Heterofermentative lactic fermentations

Schillinger, U., Boehringer, B., Wallbaum, S., Caroline, L., Gonfa, A., Huch (nee Kostinek), M., et al. (2008). A genus-specific PCR method for differentiation between Leuconostoc and Weissella and its application in identification of heterofermentative lactic acid bacteria from coffee fermentation. FEMS Microbiology Letters, 286, 222-226. 

Phosphoketolase is involved in special types of pentose catabolism of fungi and yeasts, and the central fermentative pathway of commensal heterofermentative lactic acid bacteria. 

Unripe cucumbers, after addition of dill herb and, if necessary, other flavoring spices (vine leaf, garlic or bay leaf), are placed into 4-6% NaCl solution or are sometimes salted dry. Usually, the salt solution is poured on the cucumbers in a barrel and then allowed to ferment and, if necessary, glucose is added. Fermentation takes place at 18-20 °C and yields lactic acid, CO2, some volatile acids, ethanol and small amounts of various aroma substances. Homo-and heterofermentative lactic acid bacteria Uke Lactobacillus plantarum, L. brevis and Pediococ-... 

Figure 8.42 Mechanism of heterofermentative lactic acid bacteria fermentation (P = phosphate residue).

Heterofermentative LAB have the capability to utilize high concentrations of fructose such that the mannitol concentration in the fermentation broth could reach more than 180g/L, which is enough to be separated from the cell-free fermentation broth by cooling crystallization. Lactic and acetic acids can be recovered by electrodialysis (Soetaert et al., 1995). The enzyme mannitol dehydrogenase responsible for catalyzing the conversion of fructose to mannitol requires NADPH (NADH) as cofactor. Thus, it is possible to develop a one-pot enzymatic process for production of mannitol from fructose if a cost-effective cofactor regeneration system can be developed (Saha, 2004). The heterofermentative LAB cells can be immobilized in a suitable support, and... 

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). 

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]. 

Obligately heterofermentative Ferment both hexoses and pentoses by the 6-PG/PK (6-phosphogluconate/phosphoketolase pathway) and produce lactic acid, ethanol/acetic acid, and CO2 (this latter only from hexoses) in the ratio 1 1 1... 

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. 

Typical of the microbial succession in sauerkraut fermentation, the so-called betabacteria (heterofermentative lactobacilli such as U>. brevis with higher acid and salt-tolerance than L. mesenteroides) will gradually dominate the population accompanied by a reduction in viable Leuconostoc numbers. The length of the first two stages of sauerkraut fermentation is determined by the temperature, but typically ranges from 3 to 6 days, and is associated with an increase in lactic acid up to around 1% (Muller, 1988). 

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