Search results for "lactococcus lactis"
showing 10 items of 74 documents
Generalized model of the effect of pH on lactate fermentation and citrate bioconversion in Lactococcus lactis ssp. Lactis biovar. diacetylactis
1994
An aroma-imparting mesophilic lactic starter (Lactococcus lactis ssp. lactis biovar. diacetylactis) was studied in batch culture in medium with 50 g·l−1 lactose and 2 g·l−1 citrate. The effect of pH on the physiology of growth and the production of flavour compounds was investigated with a mathematical model. The specific rates of growth and of lactose fermentation obeyed a law of non-competitive inhibition by lactic acid produced, inhibition increasing as the pH of the medium decreased. The pH thus acted indirectly by increasing the proportion of non-dissociated lactic acid, identified as the inhibiting form of lactic acid. The generalized model, taking into account the effect of pH, was t…
Evaluation of microbial diversity during the manufacture of Fior di Latte di Agerola, a traditional raw milk pasta-filata cheese of the Naples area
2006
Microbial diversity of the raw milk for the production of Fior di Latte di Agerola and its changes during cheesemaking were studied. Viable counts showed that at the end of curd ripening, loads of lactic acid bacteria, both mesophilic and thermophilic rods and cocci, higher than those commonly evidenced in similar cheeses produced by using natural or commercial starters, were detected. Identification of 272 isolates, supported by molecular diagnostic aids, evidenced representative cultures of a high number of bacterial taxa of interest as participating in the process, although most of the isolates belonged to Lactococcus lactis and Lactobacillus helveticus species. RAPD-PCR and REA-PFGE bio…
Selected lactic acid bacteria as a hurdle to the microbial spoilage of cheese: Application on a traditional raw ewes' milk cheese
2013
To evaluate the efficacy of lactic acid bacteria (LAB) to improve the hygienic safety of a traditional raw milk cheese, the raw ewes’ milk protected denomination of origin (PDO) Pecorino Siciliano cheese was used as a model system. Different Pecorino Siciliano curds and cheeses were used as sources of autochthonous LAB subsequently used as starter and non-starter LAB. These were screened for their acidification capacity and autolysis. Starter LAB showing the best performance were genotypically differentiated and identified: two strains of Lactococcus lactis subsp. lactis were selected. From the nonstarter LAB, Enterococcus faecalis, Lactococcus garvieae and Streptococcus macedonicus strains…
Transposons Tn916 and Tn925 can transfer from Enterococcus faecalis to Leuconostoc oenos
1996
The streptococcal transposons Tn916 and Tn925 were transferred to several strains of Leuconostoc (Ln.) oenos using the filter mating method. The insertion of both transposons into the chromosome occurred at different sites. Transconjugants of Ln. oenos carrying Tn916 could serve as donors in mating experiments with Lactococcus lactis LM2301. Further analysis of L. lactis LM2301 transconjugants showed that the insertion of the transposon Tn916 into the chromosome was site-specific. These studies establish a basis for the initiation of genetic studies in this Leuconostoc species since there are no efficient conjugal or transformation systems previously described for this microorganism.
Effect of different mineral salt mixtures and dough extraction procedure on the physical, chemical and microbiological composition of Şalgam: A black…
2021
NaCl is utilized in Salgam at 1-2% (w/w). The aim of this study was to reduce the NaCl content by addition of different concentrations of KCl and CaCl2 during production and evaluate their effects on quality. An innovation in production process was also employed, specifically dough extraction and use of the resulting liquid as a starter inoculum. Lactic acid bacteria (LAB) species (13) were identified using a combined approach of (RAPD)-PCR and 16S rRNA gene sequencing. Lactobacillus paracasei and Lactobacillus plantarum were dominant, but Leuconostoc mesenteroides subsp. jonggajibkimchii, Lactococcus lactis subsp. cremoris, Lactobacillus coryniformis subsp. coryniformis, Lactobacillus para…
Understanding of the physiological and genetic mechanisms involved in the reducing activity of Lactococcus lactis
2015
Lactic acid bacteria, particularly Lactococcus lactis are used in dairy industry. These bacteria are known to have a reducing activity, indicating their ability to lower the redox potential (Eh) of a medium. L. lactis MG1363 genome encodes several proteins with a CXXC motif, potentially linked with a redox activity. To understand the role of proteins rich in cysteine located at the surface of L. lactis, two approaches were used, one bioinformatics and biochemical another. For bioinformatic approach, interest was focused on two proteins of unknown function and CX2CX10CX2C motif: Llmg_0524 and Llmg_0526. Their corresponding genes form an operon temporarily induces in early growth phase. In th…
Use of Gases in Microorganism Preservation Processes
2019
International audience
Kinetics of lactate fermentation and citrate bioconversion by LactococcusIactisssp.Iactisin batch culture
1993
The growth kinetics of Lactococcus lactis ssp. lactis were studied in batch culture in conditions of non-limiting lactose and the presence of citric acid. The control of pH modified growth and citrate metabolism but did not change the yield of acid formation. At controlled pH the growth rate was unaffected by citrate metabolism. Lactose was transformed to L-lactate and assay of the metabolic by-products showed some heterofermentation at the end of the growth of cultures with low growth rates. This heterofermentation was interpreted as a slowing down of glycolysis with activation of both the pyruvate formate lyase (PFL) and the pyruvate dehydrogenase complex (PDHC). Under these conditions th…
Comparison of α-acetolactate synthase and α-acetolactate decarboxylase in Lactococcus spp. and Leuconostoc spp.
1994
Cell-free extracts of Leuconostoc and Lactococcus species were tested for their alpha-acetolactate synthase and alpha-acetolactate decarboxylase activities. In Leuconostoc mesenteroides subsp. cremoris, Leuconostoc mesenteroides subsp. mesenteroides and Leuconostoc lactis, the Km of alpha-acetolactate synthase for pyruvate was close to 10 mM whereas it was 30 mM in Lactococcus lactis subsp. lactis biovar. diacetylactis. The Km of alpha-acetolactate decarboxylase for alpha-acetolactic acid was very low (0.3 mM) in Leuconostoc species in comparison to Lactococcus lactis subsp. lactis biovar. diacetylactis (60 mM). In the latter bacterium, alpha-acetolactate decarboxylase showed a sigmoidal de…
Biodiversity and dairy traits of indigenous milk lactic acid bacteria grown in presence of the main grape polyphenols
2020
ABSTRACT The present work was developed to select lactic acid bacteria (LAB) to be used as starter cultures in functional cheese production. The indigenous milk LAB populations were isolated from fermented raw ewes’ milks (four bulks) added with 0.5 mg/mL of nine polyphenols commonly found in winery by-products. After 48 h of fermentation, all milks were characterized by an increase of LAB levels of about 3–4 Log cycles. All different colonies were purified and characterized for the main physiological and biochemical traits and then differentiated genetically at strain level and identified. Ten species belonging to the LAB genera Lactobacillus, Streptococcus, Enterococcus, Leuconostoc and L…