Identification of new antimicrobial peptides that contribute to the bactericidal activity of egg white against Salmonella enterica serovar Enteritidis at 45 °C

A recent work revealed that egg white (EW) at 45 °C exhibits powerful bactericidal activity against S. enterica serovar Enteritidis, which is surprisingly little affected by removal of the >10 kDa EW proteins. Here, we sought to identify the major EW factors responsible for this bactericidal activity by fractionating EW using ultrafiltration and nanofiltration and by characterizing the physicochemical and antimicrobial properties of the resulting fractions. In particular, 22 peptides were identified by nano-LC/MSMS and the bactericidal activities of representative peptides (with predicted antimicrobial activity) were further assessed. Two peptides (FVPPVQR and GDPSAWSWGAEAHS) were found to be bactericidal against S. enterica serovar Enteritidis at 45 °C when provided in an EW environment. Nevertheless, these peptides contribute only part of this bactericidal activity, suggesting other, yet to be determined, antimicrobial factors

A Temporal -omic Study of Propionibacterium freudenreichii CIRM-BIA1T Adaptation Strategies in Conditions Mimicking Cheese Ripening in the Cold

Propionibacterium freudenreichii is used as a ripening culture in Swiss cheese manufacture. It grows when cheeses are ripened in a warm room (about 24°C). Cheeses with an acceptable eye formation level are transferred to a cold room (about 4°C), inducing a marked slowdown of propionic fermentation, but P. freudenreichii remains active in the cold. To investigate the P. freudenreichii strategies of adaptation and survival in the cold, we performed the first global gene expression profile for this species. The time-course transcriptomic response of P. freudenreichii CIRM-BIA1T strain was analyzed at five times of incubation, during growth at 30°C then for 9 days at 4°C, under conditions preventing nutrient starvation. Gene expression was also confirmed by RT-qPCR for 28 genes. In addition, proteomic experiments were carried out and the main metabolites were quantified. Microarray analysis revealed that 565 genes (25% of the protein-coding sequences of P. freudenreichii genome) were differentially expressed during transition from 30°C to 4°C (P<0.05 and |fold change|>1). At 4°C, a general slowing down was observed for genes implicated in the cell machinery. On the contrary, P. freudenreichii CIRM-BIA1T strain over-expressed genes involved in lactate, alanine and serine conversion to pyruvate, in gluconeogenesis, and in glycogen synthesis. Interestingly, the expression of different genes involved in the formation of important cheese flavor compounds, remained unchanged at 4°C. This could explain the contribution of P. freudenreichii to cheese ripening even in the cold. In conclusion, P. freudenreichii remains metabolically active at 4°C and induces pathways to maintain its long-term survival

Fatty acid composition of total fat from Camembert cheeses with small and large native milk fat globules

Camembert cheeses were produced using either small (∼3 pm, SFG) or large (∼6 μm, LFG) native milk fat globules obtained by a patented microfiltration process. The total fatty acid composition in cheeses varied both according to ripening time and fat globule size. There were more medium-chain fatty acids in SFG cheeses, the content of which decreased with ripening time. Twenty days after manufacture, there were more saturated and unsaturated C18 acids in LFG than in SFG, on average. There was considerably more short-chain fatty acids in SFG than LFG at 40 days after manufacture, which can develop aromas. Sensory analysis revealed that the flavour intensity and richness of aromas were greater in SFG cheese. Results were explained by the greater surface area of native milk fat globule membrane for SFG vs LFG, at a given fat content, which can enhance lipolytic activity. The use of native milk fat globules with different sizes can thus lead to products with different sensory properties

CLA profile in native fat globules of different sizes selected from raw milk

The CLA content and isomer profile were characterized among two subclasses of the native milk fat globules. The latter corresponded to two fractions obtained by a microfiltration process using Spring mixed milk, leading to small fat globules (SFG; Click to view the MathML source) in the microfiltrates and large ones (LFG; Click to view the MathML source) in the retentates. Relatively, SFG always contained more CLA than the LFG originating from the same mixed milk, though discrepancies among different milk samples were observed. The main CLA isomer was the cis-9, trans-11, the content of which tended to increase when the native milk fat globule size decreased (from 82.2% to 87.3% of total CLA isomers). Consequently, the SFG contained less trans-12, trans-14; trans-11, trans-13; trans-11, cis-13 and trans-8, cis-10 isomers than the corresponding LFG. However, the relative variation of some isomers between small and large fat globule from the same milk varied depending on milk origin and the potential of fat globule fractionation for influencing the content and distribution of CLA seems to be limited

Emmental cheese environment enhances Propionibacterium freudenreichii stress tolerance

Dairy propionibacteria are actinomycetales found in various fermented food products. The main species, Propionibacterium freudenreichii , is generally recognized as safe and used both as probiotic and as cheese starter. Its probiotic efficacy tightly depends on its tolerance towards digestive stresses, which can be largely modulated by the ingested delivery vehicle.Indeed, tolerance of this bacterium is enhanced when it is consumed within a fermented dairy product, compared to a dried probiotic preparation. We investigated both stress toler- ance and protein neosynthesis upon growth in i) chemically defined or ii) aqueous phase of Emmental cheeses. Although the same final population level was reached in both media, a slower growth and an enhanced survival of CIRM BIA 1 strain of P. freudenreichii subsp. shermanii was observed in Emmental juice, compared to chemically defined medium. This was accompanied by differences in substrates used and products released as well as over- expression of various early stress adaptation proteins in Emmental juice, compared to chem-ically defined medium, implied in protein folding, in aspartate catabolism, in biosynthesis ofvaline, leucine and isoleucine, in pyruvate metabolism in citrate cycle, in the propionate metabolism, as well as in oxidoreductases. All these changes led to a higher digestive stress tolerance after growth in Emmental juice. Mechanisms of stress adaptation were induced in this environment, in accordance with enhanced survival. This opens perspectives for the use of hard and semi-hard cheeses as delivery vehicle for probiotics with enhanced efficac

Plateau analytique de spectrométrie de masse de l'UMR STLO : Pour de meilleurs aliments

Depuis sa création, l’UMR Science et Technologie du Lait et de l’OEuf(Rennes), mobilise ses ressources au service de la qualité, de lafonctionnalité et de la sécurité de l’aliment.Aujourd’hui, la dimension nutritionnelle est intensifiée via l’exploration dela déstructuration de l’aliment dans le tractus intestinal

Multiscale characterization of the organization of triglycerides and phospholipids in Emmental cheese: From the microscopic to the molecular level

Multiscale characterization of the organization of triglycerides and phospholipids in Emmental cheese: From the microscopic to the molecular leve

Plateau analytique de spectrométrie de masse de l'UMR STLO : Pour de meilleurs aliments

Depuis sa création, l’UMR Science et Technologie du Lait et de l’OEuf(Rennes), mobilise ses ressources au service de la qualité, de lafonctionnalité et de la sécurité de l’aliment.Aujourd’hui, la dimension nutritionnelle est intensifiée via l’exploration dela déstructuration de l’aliment dans le tractus intestinal

Differently sized native milk fat globules separated by microfilftration: fatty acid composition of the milk fat globule membrane and triglyceride core

The aim of this study was to characterize the fatty acid composition of the core and membrane of differently sized milk fat globules separated by microfiltration, which can now be used to manufacture dairy products. Native milk fat globules of various mean diameters, ranging from d43 = 2.3 µm to 8.0 µm, were obtained using microfiltration of raw whole milk. After milk fat globule washing, the milk fat globule membrane (MFGM) and the triglyceride core (TC) were separated by manual churning. After total lipid extraction from each fraction, their fatty acid composition was characterized using methyl ester analysis by gas chromatography. Regardless of season, no significant differences were observed in the fatty acid composition of the MFGM phospholipids. Conversely, significant differences were found in the fatty acid composition of TC; particularly, small fat globule TC contained more medium-chain fatty acids and less stearic acid than large fat globule TC. These results show that the previously observed differences in total fatty acid composition among differently sized milk fat globules are due to their triglyceride composition and MFGM amount rather than to the composition of the MFGM

The dispersion state of milk fat influences triglyceride metablism in the rat A13CO2 breath test study

Background Milk fat, which has different structures in the various dairy products, is a major and controversial lipid source in the Western diet. However, information about the digestion fate of milk fat depending on its supramolecular structure for a given composition is scarce. Aim of the study In this study, 13CO2 breath tests were performed with fasted rats force–fed different dairy preparations of similar composition but differing in fat suprastructure in order to highlight differences of general lipid metabolism. Methods Each preparation consisted of a NaCl solution, anhydrous milk fat labelled with a 13C mixed triacylglycerol, casein (as native phosphocaseinate powder with some lactose), and dipalmitoylphosphatidylcholine. Milk fat was either fed (i) unemulsified consecutively to the aqueous phase, or emulsified as (ii) coarse droplets of ∼10 µm covered mainly with the phospholipid, or (iii–iv) fine droplets of ∼1 µm covered mainly with casein, force–fed either in the liquid state or in a semi–crystallized state. 13C abundance in expired air samples was measured by isotope ratio mass spectrometry; results were expressed as 13C enrichment and were submitted to an ANOVA analysis. Results The 13CO2 excretion curves of the unemulsified preparation and the coarse emulsion were similar and presented a sharp peak, both significantly different from the fine emulsion curves characterized by a nearly linear cumulative recovery. The crystalline state of the fine emulsion droplets and the viscosity of these emulsions did not affect significantly their excretion curves. The lipid metabolization (indicated by the 13C recovery) was significantly slower for the fine droplets coated with casein than for the large droplets coated with the phospholipid and the unemulsified fat. For the latter, a single 13C peak rapidly appeared, while for small droplets coated with caseins, 13C excretion was continuous up to 6 h. Conclusions Global lipid metabolism based on oxidation to CO2 was decreased with smaller compared to larger emulsified milk fat particles with different coatings. These data support the concept that dairy products with different fat suprastructures are digested and metabolized differently