Specific effect of high-pressure treatment of milk on cheese proteolysis

The extent of primary and secondary proteolysis of cheeses made from raw (RA), pasteurized (PA, 72 degrees C, 15 s) or pressure-treated (PR, 500 MPa, 15 min, 20 degrees C) goats' milk was assessed. Modifications in cheese-making technology were introduced to obtain cheeses with the same moisture content, and thus studied per se the effect of milk treatment on cheese proteolysis.The PR milk cheese samples were differentiated from RA and PA milk cheeses by their elevated beta-lg content, and by the faster degradation of alphas1-, alphas2- and beta-CN throughout ripening. Non-significant differences were found in either pH 4.6 soluble-nitrogen or trichloracetic acid soluble-nitrogen contents of cheeses. However, the pasteurization of milk decreased the free amino acid production in cheese. The RA milk cheeses had the highest amount of proline and the lowest concentrations of serine, tyrosine, arginine and alpha-aminobutyric acid, whereas PR milk cheese showed higher levels of arginine.     

Reuterin and High Hydrostatic Pressure Treatments on the Inactivation of Listeria monocytogenes and Effect on the Characteristics of Cold-Smoked Salmon

The effect of reuterin and high hydrostatic pressure (HHP) processing at 450 MPa for 5 min on the inactivation of Listeria monocytogenes and the characteristics of cold-smoked salmon during 35 days at 4 and 10 °C were investigated. The growth rate of the pathogen was reduced by reuterin addition and a synergistic antimicrobial effect against L. monocytogenes was recorded when the biopreservative was applied in combination with HHP at 450 MPa for 5 min. This combined treatment prevented the pathogen recovery observed with individual treatments and delayed the spoilage of smoked salmon maintaining total viable counts under 3.5 log units during 35 days of storage at 4 °C. All treatments assayed induced changes in lightness (L*) and redness (a*), resulting in a brighter appearance of smoked salmon, whereas no modifications were recorded in shear strength values immediately after treatments. Moreover, reuterin and HHP treatments, individually or in combination, avoided the formation of biogenic amines during the 35 days of storage at 4 and 10 °C. The addition of reuterin in combination with HHP at 450 MPa for 5 min might be applied as a hurdle technology to improve the safety and extend the shelf life of lightly preserved seafood products, such as cold-smoked salmon.     

Evaluation of SPE as Preparative Technique for the Analysis of Phenolic Metabolites in Human Feces

Solid phase extraction (SPE) methodology has been evaluated as a cleanup strategy prior to the analysis of phenolic metabolites in fecal samples by UPLC–DAD–ESI–TQ MS. Among the sorbents tested, Oasis® HLB led to the higher phenolic standard recoveries. Sample acidification (0.4 M HCl, final concentration) before SPE considerably improved standard recoveries. Values of the process efficiency (C_SPE/C_{Without SPE}) for a standard solution containing gallic acid, protocatechuic acid, caffeic acid, benzoic acid, 3-phenylpropionic acid, (+)-catechin, (?)-epicatechin, procyanidin B2, and 4-hydroxybenzoic 2,3,5,6 d₄ acid were acceptable (>90 %) for all compounds, except for procyanidin B2 (26 %). The developed SPE methodology was applied to fecal samples of individuals subjected to a wine intervention study. Phenolic metabolites, including intermediate metabolites (phenyl-γ-valerolactones and phenylvaleric acid derivatives) and end products (simple phenols, hydroxyphenylpropionic, hydroxyphenylacetic, hydroxycinnamic, and hydroxybenzoic acids) were identified. Most of the compounds (n?=?14) exhibited values of process efficiency between 85 and 115 %. Although some compounds (n?=?4) showed process efficiency>115 %, there was a group of metabolites (4-O-methylgallic acid, syringic acid, and 4-hydroxy-5-(3′,4′-dihydroxyphenyl)-valeric acid) whose process efficiency was <85 %, which represented a serious limitation and made us to discard SPE as a preparative technique for the analysis of these phenolic metabolites. Finally, the paper reports the concentrations of phenolic metabolites in a randomized set of human fecal samples from healthy volunteers (n?=?15) without any previous SPE application. Large inter-individual variability was observed, which was attributed to differences in human gut microbiota composition.     

Determination of Phenolic Compounds in Artichoke,Garlic and Spinach by Ultra-High-Performance Liquid Chromatography Coupled to Tandem Mass Spectrometry

Phenolic compounds were determined in artichoke (Cynara scolymus), garlic (Allium sativium) and spinach (Spinacia oleracea) using a single method based on simple extraction and ultra-high-performance liquid chromatography coupled to triple quadrupole tandem mass spectrometry (UHPLC-QqQ-MS/MS). Several compounds belonging to different families, such as phenolic acids, isoflavones, flavones and flavonols, were determined. The analytical procedure was validated in all the matrices, obtaining recoveries ranging from 60 to 120 % with reproducibility values (expressed as relative standard deviations (RSDs)) lower than 26 %. Limits of quantification (LOQs) were always equal to or lower than 50 μg/kg, except to kaempferol and its glucosides in spinach (LOQs?=?75 μg/kg). Artichoke showed higher concentration of phenolic compounds (837.2 mg/kg dry weight (DW)) than garlic (26.5 mg/kg DW) or spinach (64.5 mg/kg DW). Apigenin 7-O-glucoside (from 147.0 to 722.7 mg/kg DW) was found to be the major flavonoid in all samples of artichoke investigated, while chlorogenic acid, whose concentration ranged from 37.8 to 734.7 mg/kg DW, is the major phenolic acid in this matrix. Regarding garlic, caffeic acid (from 1.7 to 28.3 mg/kg DW) and quercetin (from 9.0 to 18.9 mg/kg DW) were the compounds detected at higher concentrations, although in general the total content was very low in relation to other matrices. In relation to spinach, ferulic acid was the major phenolic compound, and its concentration ranged from 18.0 to 41.4 mg/kg DW.     

Molecular diversity of Staphylococcus aureus and the role of milking equipment adherences or biofilm as a source for bulk tank milk contamination

Staphylococcus aureus is one of the most frequent pathogens causing intramammary infections in dairy herds. Consequently, virulence factors, pathobiology, and epidemiology of Staphylococcus aureus strains have been widely assessed through the years. Nevertheless, not much has been described about the epidemiology of Staph. aureus strains from bulk tank milk (BTM) and adherences on milking equipment (AMES), even when these strains may play a role in the quality of milk that is intended for human consumption. The objective of this study was to assess the strain diversity of 166 Staph. aureus isolates collected from 3 consecutive BTM samples, and from AMES in contact with milk from 23 Chilean dairy farms. Isolates were analyzed and typed using pulsed-field gel electrophoresis. Diversity of strains, both within and among farms, was assessed using Simpson's index of diversity (SID). On farms where Staph. aureus was isolated from both AMES and BTM (n = 8), pulsotypes were further analyzed to evaluate the role of AMES as a potential source of Staph. aureus strains in BTM. Among all Staph. aureus analyzed by pulsed-field gel electrophoresis, a total of 42 pulsotypes (19 main pulsotypes and 23 subtypes) were identified. Among dairy farms, strain diversity was highly heterogeneous (SID = 0.99). Within dairy farms, Staph. aureus strain diversity was variable (SID = 0 to 1), and 18 dairy operations (81.8%) had one pulsotype that was shared between at least 2 successive BTM samples. In those farms where Staph. aureus was isolated in both AMES and BTM (n = 8), 7 (87.5%) showed a clonal distribution of Staph. aureus strains between these 2 types of samples. The overlapping of certain Staph. aureus strains among dairy farms may point out common sources of Staph. aureus among otherwise epidemiologically unrelated farms. Indistinguishable Staph. aureus strains between AMES and BTM across dairy farms suggest that Staph. aureus–containing AMES may represent a source for BTM contamination, thus affecting milk quality. Our study highlights the role of viable Staph. aureus in AMES as a source for BTM contamination on dairy farms, and also describes the overlapping and presence of specific BTM and AMES pulsotypes among farms.     

The IRC7 gene encodes cysteine desulphydrase activity and confers on yeast the ability to grow on cysteine as a nitrogen source

Although cysteine desulphydrase activity has been purified and characterized from Saccharomyces cerevisiae, the gene encoding this activity in vivo has never been defined. We show that the full‐length IRC7 gene, encoded by the YFR055W open reading frame, encodes a protein with cysteine desulphydrase activity. Irc7p purified to homogeneity is able to utilize l ‐cysteine as a substrate, producing pyruvate and hydrogen sulphide as products of the reaction. Purified Irc7p also utilized l ‐cystine and some other cysteine conjugates, but not l ‐cystathionine or l ‐methionine, as substrates. We further show that, in vivo, the IRC7 gene is both necessary and sufficient for yeast to grow on l ‐cysteine as a nitrogen source, and that overexpression of the gene results in increased H₂S production. Strains overexpressing IRC7 are also hypersensitive to a toxic analogue, S‐ethyl‐l ‐cysteine. While IRC7 has been identified as playing a critical role in converting cysteine conjugates to volatile thiols that are important in wine aroma, its biological role in yeast cells is likely to involve regulation of cysteine and redox homeostasis. Copyright © 2015 John Wiley & Sons, Ltd.     

Use of antimicrobial biodegradable packaging to control Listeria monocytogenes during storage of cooked ham

The antimicrobial effect against L. monocytogenes of biodegradable films (alginate, zein and polyvinyl alcohol) containing enterocins was investigated. Survival of the pathogen was studied by means of challenge tests performed at 6 degrees C during 8 and 29 days, for air-packed and vacuum-packed sliced cooked ham, respectively. Air packaging was tested with two concentrations of enterocins (200 and 2000 AU/cm2). Control air-packed cooked ham showed an increase of L. monocytogenes from 10(4) to 10(7) CFU/g after 8 days. By contrast, packaging with antimicrobial films effectively slowed down the pathogen's growth, leading to final counts lower than in control lots. Air-packaging with alginate films containing 2000 AU/cm2 of enterocins effectively controlled L. monocytogenes for 8 days. An increase of only 1 log unit was observed in zein and polyvinyl alcohol lots at the same enterocin concentration. Vacuum packaging with films containing enterocins (2000 AU/cm2) also delayed the growth of the pathogen. No increase from inoculated levels was observed during 15 days in antimicrobial alginate films. After 29 days of storage, the lowest counts were obtained in samples packed with zein and alginate films containing enterocins, as well as with zein control films. The most effective treatment for controlling L. monocytogenes during 6 degrees C storage was vacuum-packaging of sliced cooked ham with alginate films containing 2000 AU/cm2 of enterocins. From the results obtained it can concluded that antimicrobial packaging can improve the safety of sliced cooked ham by delaying and reducing the growth of L. monocytogenes.     

In vitro studies and preliminary in vivo evaluation of silicified concentrated collagen hydrogels

Hybrid and nanocomposite silica-collagen materials derived from concentrated collagen hydrogels were evaluated in vitro and in vivo to establish their potentialities for biological dressings. Silicification significantly improved the mechanical and thermal stability of the collagen network within the hybrid systems. Nanocomposites were found to favor the metabolic activity of immobilized human dermal fibroblasts while decreasing the hydrogel contraction. Cell adhesion experiments suggested that in vitro cell behavior was dictated by mechanical properties and surface structure of the scaffold. First-to-date in vivo implantation of bulk hydrogels in subcutaneous sites of rats was performed over the vascular inflammatory period. These materials were colonized and vascularized without inducing strong inflammatory response. These data raise reasonable hope for the future application of silica-collagen biomaterials as biological dressings.