Lactococcus dairy fermentations

Lactococcus Common fermenters of dairy products such as cheese Major function is rapid Role in flavor of final product... 

Most polysaccharides used today are of plant origin. However, also bacteria produce polysaccharides. Especially extracellular polysaccharides (eps s) produced by lactic acid bacteria may find application in foods. Lactic acid bacteria are food-grade organisms and the eps s produced offer a wide variety of structures. The presence of eps is considered to contribute greatly to texture and structure of fermented milk products. An exopolysaccharide produced by Lactococcus lactis ssp. cremoris B40 was chosen as a subject of study. The eps was a gift from the Dutch Institute of Dairy Research (NIZO), Ede, the Netherlands. The eps had no gelling properties, could not be precipitated in plates by ethanol or cetylpyridinium chloride and did not show interaction with Congo red. 

Rodriguez-Figueroa, J. C., Gonzalez-Cordova, A. F., Torres-Llanez, M. J., Garcia, H. S., VaUejo-Cordoba, B. (2012). Novel angiotensin I-converting enzyme inhibitory peptides produced in fermented milk by specific wild Lactococcus lactis strains. Journal of Dairy Science, 95, 5536—5543. 

Some species of the LAB group such as Leuconostoc mesenteroides subsp. cremoris, Leuconostoc mesenteroides subsp. dextranicum, and Lactococcus lactis subsp. lactis biovar diacetylactis, are known for their capability to produce diacetyl (2,3-butanedione) from citrate, and this metabolism appears especially relevant in the field of dairy products (Figure 13.4). Actually, selected strains belonging to the above species are currently added as starter cultures to those products, e.g., butter, in which diacetyl imparts the distinctive and peculiar aroma. Nevertheless, in particular conditions where there is a pyruvate surplus in the medium (e.g., in the presence of an alternative source of pyruvate than the fermented carbohydrate, such as citrate in milk or in the presence of an alternative electron acceptor available for NAD+ regeneration) (Axelsson, 2(X)9, pp. 1-72), even other LAB such as lactobacilli and pediococci can produce diacetyl by the scanted pyruvate (Figure 13.5). Thus, in addition to butter and dairy products, diacetyl can be present in other fermented foods and feeds, such as wine and ensilage (Jay, 1982). 

Food preservatives are yet another product of industrial fermentation. Organic acids, particularly lactic and citric acids, are extensively used as food preservatives. Some of these preservatives (such as citric acid) are used as flavoring agents. A mixture of two bacterial species (Lactobacillus and Streptococcus) is usually used for industrial production of lactic acid. The mold Asper Uus niger is used for citric acid manufacturing. Another common preservative is the protein nisin. Nisin is produced via fermentation by the bacterium Lactococcus lactis. It is employed in the dairy industry especially for production of processed cheese. 

Homofermentative lactic acid bacteria (such as Lactococcus lactis and Streptococcus lactis) produce (-l-)-L-lactic acid (e.g. in sour cream). Both isomers, (-l-)-L-lactic acid and (-)-D-lactic acid (8-65), are formed during milk fermentation by heterofermen-tative bacteria (lactic acid bacteria are mostly heterofermentative bacteria) and lactic acid thus also occurs as a racemate in sauerkraut, pickled cucumbers, olives and silage. For example, bacteria of the genus Leuconostoc produce d-lactic acid, while bacteria Pediococcus acidilactici and other bacteria produce racemic lactic acid. The content of lactic acid in dairy products is 0.5-1.0%. L-Lactic acid in yoghurt represents about 54% and in sour cream 96% of the total lactic acid content. The total lactic acid content in sauerkraut is 1.5 2.5%, in fermented cucumbers it ranges from 0.5 to 1.5% and fermented green olives contain 0.8 to 1.2% lactic acid. 

Streptoccocaceae consist of facultatively anaerobic, non-sporing, homofermentative spherical or ovoid cells, typically arranged in chains or pairs. The majority of species belonging to genus Streptococcus are parasitic in man and other animals and the association between some streptococci and a variety of human and animal diseases is established (Hardie and Whiley 1995). On the other hand, members of genus Lactococcus are widely used in the dairy industry due to their ability to produce L(-H)-lactic acid from lactose in spontaneously fermented raw milk at 20-30 °C (Teuber 1995). 

The LAB group is remarkably diverse in their habitats, which are well reflected by their metabolic and transport capabilities. These organisms include the closely related Lactobacillus easel and Lact. brevis, Pediococcuspentosaceus, as well as the more distant Lact. gasseri and Lact. delbrueckii which are often found in plants and their products as well as natural inhabitants of the human gut (Vaughan et al. 2002 Makarova et al. 2006 Lorca et al. 2007). These organisms are used by man for the fermentation of plant, dairy, and meat products. Two other LAB, Lactococcus lactis subspecies cremoris and Streptococcus thermophilus, distantly related to the other LAB but closely related to each other, are both found in milk and are useful for dairy product fermentations. Finally, two additional LAB, closely related to each other but more distantly related to the others, are Leuconostoc mesenteroides, useful for food fermentation purposes, and Oenococcus oeni, important in wine production (Hastings et al. 1991 Mills et al. 2005). 

LeBlanc, J.G., Burgess, C., Sesma, F., et al. (2005b) Ingestion of milk fermented by genetically modified Lactococcus lactis improves the riboflavin status of deficient rats. J Dairy Sci 88, 3435-3442. 

Citrate is present in milk, fruit, and vegetables. It can be co-metabolized with sugars by citrateutilizing LAB. Citrate utilization results in an excess of pyruvate, which is thus converted to diacetyl (2,3-butanedione), acetoin (2-hydroxy-3-butanone), and 2,3-butanediol to equilibrate the redox balance of cellular metabolism (Collins 1972 Bartowsky and Henschke 2004). Some LAB can also synthesize 2,3-pentanedione from pyruvate and threonine (Ott et al. 2000). Diacetyl and 2,3-pentanedione are associated with a buttery aroma, which positively contributes to the flavor of a range of fermented dairy products such as butter (MalUa et al. 2008), yogurt (Routray and Mishra 2011), and cheese (Curioni and Bosset 2002). Diacetyl also contributes to wine style, while it is responsible for flavor defects in beer. Diacetyl is widely produced by LAB, including species of the Lactococcus, Streptococcus, Leuconostoc, Lactobacillus, Pediococcus, and Oenococcus genera. 

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