Cheese Starter Cultures

Cogan, Timothy M.; Hill, Colin

doi:10.1007/978-1-4615-2650-6_6

Cited by 97 publications

(69 citation statements)

References 261 publications

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“…actococcus lactis is an industrially important lactic acid bacterium with prominence in the fermented dairy foods industry (3). It is known to convert nearly 90% of simple sugars like glucose into lactic acid at high growth rates (45).…”

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confidence: 99%

Standardized Assay Medium To Measure Lactococcus lactis Enzyme Activities while Mimicking Intracellular Conditions

Goel

Santos

Vos

et al. 2012

Appl Environ Microbiol

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Knowledge of how the activity of enzymes is affected under in vivo conditions is essential for analyzing their regulation and constructing models that yield an integrated understanding of cell behavior. Current kinetic parameters for Lactococcus lactis are scattered through different studies and performed under different assay conditions. Furthermore, assay conditions often diverge from conditions prevailing in the intracellular environment. To establish uniform assay conditions that resemble intracellular conditions, we analyzed the intracellular composition of anaerobic glucose-limited chemostat cultures of L. lactis subsp. cremoris MG 1363. Based on this, we designed a new assay medium for enzyme activity measurements of growing cells of L. lactis, mimicking as closely as practically possible its intracellular environment. Procedures were optimized to be carried out in 96-well plates, and the reproducibility and dynamic range were checked for all enzyme activity measurements. The effects of freezing and the carryover of ammonium sulfate from the addition of coupling enzymes were also established. Activities of all 10 glycolytic and 4 fermentative enzymes were measured. Remarkably, most in vivo-like activities were lower than previously published data. Yet, the ratios of V max over measured in vivo fluxes were above 1. With this work, we have developed and extensively validated standard protocols for enzyme activity measurements for L. lactis.

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confidence: 99%

Standardized Assay Medium To Measure Lactococcus lactis Enzyme Activities while Mimicking Intracellular Conditions

Goel

Santos

Vos

et al. 2012

Appl Environ Microbiol

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“…Lactococcus lactis is widely used as a starter bacterium for the manufacture of Cheddar cheese and other fermented products by the dairy industry (9) and for that reason has attracted intensive research over the last 20 years (1,4,27,70). Lactococci normally contain a rich diversity of plasmids, many of which are responsible for key industrial traits including lactose catabolism, proteinase production, polysaccharide production, bacteriocin production and immunity, and bacteriophage resistance (11,19,20,21,28,39).…”

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Naturally Occurring Lactococcal Plasmid pAH90 Links Bacteriophage Resistance and Mobility Functions to a Food-Grade Selectable Marker

Sullivan

Ross

Twomey

et al. 2001

Appl Environ Microbiol

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. In this communication we provide evidence that the recombination event is favored by phage infection. The entire nucleotide sequence of plasmid pAH90 was determined and found to contain 24 open reading frames (ORFs) responsible for phenotypes which include restriction-modification, phage adsorption inhibition, plasmid replication, cadmium resistance, cobalt transport, and conjugative mobilization. The cadmium resistance property, encoded by the cadA gene, which has an associated regulatory gene (cadC), is of particular interest, as it facilitated the selection of pAH90 in other phage-sensitive lactococci after electroporation. In addition, we report the identification of a group II selfsplicing intron bounded by two exons which have the capacity to encode a relaxase implicated in conjugation in gram-positive bacteria. The functionality of this intron was evident by demonstrating splicing in vivo. Given that pAH90 encodes potent phage defense systems which act at different stages in the phage lytic cycle, the linkage of these with a food-grade selectable marker on a replicon that can be mobilized among lactococci has significant potential for natural strain improvement for industrial dairy fermentations which are susceptible to phage inhibition.Lactococcus lactis is widely used as a starter bacterium for the manufacture of Cheddar cheese and other fermented products by the dairy industry (9) and for that reason has attracted intensive research over the last 20 years (1, 4, 27, 70). Lactococci normally contain a rich diversity of plasmids, many of which are responsible for key industrial traits including lactose catabolism, proteinase production, polysaccharide production, bacteriocin production and immunity, and bacteriophage resistance (11,19,20,21,28,39). Consequently, plasmid mobilization has formed the backbone of numerous strain enhancement regimens to facilitate the transfer of desirable properties into specific bacterial strains that can be employed in fermentations as starter cultures. The conjugal transfer of phage resistance plasmids to phage-sensitive dairy starters has been the focus of considerable research attention (7,23,33,47,51,56). These strategies are aimed at protecting lactococcal strains from the ever-present threat of phage infection during industrial dairy fermentations (16,33,44).Natural phage defense mechanisms such as adsorption inhibition (Ads), injection blocking, restriction/modification (R/ M), and abortive infection (Abi) systems are widespread in lactococci and can coexist and complement each other in cheese-making strains, helping prevent the infection and proliferation of phage (13, 47). However, there are limits to the extent to which natural (food-grade) strategies can be used to introduce and artificially stack phage resistance mechanisms within strains. This is principally because of the paucity of readily selectable markers for phage resistance plasmids, leading to difficulties in recognizing those genuine phage-resistant transconjugants which may arise (47). Antibiotic r...

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“…Lactic acid production is the most important feature of cheese starter cultures, affecting several aspects of cheese manufacture such as coagulant activity, denaturation and retention of the coagulant in the curd during manufacture, curd strength, rheological properties and inhibition of non starter and pathogenic bacteria (Cogan and Daly, 1987). The diversity of cheese varieties is the result of different technologies employed in cheesemaking processes; acidification rate, final pH value and temperature (eg cooking and ripening temperatures) are some of the most criticaJ factors involved.…”

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confidence: 99%

A new approach to the characterization of Streptococcus salivarius subsp thermophilus based on acidification rates

Zanatta

Basso

1992

Lait

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Summary -Thirty-seven strains of Streptococcus salivarius subsp thermophilus, isolated from Italian local chee ses and natural starters were characterized on the basis of 6 parameters of their acidification abilities obtained from pH changes in milk as a function of time. Data were evaluated using principal component analysis (PCA), which emphasized the differences between the strains and allowed them to be divided into 3 groups. The differences observed in the analy1ical procedure were verified in cheesemaking, in which 2 starter cultures composed of strains from 2 different groups were used. Curd acidification rates were different, confirming the validity of the classification. Le pouvoir acidifiant de 37 souches de Streptococcus salivarius subsp thermophilus, isolées de levains naturels et de fromages a été étudié, utilisant 6 paramètres dérivés des courbes d'acidification (pH/temps). Les données ont été traitées par analyse en composantes principales (ACP). Ce traitement, qui a mis en évidence une grande diversité parmi les souches, a permis une répartition des micro-organismes en 3 groupes. Au moyen de quelques essais pratiques en fromagerie les souches des 2 groupes ont été comparées. Il a été remarqué une étroite corrélation entre les différences mises en évidence par le traitement des données et les caractéristiques des fromages produits.

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Cheese Starter Cultures

Cited by 97 publications

References 261 publications

Standardized Assay Medium To Measure Lactococcus lactis Enzyme Activities while Mimicking Intracellular Conditions

Standardized Assay Medium To Measure Lactococcus lactis Enzyme Activities while Mimicking Intracellular Conditions

Naturally Occurring Lactococcal Plasmid pAH90 Links Bacteriophage Resistance and Mobility Functions to a Food-Grade Selectable Marker

A new approach to the characterization of Streptococcus salivarius subsp thermophilus based on acidification rates

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