Lactic acid homofermentative

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. 

The most important fermentative reaction used in dairy processing is the homofermentative conversion of lactose to lactic acid. The efficient manufacture of high-quality cultured products, including most cheese varieties, yogurt, and cultured buttermilk, requires a rapid and consistent rate of lactic acid production. Lactic acid helps to preserve, contributes to the flavor, and modifies the texture of these products. Nearly all starter cultures used to produce acidified dairy products contain one or more strains of lactic streptococci, because these organisms can produce the desired acidity without causing detrimental changes in flavor or texture. Strains of lactic streptococci can be classified as... 

Production of lactic acid using whey sometimes is industrially important. In this fermentation the culture of choice is L. bulgaricus because (1) it is homofermentative, producing almost theoretical yields of lactic acid (2) it is thermophilic and, having an optimum growth temperature between 45° and 50 °C, it can be grown in a pasteurized rather than a... 

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]. 

LAB are non-respiring microorganisms, principally generating ATP by fermentation of carbohydrates coupled to substrate-level phosphorylation. The two major pathways for the metabolism of hexoses are homofermentative or glycolysis (Embden-Meyerhof pathway), in which lactic acid is virtually the only end-product, and heterofermentative (phosphoketolase pathway), in which other end-products such as acetic acid, C02, and ethanol are produced in addition to lactic acid (Axelsson et al., 1989 Kandler, 1983 Zourari et al., 1992). 

Efficient lactic acid production from cane sugar molasses is achieved by Lactobacillus delbrueckii in batch fermentation. Fermentative production of lactic acid is very effective in producing optically pure l- or D-lactic and also DL-lactic acid, depending on the strain (Dumbrepatil et al., 2008). Lactobacillus plantarum cells are homofermentative, often used for production of lactic acid from glucose fermentation (Krishnan et al., 2001). 

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 ... 

Using starch as substrate yields were also low. An explanation may be that Streptococcus bovis. a homofermentative lactic acid organism common in the rumen grows rapidly on starch with low yield of biomass (jl). Table n shows some of the results for fermentation of sugar beet pulp (SBP). 

However, the large majority of lactic acid produced today is obtained by bacterial fermentation of simple sugars, using homofermentative strains of the genus Lactobacilli. The homofermentative pathway yields 1.8 moles of lactic acid per mole of hexose, and conversion rates of glucose are higher than 90 %... 

Homofermentative lactobasilli split lactose to glucose and galactose. The glucose is then converted to pyruvate and then to lactic acid with trace amounts of acetic acid and carbon dioxide (Collins, 1977)." Certain species and strains of homofermentative organisms may produce aroma and flavor-enhancing intermediates in addition to lactic acid. 

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... 

LAB belonging to the genera Lactococcus, Enterococcus, Streptococcus, and Lactobacillus are the main representatives responsible for the biopreservation effect in fermented milks and cheeses as based on their homofermentative metabolism of carbohydrate, releasing 2 mol of lactic acid for each mole of glucose consumed. 

Obligately homofermentative Exclusively ferment hexoses and produce lactic acid by the EMP (Embden-Meyerhof-Pamas) pathway... 

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