Bacteria, homofermentative

FIGURE 13.3 Schematic illustration of metabolic pathway of glucose in lactic acid bacteria. Homofermentative pathway (a), heterofermentative pathway (b). 

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. 

Mannitol production by homofermentative lactic acid bacteria 392... 

MANNITOL PRODUCTION BY HOMOFERMENTATIVE LACTIC ACID BACTERIA... 

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]. 

Lactic add is a metabohc product of simple carbohydrates produced by many spedes of bacteria, yeasts, and mycehal fungi mainly through the fermentative metabolic pathway. The stoichiometry for homofermentative production of lactic acid from hexose can be expressed as ... 

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... 

Lactic acid bacteria are often described as being either heterofermentative or homofermentative microorganisms. Physiologically, this describes the... 

The reaction in Figure 1.3 takes place in the so-called homofermentative lactic acid bacteria (LAB). Homofermen-tative bacteria have almost exclusively lactic acid as a... 

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