Staphylococcus aureus virulence and metabolism are dramatically affected by Lactococcus lactis in cheese matrix.

In complex environments such as cheeses, the lack of relevant information on the physiology and virulence expression of pathogenic bacteria and the impact of endogenous microbiota has hindered progress in risk assessment and control. Here, we investigated the behaviour of Staphylococcus aureus, a major foodborne pathogen, in a cheese matrix, either alone or in the presence of Lactococcus lactis, as a dominant species of cheese ecosystems. The dynamics of S.

The production of intrinsically labeled milk protein provides a functional tool for human nutrition research.

Oral or intravenous administration of labeled, free amino acids does not allow the direct assessment of protein digestion and absorption kinetics following dietary protein intake. Consequently, dietary protein sources with labeled amino acids incorporated within the protein are required. The aim of this study was to produce milk proteins intrinsically labeled with l-[1-(13)C]phenylalanine that would allow the assessment of protein digestion and absorption kinetics and the subsequent muscle protein synthetic response to dietary protein intake in vivo in humans.

Ingestion of a protein hydrolysate is accompanied by an accelerated in vivo digestion and absorption rate when compared with its intact protein.

Background: It has been suggested that a protein hydrolysate, as opposed to its intact protein, is more easily digested and absorbed from the gut, which results in greater plasma amino acid availability and a greater muscle protein synthetic response.

Objective: We aimed to compare dietary protein digestion and absorption kinetics and the subsequent muscle protein synthetic response to the ingestion of a single bolus of protein hydrolysate compared with its intact protein in vivo in humans.

Design: Ten elderly men (mean +/- SEM age: 64 +/- 1 y) were randomly assigned to a crossover experiment that involved 2 treatments in which the subjects consumed a 35-g bolus of specifically produced L-[1-(13)C]phenylalanine-labeled intact casein (CAS) or hydrolyzed casein (CASH).

Tina wooden vat biofilm: a safe and highly efficient lactic acid bacteria delivering system in PDO Ragusano cheese making.

In the Sicilian PDO Ragusano cheese making, raw milk is placed in a wooden vat called a Tina. As no starter is added, lactic acid is produced by milk flora and flora released from the Tina biofilm. The aim of this work was to assess the safety and efficiency of this natural inoculation system.

Ultra high temperature treatment, but not pasteurization, affects the postprandial kinetics of milk proteins in humans.

Although the chemical and physical modifications to milk proteins induced by technological treatments have been characterized extensively, their nutritional consequences have rarely been assessed in humans. We measured the effect of 2 technological treatments on the postprandial utilization of milk nitrogen (N), pasteurization (PAST) and ultra high temperature (UHT), compared with microfiltration (MF), using a sensitive method based on the use of milk proteins intrinsically labeled with (15)N. Twenty-five subjects were studied after a 1-wk standardization of their diet.

RNA extraction from cheese for analysis of in situ gene expression of Lactococcus lactis.

Aims: The isolation of high-quality RNA from cheese is a prerequisite for analysis of in situ gene expression of dairy micro-organisms.

Methods And Results: A method for rapid isolation of bacterial cells from cheese using cold citrate buffer followed by mechanical cell disruption was developed. RNA was extracted from experimental ultrafiltration (UF) cheeses (at 2, 8, 24 h, 7 and 14 days) and from Cheddar cheese (from 1 day to 1 year).

Compared with casein or total milk protein, digestion of milk soluble proteins is too rapid to sustain the anabolic postprandial amino acid requirement.

Background: The in vivo quality of milk protein fractions has seldom been studied in humans.

Objective: Our objective was to compare the postprandial utilization of dietary nitrogen from 3 [(15)N]-labeled milk products: micellar caseins (MC), milk soluble protein isolate (MSPI), and total milk protein (TMP).

Design: The macronutrient intakes of 23 healthy volunteers were standardized for 1 wk, after which time the subjects ingested a meal containing MC (n = 8), MSPI (n = 7), or TMP (n = 8).

Microfiltration of raw whole milk to select fractions with different fat globule size distributions: process optimization and analysis.

We present an extensive description and analysis of a microfiltration process patented in our laboratory to separate different fractions of the initial milk fat globule population according to the size of the native milk fat globules (MFG). We used nominal membrane pore sizes of 2 to 12 microm and a specially designed pilot rig. Using this process with whole milk [whose MFG have a volume mean diameter (d43) = 4.

Heat markers and quality indexes of industrially heat-treated [15N] milk protein measured in rats.

To determine the bioavailability of industrially heat-treated milk proteins, male Wistar rats were given [15N]-labeled meals containing either nonheated-micellar casein (CAS), milk soluble protein isolate (MSPI), and microfiltered milk (MF)-or heated products-"high temperature short time" pasteurized (HTST), "higher temperature, shorter time" pasteurized (HHST), ultrahigh temperature-treated (UHT), and spray-dried (SPRAY) milks. The postprandial distribution of dietary nitrogen was measured in the splanchnic area and urea. Digestibility was around 96% except for SPRAY (94%) and MSPI (98%).

The rate of protein digestion affects protein gain differently during aging in humans.

In young men ingesting protein meals, slowly digested proteins (caseins: CAS) induce a higher protein gain than those that are rapidly digested (whey proteins: WP). Our aim was to assess whether or not this is true in elderly men receiving mixed meals. The effects of meals containing either CAS or two different amounts of WP (WP-iN: isonitrogenous with CAS, or WP-iL: providing the same amount of leucine as CAS) on protein metabolism (assessed by combining oral and intravenous leucine tracers) were compared in nine healthy, elderly (mean +/- S.

Heat-induced covalent complex between casein micelles and beta-lactoglobulin from goat's milk: identification of an involved disulfide bond.

Goat milk is characterized by a very low heat stability that could be attributed, in part, to the covalent interaction between whey proteins and casein micelles. However, the formation of such a complex in goat milk has never been evidenced. This study was designed to assess whether heat-induced covalent interaction occurs between purified casein micelles and beta-lactoglobulin.

Advances in cooled semen technology.

In the horse industry, milk or milk-based extenders are used routinely for dilution and storage of semen cooled to 4-8 degrees C. Although artificial insemination (AI) with chilled and transported semen has been in use for several years, pregnancy rates are still low and variable related to variable semen quality of stallions. Over the years, a variety of extenders have been proposed for cooling, storage and transport of stallion semen.

Goats' milk of defective alpha(s1)-casein genotype decreases intestinal and systemic sensitization to beta-lactoglobulin in guinea pigs.

Contradictory results have been reported on the use of goats' milk in cows' milk allergy. In this study the hypothesis was tested, using a guinea pig model of cows' milk allergy, that these discrepancies could be due to the high genetic polymorphism of goats' milk proteins. Forty guinea pigs were fed over a 20 d period with pelleted diets containing one of the following: soyabean proteins (group S), cows' milk proteins (group CM), goats' milk proteins with high (group GM1) or low (group GM2) alpha(s1)-casein content.

The digestion rate of protein is an independent regulating factor of postprandial protein retention.

To evaluate the importance of protein digestion rate on protein deposition, we characterized leucine kinetics after ingestion of "protein" meals of identical amino acid composition and nitrogen contents but of different digestion rates. Four groups of five or six young men received an L-[1-13C]leucine infusion and one of the following 30-g protein meals: a single meal of slowly digested casein (CAS), a single meal of free amino acid mimicking casein composition (AA), a single meal of rapidly digested whey proteins (WP), or repeated meals of whey proteins (RPT-WP) mimicking slow digestion rate. Comparisons were made between "fast" (AA, WP) and "slow" (CAS, RPT-WP) meals of identical amino acid composition (AA vs.

New genetic variants identified in donkey's milk whey proteins.

Novel genetic variants for donkey milk lysozyme and beta-lactoglobulins I and II have been identified by the combined use of peptide mass mapping and sequencing by tandem mass spectrometry in association with database searching. The novel donkey lysozyme variant designated as lysozyme B (Mr 14,631 Da) differed in three amino acid exchanges, N49 --> D, Y52 --> S, and S61 --> N, from the previously published sequence. Three novel genetic variants for donkey beta-lactoglobulins were identified.

Characterization by ionization mass spectrometry of lactosyl beta-lactoglobulin conjugates formed during heat treatment of milk and whey and identification of one lactose-binding site.

The extent of the early stage of the Maillard-type reaction that impaired functional properties of whey proteins was evaluated by electrospray ionization mass spectrometry. Under conditions of mild heat treatment (63 degrees C for 20 s) applied to milk before whey separation at room temperature 23 degrees C), a modification of the relative molecular mass of beta-lactoglobulin (beta-LG) was observed that differed from that of the native form by 324. This specific modification of beta-LG occurred in acidified whey as well as in sweet whey and increased with the extent of the heat treatment.

Effect of milk fractions on survival of equine spermatozoa.

Milk-based semen diluents are known to be practical and effective in protecting equine spermatozoa during storage. Due to complex composition of milk, the components which are beneficial or harmful to spermatozoa are unknown. To address these unknowns the effect of various milk fractions on motility of stallion spermatozoa was evaluated.

Acute postprandial changes in leucine metabolism as assessed with an intrinsically labeled milk protein.

Mechanisms of protein gain during protein feeding have been investigated using a combination of oral and intravenous labeled leucine in healthy young men. The oral labeled leucine was administered as a free oral tracer ([13C]- or [2H3]leucine) added to unlabeled whey protein or as whey protein intrinsically labeled with L-[1-13C]leucine. When the oral tracer was free leucine, it appeared in the plasma more rapidly than the unlabeled leucine derived from the whey protein, and this resulted in an artifactual 88% decrease of protein breakdown.

Production of large amounts of [13C]leucine-enriched milk proteins by lactating cows.

During protein metabolism kinetic studies, oral tracers are administered as labeled free amino acids and do not necessarily represent the metabolic fate of amino acids ingested as proteins. However, sufficient quantities of 13C-labeled proteins are not currently available. We here present a new methodology for producing large amounts of milk proteins intrinsically labeled with [13C]leucine.