Role of calcium in activity and stability of the Lactococcus lactis cell envelope proteinase.

The mature lactococcal cell envelope proteinase (CEP) consists of an N-terminal subtilisin-like proteinase domain and a large C-terminal extension of unknown function whose far end anchors the molecule in the cell envelope. Different types of CEP can be distinguished on the basis of specificity and amino acid sequence. Removal of weakly bound Ca2+ from the native cell-bound CEP of Lactococcus lactis SK11 (type III specificity) is coupled with a significant reversible decrease in specific activity and a dramatic reversible reduction in thermal stability, as a result of which no activity at 25 degrees C (pH 6.

Selective hydrolysis of milk proteins to facilitate the elimination of the ABBOS epitope of bovine serum albumin and other immunoreactive epitopes.

Milk proteins are hydrolyzed to prevent immunological reactions, but immunoreactive epitopes, including the ABBOS epitope of bovine serum albumin (BSA), can still be detected in commercially available milk protein hydrolysates. We used lactococcal cell-envelope proteinase (CEP) for the hydrolysis of the individual milk proteins and of mixtures thereof, or for the hydrolysis of sodium caseinate (contaminated with whey proteins). CEP exclusively degraded casein, leaving the four major whey proteins intact.

Lysis of Lactococcus lactis subsp. cremoris SK110 and its nisin-immune transconjugant in relation to flavor development in cheese.

To develop a nisin-producing cheese starter, Lactococcus lactis subsp. cremoris SK110 was conjugated with transposon Tn5276-NI, which codes for nisin immunity but not for nisin production. Cheese made with transconjugant SK110::Tn5276-NI as the starter was bitter.

Aggregation of beta-lactoglobulin and influence of D2O.

The conformational stability of beta-lactoglobulin increases in D2O over that in H2O. This is concluded from an increase in peak temperature by about 3 degrees C of differential scanning calorimetry (DSC) thermograms and from a decrease in overall aggregation rate. However, effects of pH and salt concentration on the heat-induced aggregation (reaction kinetics, DSC thermograms and aggregate growth) are similar in H2O and D2O.

Influence of charge differences in the C-terminal part of nisin on antimicrobial activity and signaling capacity.

Three mutants of the antibiotic nisin Z, in which the Val32 residue was replaced by a Glu, Lys or Trp residue, were produced and characterized for the purpose of establishing the role of charge differences in the C-terminal part of nisin on antimicrobial activity and signaling properties. 1H-NMR analyses showed that all three mutants harbor an unmodified serine residue at position 33, instead of the usual dehydroalanine. Apparently, the nature of the residue preceding the serine to be dehydrated, strongly affects the efficiency of modification.

Mechanisms of the intestinal effects of dietary fats and milk products on colon carcinogenesis.

Dietary fat may promote colon cancer by increasing fatty acids (FA) and secondary bile acids (BA) in the colonic lumen. These cytotoxic surfactants can damage colonic epithelial cells and thus induce a compensatory hyperproliferation of crypt cells. Our studies show that the hyperproliferative effect of type and amount of dietary fat is not simply due to changes in colonic FA and BA.

Skim Milk Acidification.

Skim milk was acidified slowly using glucono-delta-lactone and HCl. On lowering the pH the steric stabilization of the casein micelles diminishes and as a result the micelles exhibit attractive interactions. These interactions can be quantitatively described using an adhesive hard sphere (AHS) model.

Detection by competitive enzyme-linked immunosorbent assay of a bovine serum albumin peptide (ABBOS) in infant formulas based on hydrolyzed cow's milk protein.

Objective: Our aim was to determine whether currently available products based on hydrolyzed milk protein and a small peptide (ABBOS) in bovine serum albumin (BSA) (positions 126-144) share common antigenic sites. The commercial products are primarily developed to reduce cow's milk protein-associated allergenicity, but whether they also could be used in intervention trials to elucidate the role of BSA in the etiology of IDDM is not known.

Research Design And Methods: A sensitive competitive enzyme-linked immunosorbent assay (ELISA) using a rabbit polyclonal antibody raised against the ABBOS peptide in BSA was developed.

Reversed-phase high-performance liquid chromatographic separation of bovine kappa-casein macropeptide and characterization of isolated fractions.

From complex mixtures of non-glycosylated and differently glycosylated caseinomacropeptides (CMP; kappa-casein fragment 106-169; M(r) approximately 7000) various fractions were isolated and further purified by reversed-phase HPLC. The fractions were characterized by mass determination and composition analysis and also used in gel-permeation chromatography and NMR studies to investigate their molecular size behaviour as a function of pH, ionic strength, peptide concentration and degree of glycosylation. No evidence was found for association of any CMP fraction as a function of the experimental conditions applied, which is in contrast with suggestions made in the literature.

Consumption by Healthy Adults of Pasteurized Milk with a High Concentration of Bacillus cereus : A Double-Blind Study.

A double-blind experiment with 34 healthy human volunteers, aged between 20 and 60 years, was conducted to obtain information about the allowable concentration of B. cereus in pasteurized milk. During a period of 3 weeks the subjects were exposed to B.

Determination of denatured serum proteins in the casein fraction of heat-treated milk by capillary zone electrophoresis.

The amount of heat-denatured serum proteins in heat-treated milk could be estimated by analyzing the casein fraction, obtained by isoelectric precipitation at pH 4.6, by capillary zone electrophoresis. A hydrophilically coated capillary was used in combination with 6 M urea in a citrate buffer at pH.

The occurrence of two intracellular oligoendopeptidases in Lactococcus lactis and their significance for peptide conversion in cheese.

Two intracellular oligopeptide-preferring endopeptidases have been detected in Lactococcus lactis. A neutral thermolysin-like oligoendopeptidase (NOP) has been purified to homogeneity and an alkaline oligoendopeptidase has been partially purified. The specificity of the oligoendopeptidases towards important intermediary cheese peptides, produced by chymosin action on the caseins, clearly differs from that of the cell-envelope proteinase (CEP).

Autoregulation of nisin biosynthesis in Lactococcus lactis by signal transduction.

The post-translationally modified, antimicrobial peptide nisin is secreted by strains of Lactococcus lactis that contain the chromosomally located nisin biosynthetic gene cluster nisABTCIPRKFEG. When a 4-base pair deletion is introduced into the structural nisA gene (delta nisA), transcription of delta nisA is abolished. Transcription of the delta nisA gene is restored by adding subinhibitory amounts of nisin, nisin mutants, or nisin analogs to the culture medium, but not by the unmodified precursor peptide or by several other antimicrobial peptides.

Raising the pH of the pepsin-catalysed hydrolysis of bovine whey proteins increases the antigenicity of the hydrolysates.

Background: Hypersensitivity to cow milk protein is frequently observed in infancy. Since the pH in the infant's stomach is relatively high (pH 3-4) compared with adults (pH 2), an incomplete digestion of the milk proteins is expected to occur.

Objective: The determination of the degree of hydrolysis by pepsin of the four main proteins of bovine whey, i.

Identification of a new genetic variant of bovine beta-casein using reversed-phase high-performance liquid chromatography and mass spectrometric analysis.

Various components of the beta-casein fraction from bovine milk were separated by preparative reversed-phase high-performance liquid chromatography (RP-HPLC). They included the genetic variants beta A1, beta A2, beta A3, and an unknown component previously denoted beta X [S. Visser et al.

Characterization of plasmid-encoded citrate permease (citP) genes from Leuconostoc species reveals high sequence conservation with the Lactococcus lactis citP gene.

The citrate permease determinant (citP) in several Leuconostoc strains was demonstrated to be plasmid encoded by curing experiments and hybridization studies with a DNA fragment containing the citP gene from Lactococcus lactis subsp. lactis biovar diacetylactis NCDO176. Cloning and nucleotide sequence analysis of Leuconostoc lactis NZ6070 citP revealed almost complete identity to lactococcal citP.

Identification of Clostridium tyrobutyricum as the causative agent of late blowing in cheese by species-specific PCR amplification.

Butyric acid fermentation, the late-blowing defect in cheese, caused by the outgrowth of clostridial spores present in raw milk, can create considerable loss of product, especially in the production of semihard cheeses like Gouda cheese, but also in grana and Gruyère cheeses. To demonstrate the causative relationship between Clostridium tyrobutyricum and late blowing in cheese, many cheesemaking experiments were performed to provoke this defect by using spores from several strains of the major dairy-related clostridia. A method of PCR amplification of a part of the 16S rRNA gene in combination with hybridization with species-specific DNA probes was developed to allow the specific detection of clostridial sequences in DNAs extracted from cheeses.

Improvement of solubility and stability of the antimicrobial peptide nisin by protein engineering.

Nisin is a 3.4-kDa antimicrobial peptide that, as a result of posttranslational modifications, contains unsaturated amino acids and lanthionine residues. It is applied as a preservative in various food products.

Genetic marking of Lactococcus lactis shows its survival in the human gastrointestinal tract.

A human feeding study was performed with Lactococcus lactis TC165.5, which is genetically marked by insertion of the sucrose-nisin conjugative transposon Tn5276 and chromosomal resistance to rifampin and streptomycin. The fate of strain TC165.

Identification and characterization of the insertion element IS1070 from Leuconostoc lactis NZ6009.

A novel insertion sequence, designated IS1070, was identified on the lactose plasmid of Leuconostoc lactis NZ6009 by nucleotide sequence analysis. The 1027-bp sequence contains partially matched (24 of 28 bp) inverted repeats and has one long open reading frame. The deduced 305-amino-acid sequence demonstrated homology to transposases of IS30 from Escherichia coli, IS4351 from Bacteroides fragilis, IS1086 from Alcaligenes eutrophus, IS1161 from Streptococcus salivarius, ISAS2 from Aeromonas salmonicida and a putative protein encoded by ORF3 of virus SpV1-R8A2 B from Spiroplasma citri.

A model for the denaturation and aggregation of beta-lactoglobulin.

A quantitatively correct kinetic model for the temperature-induced denaturation and aggregation of beta-lactoglobulin is presented. The model recognizes an initiation, a propagation and a termination step by analogy with polymer radical chemistry. The decrease in native beta-lactoglobulin is predicted to follow order 3/2, in agreement with experimental results.

Action of a cell-envelope proteinase (CEPIII-type) from Lactococcus lactis subsp. cremoris AM1 on bovine kappa-casein.

The specificity of the cell-envelope proteinase (CEPIII-type) from Lactococcus lactis subsp. cremoris AM1 in its action on bovine kappa-casein was studied. A 4-h digest (pH 6.

Molecular Mass Distribution Immunological Properties Nutritive Value of Whey Protein Hydrolysates.

Whey protein concentrate was hydrolyzed using the technical food-grade enzyme Corolase 7092 in order to abolish the allergenicity of whey proteins. The immunological properties of the hydrolysates were tested with a human-immunoglobulin E (human-IgE) enzyme-linked immunosorbent assay (ELISA) using sera obtained from children allergic to milk proteins and with a mouse-rat heterologous passive cutaneous anaphylactic test and an anaphylactic shock test in mice. The protein efficiency ratio, determined in young growing rats, was compared to that of casein.

Distribution and evolution of nisin-sucrose elements in Lactococcus lactis.

The distribution, architecture, and conjugal capacity of nisin-sucrose elements in wild-type Lactococcus lactis strains were studied. Element architecture was analyzed with the aid of hybridizations to different probes derived from the nisin-sucrose transposon Tn5276 of L. lactis NIZO R5, including its left and right ends, the nisA gene, and IS1068 (previously designated iso-IS904), located between the left end and the nisA gene.

Characterization of the adsorption of conjugated and unconjugated bile acids to insoluble, amorphous calcium phosphate.

Recently we showed that supplemental dietary calcium stimulates the intestinal formation of insoluble calcium phosphate and decreases the ratio of dihydroxy to trihydroxy bile acids in human duodenal bile. Because previous in vitro studies indicated that these effects could be due to differential adsorption of bile acids to amorphous calcium phosphate, we characterized the binding of bile acids to calcium phosphate. Freshly formed, amorphous, calcium phosphate bound and thus precipitated glycine-conjugated and unconjugated bile acids, whereas taurine-conjugated bile acids showed little binding.