Showing papers by "Christophe Lacroix published in 1997"
TL;DR: Mutacin B‐Ny266 belongs to the type A lantibiotics and the proposed sequence is: F–K– –W–U–F– – –P–G– –A–K-O–G – –F–N– –Y– .
94 citations
TL;DR: The statistical analysis showed that the three strains were differently affected by the studied parameters, and that a large range of effluent starter composition can be achieved by varying D, pH, and T.
Abstract: The aim of this work was to study a new process for the continuous production of mixed-strain lactic acid bacteria starters using immobilized cells. Three strains of Lactococcus (two Lactococcus lactis subsp. lactis: KB and KBP, and one Lactococcus lactis subsp. lactis biovar diacetylactis: MD) were immobilized separately in kappa-carrageenan-locust bean gum gel beads. Continuous fermentations were carried out in a 1 L pH-controlled stirred tank reactor with a 30% (v/v) bead inoculum (strain ratio 1:1:1), continuously fed with a whey UF permeate medium, supplemented with 1.5% yeast extract and 0.1M KCl. The effects of three parameters-pH, temperature (T), dilution rate (D), and their interactions on the composition and activity of the culture in the effluent at pseudosteady state were studied according to a rotatable central composite design, during a 53-day fermentation. The process showed a high biological stability and no strain became dominant, or was eliminated from the bioreactor. The statistical analysis showed that the three strains were differently affected by the studied parameters, and that a large range of effluent starter composition can be achieved by varying D, pH, and T. However, the acidifying characteristics were not affected by the culture conditions. A cross-contamination from other strains of the mixed culture was observed in gel beads entrapping a pure culture at the fermentation onset, and led to a biomass redistribution within the beads. However, the strain ratio (KB:KBP:MD) observed after the 53-day experiment (1:2:2) was close to the initial bead ratio (1:1:1). The beads demonstrated a high mechanical stability throughout the 53-day continuous fermentation. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 502-516, 1997.
66 citations
TL;DR: The bacteriocin produced by Lactococcus lactis ssp.
Abstract: The bacteriocin produced by Lactococcus lactis ssp. lactis biovar. diacetylactis UL 719 was purified and characterized. Two peaks exhibiting antimicrobial activity were obtained after purification. Primary structure of the peptide of major peak 2 was identical to that of nisin Z when determined by Edman degradation and confirmed by DNA sequence analysis. The molecular mass as determined by mass spectrometry was 3346.39 +/- 0.40 Da for peak 1 and 3330.39 +/- 0.27 Da for peak 2, which suggests that peak 1 may correspond to an oxidized form of nisin Z. The two purified peaks exhibiting antimicrobial activity appear to correspond with oxidized and native forms of nisin Z.
54 citations
TL;DR: An unusual high‐molecular‐mass b‐galactosidase isoenzyme from Thermus aquaticus YT‐1 was purified to homogeneity by chromatography using gel filtration, anion‐exchange and gel Filtration and the thermostability of the enzyme was enhanced by CaCl2.
Abstract: An unusual high-molecular-mass b-galactosidase isoenzyme from Thermus aquaticus YT-1 was purified to homogeneity by chromatography using gel filtration (Ultrogel AcA 34), anion-exchange (Mono Q) and gel filtration (Superose-12). The molecular mass of the purified enzyme was > 700 kDa as estimated by gel filtration, and its subunit molecular mass was 59 ± 1 kDa as determined by SDS/PAGE. A single protein band of pI 4.9 was obtained by isoelectric-focusing gel electrophoresis. The optimum tempera-ture and pH for enzyme activity were 80 ° C and pH 5.5 respectively. The enzyme was stable over a wide pH range (pH 3-12), and the thermostability of the enzyme was enhanced by CaCl2. The enzyme was significantly activated by alkali and alkaline-earth-metal salts. Whereas reducing agents enhanced b-galactosidase activity, thiol-binding agents drastically decreased the enzyme activity. The enzyme was strongly inhibited by the end products of the lactose hydrolysis reaction. The b-galactosidase was specific for b-D anomeric linkages, and the identity of the aglycone moiety also influenced enzyme activity dramatically. Oligosaccharide (OS) formation rates were directly related to lactose concentration. At a concentration of 19.4% (w/v) lactose, OS accounted for approx. 20′ of the total carbohydrates, and only two types of OS were observed. Moreover, once formed, OS were not rehydrolysed to monosaccharides, even during long residence times. OS synthesis was also observed with cellobiose and lactulose. Fructose, xylose, lyxose, rhamnose and arabinose were active as galactosyl acceptors, in contrast with glucose, ribose, fucose, tagatose and N-acetyl-glucosamine.
42 citations
TL;DR: Fifty‐one bacteriocin‐producing bacteria (Bac+) were isolated from 35 raw milk cheeses by the deferred antagonism method using Listeria strains as indicator organisms, showing good capacity for milk acidification decreasing the pH of milk from 6.5 to 4.3.
Abstract: Summary Fifty‐one bacteriocin‐producing bacteria (Bac+) were isolated from 35 raw milk cheeses by the deferred antagonism method using Listeria strains as indicator organisms. Of the 51 Bac+ isolates, 10 that were identified as Lactococcus lactis subsp. lactis by biochemical and physiological tests, and were selected on the basis of the inhibition zone diameter (>10 mm). Five lactococcal strains containing the nisA or nisZ genes, the structural genes for nisin biosynthesis, were selected with specific PCR amplifications, and the other five isolates were shown to produce a bacteriocin different from nisin. Seven of the ten isolates including two presumptive nisogenic strains, showed good capacity for milk acidification decreasing the pH of milk from 6.5 to 4.7–4.3.
28 citations
TL;DR: Four strains of mesophilic lactic acid bacteria were separately or coentrapped in kappa-carrageenan/locust bean gum gel beads and used for continuous prefermentation of UHT skim milk in a stirred-tank bioreactor, and experimentations over seven-week periods with pasteurized milk showed the high resistance of the immobilized cellBioreactor to psychrotrophic contamination.
28 citations
TL;DR: The feasibility of using an integrated immobilized cell bioreactor for milk prefermentation in cheese manufacture is shown with results combined with published data on process performance.
Abstract: A system was developed to continuously acidify and inoculate skim milk for the production of fresh cheese. Four strains of mesophilic lactic acid bacteria were entrapped separately in kappa-carrageenan/locust bean gum gel beads and used in a stirred bioreactor operated at 26 degrees C with a 25% (v/v) gel load. The pH in the reactor was controlled at 6.0 by adding fresh milk using proportional integrated derived regulation. The bioreactor was operated during 8-h daily cycles for up to 7 weeks with different milks (heat treatment, dry matter content) and differing starting procedures. The heat treatment of the milk was an important factor for process performance: a dilution rate increase of 57% and an inoculation level decrease of 63% were observed with sterilized UHT skim milk (142 degrees C - 7.5 s) compared with pasteurized skim milk (72 degrees C - 15 s). The dry matter content of the milk (8-13% w/w) had no detectable effect on these parameters. A convenient starting procedure of the system was tested; steady-state was reached in less than 40 min following an interruption period of 16-60 h. These results combined with our published data on process performance show the feasibility of using an integrated immobilized cell bioreactor for milk prefermentation in cheese manufacture.
26 citations
TL;DR: Stability of freeze-dried cultures during storage at minus 17, 4 and 20°C was not influenced by immobilization, and survival to freeze-Drying of immobilized cells was as good as that of classical free-cell cultures.
Abstract: Bifidobacterium longum was immobilized in k-carrageenan/locust bean gum gel beads, and cultured in a medium containing Lactobacillus MRS broth and whey-permeate. The same beads were incubated for 5 successive batch fermentations and freeze-dried following mixing with a protective solution. Viable population in the beads increased from 8 3 10 7 to 4.7 3 10 10 cfu/g after three batch fermentations, but no further increase in viable cell population could be achieved in the last two fermentations. The freeze-dried culture contained 3 3 10 10 cfu/g with a survival rate of approximately 10%. Survival to freeze-drying of immobilized cells was as good as that of classical free-cell cultures. Stability of freeze-dried cultures during storage at minus 17, 4 and 20°C was not influenced by immobilization.
25 citations
TL;DR: In this paper, a study of the impact of fermentation parameters showed that pH has a significant effect on hardness, cohesion and percentage of deformation at rupture in milk (but not in the other 2 media), which may be explained by an increase in the amount of soluble calcium cations.
Abstract: Texture profile analysis and rupture tests, respectively, at a deformation of 5 and 80%, were carried out on commercial kappa-carrageenan gel cylinders (3% w/v concentration) and on mixed gel cylinders (kappa-carrageenan/iota-carrageenan or locust bean gum [LBG], in different proportions), to select the best gel composition as an immobilization matrix for continuous lactic acid fermentations of dairy media. Mixed gel cylinders were soaked in a model system for lactic fermentations consisting of 36 dairy media: milk, whey and whey permeate, with 4 lactate concentrations (5, 20, 35 and 50 g/L of medium), combined with 3 pH values (6.5, 6.0, 5.5). GENUGEL X-0909 n°5180850 was the most resistant of all commercial kappa-carrageenans available; mixing this kappa-carrageenan with LBG in the respective proportions of 2. 75 %/0.25% gave the best rheological properties to the resulting mixed gel. Our study of the impact of fermentation parameters showed that pH has a significant effect on hardness, cohesion and percentage of deformation at rupture in milk (but not in the other 2 media). A pH drop of milk from 6.5 to 5.5 resulted in more brittle gels which may be explained by an increase in the amount of soluble calcium cations. Generally, soaking in milk produced the most brittle gels due to its calcium content, whey produced the hardest gels and whey permeate, the softest. An increase in the ammonium lactate concentration significantly improved hardness, rupture force and percentage of deformation at rupture, while reducing cohesion and resilience: NH 4 + cations would account for this effect. The differences in rheological behaviour of immobilization gel beads during continuous lactic fermentations of milk and whey permeate would be due to the cation content and more specifically to the higher calcium concentration in milk.
13 citations
TL;DR: Mathematical modeling and in-situ pH measurements were used to characterize the effects of the microenvironment on alginate gel beads immobilized cells of Lactococcus lactis and the dynamics of the system is discussed in relation to the overall activity of the immobilized cell reactor.
Abstract: Mathematical modeling and in-situ pH measurements were used to characterize the effects of the microenvironment on alginate gel beads immobilized cells of Lactococcus lactis. Mass transfer limitations led to a progressive pH acidification within gel beads which determined both the cell distribution and the cellular activity of entrapped cells. The dynamics of the system is discussed in relation to the overall activity of the immobilized cell reactor.
11 citations
Patent•
08 Sep 1997TL;DR: In this paper, a simple method of purifying mutacin B-Ny266 from Streptococcus mutans strain Ny266 to homogeneity is presented, where the primary amino acid sequence and its proposed modified structure are discussed.
Abstract: Mutacin are bactericidal substances of proteinaceous natures produced by Streptococcus mutans. Lantibiotics are antibacterial substances containing posttranslationnally modified amino acids such as lanthionine. The present invention teaches a simple method of purifying mutacin B-Ny266 from Streptococcus mutans strain Ny266 to homogeneity. The present invention further teaches the primary amino acid sequence of mutacin B-Ny266 as well as its proposed modified structure. Further, the present invention teaches compositions comprising mutacin B-Ny266 as well as methods for the treatment and/or prophylaxy of bacterial infections comprising an administration of a suitable dose of composition comprising mutacin B-Ny266.