lactic acid producing, homofermentative Lactobacillus ddbrueckii subspecies [42]. 

There is no available method to remove this taint effectively (Lay 2004). The removal of precursors (L-lysine and ethanol) is not feasible. As it depends on microbial activity, the preventive measures are similar to those suggested for volatile phenols when there is the risk of D. bruxellensis infection. The prevention of spoilage by heterofermentative lactic bacteria usually advised, like decreasing wine pH values and rapid inactivation by sulphur dioxide, once malolactic conversion is finished, should also be effective against bacterial mousiness. 

Production of organic acids is found among various bacterial and fungal species. This is particularly common among all lactic acid bacteria (LAB) (Vesterlund et al., 2004). Heterofermentative LAB are able to ferment various organic acids, predominantly citrate, malate, and pyruvate (Zaunmuller et al., 2006). In various species and strains of LAB, organic acid production may, however, vary. For example, in Lactococcus ladus pyruvate is partially converted to a-acetolactate when electron acceptors (such as citrate) are present, whereas Lactobacillus sanfranciscensis... 

Many names have been assigned to the lactic acid bacteria associated with brewing. It is probable however that most rod-shaped isolates may be classified as the heterofermentative species Lactobacillus brevis, the homo-fermentative species . casei and L, plantarum, and the homofermentative thermophilic species L. delbrueckii [14]. Cocci are also encountered, notably the homofermentative Pediococcus damnosus. (Less common because they are more sensitive to hop resins are P. pentosaceuslacidilactici. Streptococcus saprophyticus, S. epidermis and Micrococcus varians.) Micrococcus kristinae is however resistant to hop resins and low pH, but requires oxygen for growth [15]. An American report states that many breweries encounter L. brevis, L. plantarum and P. damnosus. When the primary fermentation is complete, Pediococcus continues to grow at the bottom of the fermenter in the deposited yeast [16]. 

The biochemistry of the lactic acid bacteria has received attention [4, 17-20]. Homofermentative strains such as the Pediococci use the glycolytic pathway for the dissimilation of carbohydrates, such as glucose, to yield pyruvic acid. Pyruvic acid acts as a hydrogen acceptor and is converted to lactic acid by means of an NADH-dependent lactic dehydrogenase. It is believed that the homofermentative strains use in addition the hexose monophosphate pathway and possibly a phosphoketolase pathway (Fig. 21.2) when pentoses are degraded. The heterofermentative strains on the other hand lack both aldolase and hexose isomerase, essential for the operation of the glycolytic pathway, while pyruvic acid will not readily function as a... 

The lactic acid accumulated during the production of fermented milks and cheeses, besides the related pH drop, represents the key component for the antimicrobial effect of dairy LAB against many spoilage and/or pathogenic bacteria. On the other hand, in some dairy products, and mainly in vegetable-based fermented foods or in intermediate food products such as sourdough, acetic acid released by facultatively or obli-gately heterofermentative LAB can account for an additive preservative effect related to fermentation. 

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