Variability in true protein, casein, nonprotein nitrogen, and proteolysis in high and low somatic cell milks

Does the age of milk affect its mid-infrared spectrum and predictions?

Milk of dairy species commonly undergo standardized official analyses, these that may require chemical preservation and transportation to a certified laboratory. In this context, storage duration is an important factor that can potential affect both milk chemical analyses and its mid-infrared spectrum. We analysed milk samples at different time points/ages to assess repeatability and reproducibility of mid-infrared predicted traits (e.g., fat and protein). Using spectral data, we also evaluated the ability of spectroscopy coupled with chemometrics to discriminate samples according to their age. Although the main components of milk remained consistently reproducible across age (days), changes in the spectrum due to sample aging and deterioration of the matrix were detectable. Using a discriminant analysis, we achieved a classification accuracy of 77% in validation. Predicting milk age using mid-infrared spectra is feasible, allowing for sample monitoring within circuits where maximum reliability is needed, e.g., bulk or individual milk samples for legal/official use or payment systems.

Effect of dipotassium phosphate addition and heat on proteins and minerals in milk protein beverages

Our objective was to determine the effects of dipotassium phosphate (DKP) addition, heat treatments (no heat, high temperature, short time [HTST]: 72°C for 15 s, and direct steam injection UHT: 142°C for 2.3 s), and storage time on the soluble protein composition and mineral (P, Ca, K) concentration of the aqueous phase around casein micelles in 7.5% milk protein-based beverages made with liquid skim milk protein concentrate (MPC) and micellar casein concentrate (MCC). Milk protein concentrate was produced using a spiral wound polymeric membrane, and MCC was produced using a 0.1-µm ceramic membrane by filtration at 50°C. Two DKP concentrations were used (0% and 0.15% wt/wt) within each of the 3 heat treatments. All beverages had no other additives and ran through heat treatment without coagulation. Ultracentrifugation (2-h run at 4°C) supernatants of the beverages were collected at 1, 5, 8, 12, and 15-d storage at 4°C. Phosphorus, Ca, and K concentrations in the beverages and supernatants were measured using inductively coupled plasma spectrometry. Protein composition of supernatants was measured using Kjeldahl and sodium dodecyl sulfate-PAGE. Micellar casein concentrate and MPC beverages with 0.15% DKP had higher concentrations of supernatant protein, Ca, and P than beverages without DKP. Protein, Ca, and P concentrations were higher in MCC supernatant than in MPC supernatant when DKP was added, and these concentrations increased over storage time, especially when lower heat treatments (HTST or no heat treatment) had been applied. Dipotassium phosphate addition caused the dissociation of αS-, β-, and κ-casein, and casein proteolysis products out of the casein micelles, and DKP addition explained over 70% of the increase in supernatant protein, P, and Ca concentrations. Dipotassium phosphate could be removed from 7.5% of protein beverages made with fresh liquid MCC and MPC (containing a residual lactose concentration of 0.6% to 0.7% and the proportional amount of soluble milk minerals), as these beverages maintain heat-processing stability without DKP addition.

Effect of temperature and protein concentration on the protein types within the ultracentrifugation supernatant of liquid micellar casein concentrate

Liquid micellar casein concentrate (MCC) is an ideal milk-based protein ingredient for neutral-pH ready-to-drink beverages. The texture and mouthfeel of liquid MCC-based beverages depend on the beverage protein content, as well as the composition of soluble proteins in the aqueous phase around the casein micelle. The objective of this study was to determine the composition of soluble proteins in the aqueous phase around the casein micelles in skim milk and liquid MCC containing 7.0% and 11.6% protein content. Skim milk was pasteurized and concentrated to 7% protein content by microfiltration and then to 18% protein content by ultrafiltration. The 18% MCC was then serially diluted with distilled water to produce 11.6% and 7.0% protein MCC. Skim milk, 7.0% MCC, and 11.6% MCC representing starting materials with different protein concentrations were each ultracentrifuged at 100,605 × g for 2 h. The ultracentrifugation for each of the starting materials was performed at 3 different temperatures: 4°C, 20°C, and 37°C. The ultracentrifugation supernatants were collected to represent the aqueous phase around the casein micelle in MCC solutions. The supernatants were analyzed by Kjeldahl to determine the crude protein, casein, and casein as a percentage of crude protein content, and by sodium dodecyl sulfate PAGE to determine the composition of the individual proteins. Most of the proteins in MCC supernatant (about 45%) were casein proteolysis products. The remaining proteins in the MCC supernatant consisted of a combination of intact αS-, β-, and κ-caseins (about 40%) and serum proteins (14-18%). Concentrations of αS-casein and β-casein in the supernatant increased with decreasing temperature, especially at higher protein concentrations. Temperature and interaction between temperature and protein explained about 80% of the variation in concentration of supernatant αS- and β-caseins. Concentration of supernatant κ-casein, casein proteolysis products, and serum protein increased with increasing MCC protein concentration, and MCC protein concentration explained most of the variation in supernatant κ-casein, casein proteolysis products, and serum protein concentrations. Predicted MCC apparent viscosity was positively associated with the dissociation of αS- and β-caseins. Optimal beverage viscosity could be achieved by controlling the dissociation of these proteins in MCC.

An integrated approach to the analysis of antioxidative peptides derived from Gouda cheese with a modified β-casein content

This study is the first to present an integrated approach involving in silico and in vitro protocols that was pursued to analyse an antioxidative potency of Gouda cheese with modified content of β-casein. Firstly, the predictions of the presence of antioxidant peptides in the casein sequences were computed using the BIOPEP-UWM database. Then, the antioxidative bioactivity of six variants of Gouda cheese (with reduced, normative, and increased content of β-casein at the initial and final stage of ripening) was assessed. Finally, the RP-HPLC–MS/MS was applied to identify antioxidative peptides in Gouda-derived water-soluble extracts (WSEs). Analyses were supported with the heatmaps and the computation of parameters describing the efficiency of proteolysis of caseins in the modified Gouda cheeses, i.e., the frequency and the relative frequency of the release of antioxidative fragments during cheese ripening (A_Eexp and W_exp., respectively). All Gouda cheese variants exhibited the antioxidative potential which differed depending on the assay employed. The highest antioxidative activity (ABTS^·+ radical scavenging effect, FRAP, and Fe-chelating) was observed for WSEs derived from Gouda cheese with increased content of β-casein after the 60th day of ripening. The results obtained suggest the potential of Gouda cheese as the antioxidant-promoting food.

Protein Preparations as Ingredients for the Enrichment of Non-Fermented Milks

Milk enriched with functional ingredients of milk proteins delivers health and nutritional benefits, and it can be particularly recommended to consumers with increased protein requirements. The aim of this study was to evaluate the applicability of casein and serum protein preparations obtained by membrane filtration in the laboratory as additives to non-fermented milks, as compared with commercial protein, preparations (whey protein isolate or concentrate and casein concentrate). The addition of protein preparations increased the pH, viscosity and heat stability of non-fermented milks. Milks enriched with whey proteins were characterized by a higher content of valine and isoleucine and a lower content of leucine, lysine and arginine. Addition of casein or whey protein concentrate decreased the phosphorus content and increased the calcium content of milk, but only in the products enriched with casein or whey protein concentrate. Color saturation was higher in products fortified with protein preparations obtained in the laboratory and commercial whey protein concentrate. Milk enriched with whey protein isolate, followed by milk serum protein concentrate, received the highest scores in the sensory evaluation. The presented results make a valuable contribution to the production of milks enriched with various protein fractions. The study proposes the possibility of production of protein preparations and milks enhanced with protein preparations, which can be implemented in industrial dairy plants.

Effects of micellar casein concentrate purity and milk fat on sulfur/eggy flavor in ultrapasteurized milk-based beverages

Our objectives were to determine the level of milk-derived whey protein (MDWP) removal necessary to achieve no detectable sulfur/eggy flavor in ultrapasteurized fat-free micellar casein concentrate (MCC) beverages (6.5% protein) and in the same beverages containing 1 and 2% milk fat. Micellar casein concentrate with 95% MDWP removal was produced from skim milk (50°C) with a 3×, 3-stage ceramic microfiltration (MF) process using 0.1-µm pore size graded permeability membranes (n = 3). In experiment 1, MCC-based beverages at about 6.5% (wt/wt) true protein were formulated at a fat content of 0.15% fat (wt/wt) at 4 different levels of MDWP removal percentages (95.2%, 91.0%, 83.2%, and 69.3%). In experiment 2, a similar series of beverages at 3 MDWP removal percentages (95.2%, 83.2%, and 69.3%) with 0.1, 1, and 2% fat content were produced. The purity (or completeness of removal of whey protein by MF) of MCC was determined by the Kjeldahl method and sodium dodecyl sulfate (SDS)-PAGE. Sensory properties of beverages were documented by descriptive sensory analysis, and volatile sulfur compounds were evaluated using solid-phase microextraction followed by gas chromatography-triple quadrupole mass spectrometry. The purity of MCC measured by the Kjeldahl method (casein as a percentage of true protein) was higher after thermal treatment than before, whereas MCC purity evaluated by SDS-PAGE was unchanged by heat treatment. The purity of MCC had an effect on the flavor profile of thermally processed beverages at 6.5% protein made with fresh liquid MCC. No sulfur/eggy flavor was detected in MCC beverages when 95% of the MDWP was removed (MCC purity about 93 to 94%) from skim milk by microfiltration at 0.1, 1, and 2% fat. As the fat content of 6.5% protein beverages produced with MCC increased, sulfur/eggy flavor intensity and hydrogen sulfide concentration decreased. However, the effect of increasing milk fat on reducing sulfur/eggy flavor in MCC-based beverages at 6.5% protein was less than that of increasing MDWP removal from MCC. Sulfur off-flavors in neutral-pH dairy protein beverages can be mitigated by use of high-purity MCC or by incorporation of fat in the beverage, or both.

The Effect of High-Pressure Treatment and Skimming on Caprine Milk Proteins

Background: Proteins are susceptible to HP-treatment and there is a need to determine the applicability of HP-treatment in dairy production. The aim of this study was to determine the effect of HP-treatment at 200–500 MPa (tconst. = 10 min; Tconst. = 20 °C) and skimming of HP-treated milk on the content of nitrogen compounds and protein composition of caprine milk. Methods: The content of nitrogen (total, non-casein, non-protein) was determined using the Kjeldahl method. Casein fractions and whey proteins were separated using SDS-PAGE electrophoresis. Color parameters were measured in the CIELAB color space. Results: HP-treatment decreased (p < 0.05) the content of non-casein nitrogen and soluble whey proteins. Skimming decreased the content of nitrogen compounds, and the noted decrease was more pronounced in HP-treated milk. Pressure and skimming had no influence on the proportions of α-, β-, κ-casein, β-lactoglobulin and α-lactalbumin. Total color difference (ΔE) increased with a rise in pressure, particularly in skim milk. Conclusion: HP-treatment led to a loss of protein solubility at pH 4.6 in caprine milk. In HP-treated milk, skimming did not induce changes in protein composition, despite a decrease in the content of nitrogen compounds after the separation of the cream layer. Higher values of ΔE in skim milk than in whole milk point to changes in colloidal phase components.

Transmission of Major and Minor Serum Proteins during Microfiltration of Skim Milk: Effects of Pore Diameters, Concentration Factors and Processing Stages

Effects of pore diameters (100, 50, and 20 nm), concentration factors (1-8) and processing stages (1-5) on the transmission of major serum proteins (β-lactoglobulin and α-lactalbumin) and minor serum proteins (immunoglobulin (Ig) G, IgA, IgM, lactoferrin (LF), lactoperoxidase (LPO), xanthine oxidase (XO)) during ceramic microfiltration (MF) of skim milk were studied. Holstein skim milk was microfiltered at a temperature of 50 °C, a transmembrane pressure of 110 kPa and a crossflow velocity of 6.7 m/s, using a tubular single stainless steel module that consisted of three ceramic tubes, each with 19 channels (3.5 mm inner diameter) and a length of 0.5 m. For MF with 100 nm and 50 nm pore diameters, the recovery yield of major serum proteins in permeate was 44.3% and 44.1%, while the recovery yield of minor serum proteins was slightly less by 0%-8% than 50 nm MF. MF with 20 nm pore diameters showed a markedly lower (by 12%-45%) recovery yield for both major and minor serum proteins, corresponding with its lower membrane flux. Flux sharply decreased with an increasing concentration factor (CF) up to four, and thereafter remained almost unchanged. Compared to the decrease (88%) of flux, the transmission of major and minor serum proteins was decreased by 4%-15% from CF = one to CF = eight. With increasing processing stages, the flux gradually increased, and the recovery yield of both major and minor proteins in the permeate gradually decreased and reached a considerably low value at stage five. After four stages of MF with 100 nm pore diameter and a CF of four for each stage, the cumulative recovery yield of major serum proteins, IgG, IgA, IgM, LF, LPO, and XO reached 95.7%, 90.8%, 68.5%, 34.1%, 15.3%, 39.1% and 81.2% respectively.

Measurement of casein in milk by Kjeldahl and sodium dodecyl sulfate-polyacrylamide gel electrophoresis

Our objectives were to determine if milk casein as a percentage of true protein (CN%TP) estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) is equivalent to CN%TP estimated by Kjeldahl, and to determine the proportion of casein (CN), casein proteolysis products (CNPP), and serum protein (SP) from milk true protein (TP) that goes into the Kjeldahl noncasein nitrogen (NCN) filtrate and the proportion that stays in the NCN precipitate using SDS-PAGE. Raw milk samples were collected from 16 mid-lactation Holstein cows twice a week for 2 wk. These milks were analyzed for Kjeldahl total nitrogen, nonprotein nitrogen, and NCN content in duplicate, and by SDS-PAGE. The CN%TP determined by Kjeldahl was compared with the CN%TP estimated by SDS-PAGE calculated in 2 ways: as a percentage of only intact caseins divided by TP and as a percentage of both intact caseins and CNPP divided by TP. Three milks varying in fat, lactose, TP, CN, and SP content were formulated. These milks were analyzed in duplicate for Kjeldahl total nitrogen, nonprotein nitrogen, and NCN content, and each of the NCN filtrate and NCN precipitate were analyzed in duplicate by SDS-PAGE for relative quantity (%) of CN, CNPP, and SP. We found that the estimate of CN%TP by Kjeldahl was higher than the estimate of CN%TP by SDS-PAGE that was calculated as only intact CN divided by the total of all protein bands. However, no difference was detected in the estimate of CN%TP by Kjeldahl compared with CN%TP by SDS-PAGE when CNPP were included as CN in the calculation of SDS-PAGE results. Based on SDS-PAGE results, we found that a majority (89%) of the CNPP from the milk (approximately 10.13 out of 11.41% TP) were retained in the Kjeldahl NCN precipitate. Thus, CN%TP measured by Kjeldahl underestimates the amount of proteolytic damage that has been done to CN in milk. It is important for the dairy industry to correctly and rapidly measure the extent of proteolytic damage to milk protein to correctly value milk from a product quality and yield point of view. A rapid and quantitative measure of proteolytic damage to milk protein is needed.

Determination of the efficiency of removal of whey protein from sweet whey with ceramic microfiltration membranes

Our research objective was to measure percent removal of whey protein from separated sweet whey using 0.1-µm uniform transmembrane pressure ceramic microfiltration (MF) membranes in a sequential batch 3-stage, 3× process at 50°C. Cheddar cheese whey was centrifugally separated to remove fat at 72°C and pasteurized (72°C for 15 s), cooled to 4°C, and held overnight. Separated whey (375 kg) was heated to 50°C with a plate heat exchanger and microfiltered using a pilot-scale ceramic 0.1-µm uniform transmembrane pressure MF system in bleed-and-feed mode at 50°C in a sequential batch 3-stage (2 diafiltration stages) process to produce a 3× MF retentate and MF permeate. Feed, retentate, and permeate samples were analyzed for total nitrogen, noncasein nitrogen, and nonprotein nitrogen using the Kjeldahl method. Sodium dodecyl sulfate-PAGE analysis was also performed on the whey feeds, retentates, and permeates from each stage. A flux of 54 kg/m² per hour was achieved with 0.1-µm ceramic uniform transmembrane pressure microfiltration membranes at 50°C. About 85% of the total nitrogen in the whey feed passed though the membrane into the permeate. No passage of lactoferrin from the sweet whey feed of the MF into the MF permeate was detected. There was some passage of IgG, bovine serum albumen, glycomacropeptide, and casein proteolysis products into the permeate. β-Lactoglobulin was in higher concentration in the retentate than the permeate, indicating that it was partially blocked from passage through the ceramic MF membrane.

Flux and transmission of β-casein during cold microfiltration of skim milk subjected to different heat treatments

Raw skim milk was subjected to different heat treatments: thermization (65°C, 20 s), pasteurization (72°C, 15 s), and no heat treatment (milk was microfiltered using 1.4-µm membranes at 50°C for bacteria removal; 1.4 MF). The milk (thermized, pasteurized, and 1.4 MF) was cooled and stored at 2°C until processing (at least 24 h) with cold (∼6°C) microfiltration using a benchtop crossflow pilot unit (Pall Membralox XLAB 5, Pall Corp., Port Washington, NY) equipped with 0.1-µm nominal pore diameter ceramic Membralox membrane (ET1-070, α-alumina, Pall Corp.). The flux was monitored during the process, and β-casein transmission and removal were calculated. The study aimed to indicate the conditions that should be applied to maximize β-casein passage through the membrane during cold microfiltration (5.6 ± 0.4°C) of skim milk. The proper selection of heat treatment parameters (temperature, time) of the feed before the cold microfiltration process will increase β-casein removal. It is not clear whether the difference in β-casein transmission between 1.4 MF, thermized, and pasteurized milk results from the effect of heat treatment conditions on β-casein dissociation from the casein micelles or on passage of β-casein through the membrane. The values of the major parameters (permeation flux and tangential flow velocity, through the wall shear stress) responsible for a proper membrane separation process were considerably lower than the critical values. It seems that the viscosity of the retentate has a great effect on the performance of the microfiltration membranes for protein separation at refrigerated temperatures.

Factor analysis as a tool to estimate association among individual proteins and other milk components with casein micelle size and cheese yield

ABSTRACT The present study attempted to identify individual milk proteins and other milk components that are associated with casein micelle size (CMS) and dry matter cheese yield (DMCY) using factor analysis. Here, we used 140 bulk tank milk samples from different farms. Milk composition was determined using a Fourier transform infrared equipament. The individual milk proteins were (αS-casein, β-casein, κ-casein, β-lactoglobulin and α-lactoalbumin) measured by their electrophoretic profile. The CMS was estimated by photon correlation spectroscopy, and the DMCY was determined using reduced laboratory-scale cheese production. Factor analysis partitioned the milk components into three groups that, taken together, explain 68.3% of the total variance. The first factor was defined as “CMS”, while the second as “DMCY” factor, based on their high loadings. The CMS was positively correlated with protein, casein, non-fat solids and αS-casein and negatively associated with κ-casein and β-lactoglubulin. DMCY was positively correlated with fat, protein, casein, total solids and negatively correlated with αs-casein. These results indicate that the variation of individual milk proteins may be an important aspect correlated to milk quality and cheese production.

The nonlinear effect of somatic cell count on milk composition, coagulation properties, curd firmness modeling, cheese yield, and curd nutrient recovery

The aim of this study was to investigate the relationships between somatic cell count (SCC) in milk and several milk technological traits at the individual cow level. In particular, we determined the effects of very low to very high SCC on traits related to (1) milk yield and composition; (2) coagulation properties, including the traditional milk coagulation properties (MCP) and the new curd firming model parameters; and (3) cheese yield and recovery of milk nutrients in the curd (or loss in the whey). Milk samples from 1,271 Brown Swiss cows from 85 herds were used. Nine coagulation traits were measured: 3 traditional MCP [rennet coagulation time (RCT, min), curd firming rate (k20, min), and curd firmness after 30 min (a30, mm)] and 6 new curd firming and syneresis traits [potential asymptotic curd firmness at infinite time (CFP, mm), curd firming instant rate constant (kCF, % × min(-1)), syneresis instant rate constant (kSR, % × min(-1)), rennet coagulation time estimated using the equation (RCTeq, min), maximum curd firmness achieved within 45 min (CFmax, mm), and time at achievement of CFmax (tmax, min)]. The observed cheese-making traits included 3 cheese yield traits (%CYCURD, %CYSOLIDS, and %CYWATER, which represented the weights of curd, total solids, and water, respectively, as a percentage of the weight of the processed milk) and 4 nutrient recoveries in the curd (RECFAT, RECPROTEIN, RECSOLIDS, and RECENERGY, which each represented the percentage ratio between the nutrient in the curd and milk). Data were analyzed using a linear mixed model with the fixed effects of days in milk, parity, and somatic cell score (SCS), and the random effect of herd-date. Somatic cell score had strong influences on casein number and lactose, and also affected pH; these were traits characterized by a quadratic pattern of the data. The results also showed a negative linear relationship between SCS and milk yield. Somatic cell score influenced almost all of the tested coagulation traits (both traditional and modeled), with the exceptions of k20, CFP, and kSR. Gelation was delayed when the SCS decreased (slightly) and when it increased (strongly) with respect to a value of 2, as confirmed by the quadratic patterns observed for both RCT and RCTeq. The SCS effect on a30 showed a quadratic pattern almost opposite to that observed for RCT. With respect to the CFt parameters, kCF decreased linearly as SCS increased, resulting in a linear decrease of CFmax and a quadratic pattern for tmax. Milk SCS attained significance for %CYCURD, %CYWATER, and RECPROTEIN. As the SCS increased beyond 3, we observed a progressive quadratic decrease of the water retained in the curd (%CYWATER), which caused a parallel decrease in %CYCURD. With respect to RECPROTEIN, the negative effect of SCS was almost linear. Recovery of fat and (consequently) RECENERGY was characterized by a more evident quadratic trend, with the most favorable values associated with an intermediate SCS. Together, our results confirmed that high SCS has a negative effect on milk composition and technological traits, highlighting the nonlinear trends of some traits across the different classes of SCS. Moreover, we report that a very low SCS has a negative effect on some technological traits of milk.

Milk-derived bioactive peptides inhibit human endothelial-monocyte interactions via PPAR-γ dependent regulation of NF-κB

Background

Milk-derived bioactive peptides retain many biological properties and have therapeutic effects in cardiovascular disorders such as atherosclerosis. Under inflammatory conditions the expression of endothelial cells adhesion molecules is induced, increasing monocyte adhesion to human vessel wall, a critical step in the pathogenesis of atherosclerosis. In the present work we explored the effects of milk-derived bioactive peptides on the expression of the inflammatory phenotype of human endothelial cells and their effects on monocyte adherence to endothelial cells.

Results

Treatment of endothelial cells with milk-derived hydrolysate inhibited their production of inflammatory proteins MCP-1 and IL-8 and expression of VCAM-1, ICAM-1 and E-selectin. Milk derived hydrolysate also attenuated the adhesion of human monocytes to activated endothelial cells. The effect was similar to that obtained in endothelial cells treated with troglitazone, a ligand of peroxisome proliferators-activator receptor-gamma (PPAR-γ). PPAR-γ is a transcription factor which when activated antagonises the pro-inflammatory capability of nuclear factor κB (NF-κB). We further examined whether the effects of milk-derived hydrolysates on endothelial cells may be mediated through NF-κB activation via a PPAR-γ dependent mechanism. The specific PPAR-γ inhibitor, GW9662 blocked the effects of the hydrolysate on the NF-κB-mediated chemokines and adhesion molecules expression in endothelial cells.

Conclusions

These results suggest that milk-derived bioactive peptides work as anti-atherogenic agents through the inhibition of endothelial-dependent adhesive interactions with monocytes by inhibiting the NF-κB pathway through a PPAR-γ dependent mechanism.

Electronic supplementary material

The online version of this article (doi:10.1186/s12950-014-0044-1) contains supplementary material, which is available to authorized users.

Influence of race and crossbreeding on casein micelles size

Casein (CN) micelles are colloidal aggregates of protein dispersed in milk, the importance of which in the dairy industry is related to functionality and yield in dairy products. The objective of this work was to investigate the correlation of milk CN micelles diameter from Holstein and Zebu crossbreds with milk composition (protein, fat, lactose, total and nonfat solids and milk urea nitrogen), somatic cell count (SCC), age, lactation stage and production. Average casein micelles diameters of milk samples obtained from 200 cows were measured using photon correlation spectroscopy and multiple regression analysis was used to find relationship between variables. CN micelle diameter, SCC and nonfat solids were different between animals with different Holstein crossbreed ratios, which suggests influence of genetic factors, mammary gland health and milk composition. Overall, results indicate the potential use of CN micelle diameter as a tool to select animals to produce milk more suitable to cheese production.

A peptidomic approach to biomarker discovery for bovine mastitis

Bovine mastitis is usually caused by either Gram positive or Gram negative bacteria, reducing the quantity and quality of milk produced. This investigation using capillary electrophoresis and mass spectroscopy, studied peptides in milk from cows with clinical mastitis in comparison to milk from healthy cows to identify biomarkers for mastitis. In addition, the milk peptidome from udders infected with Gram positive Staphylococcus aureus (S. aureus) or with Gram negative Escherichia coli (E. coli), was examined to assess differential diagnosis between the causative agent. Comparison of the peptidome between healthy (n=10) and mastitic milk (n=27) identified 154 peptides for a biomarker panel which in a model for diagnosis of mastitis showed 100% sensitivity and specificity. β-casein and α(s1) casein provided the majority of peptides identified in this model. The peptidome comparison of milk from mastitis cases caused by S. aureus (n=8) or E. coli (n=11) revealed a biomarker panel of 47 peptides which discriminated between cause of infection with a sensitivity of 75% and a specificity of 100%. β-casein fragments were the most common of the peptides in this model. Peptide biomarkers of milk could be used in the diagnosis of mastitis and can discriminate between these two bacterial causes.

BIOLOGICAL SIGNIFICANCE

The paper describes an innovative approach to the use of gel free proteomics to identify the peptides that are present in milk during clinical mastitis, which is a major cause of loss of production to dairy farmers worldwide. The use of capillary electrophoresis, liquid chromatography and mass spectrometry has been able to identify panels of peptides which can be used for disease diagnosis and for differential diagnosis of the causative bacteria of the infections of the mammary gland. As well as contributing to our knowledge of the pathophysiology of bovine mastitis the results could be the basis of improved detection and differential diagnosis of the disease.

Influence of casein on flux and passage of serum proteins during microfiltration using polymeric spiral-wound membranes at 50°C

Raw milk (approximately 1,800 kg) was separated at 4°C, pasteurized (at 72°C for 16s), and split into 2 batches. One batch (620 kg) was microfiltered (MF) using pilot-scale ceramic uniform transmembrane pressure Membralox membranes (model EP1940GL0.1 μA, 0.1-μm alumina; Pall Corp., East Hills, NY) to produce retentate and permeate. The permeate from the MF uniform transmembrane pressure was casein-free skim milk (CFSM). The CFSM was MF using polymeric spiral-wound (SW) membranes (model FG7838-OS0x-S, 0.3 μm; Parker-Hannifin Corp., Process Advanced Filtration Division, Tell City, IN) at a concentration factor of 3× and temperature of 50°C. Following the processing of CFSM, the second batch of skim milk (1,105 kg) was processed using the same polymeric membranes to determine how casein content in the feed material for MF with polymeric membranes affects the performance of the system. There was little resistance to passage of milk serum proteins (SP) through a 0.3-μm polyvinylidene fluoride (PVDF) SW membrane at 50°C and no detectable increase in hydraulic resistance of the membrane when processing CFSM. Therefore, milk SP contributed little, if any, to fouling of the PVDF membrane. In contrast, when processing skim milk containing a normal concentration of casein, the flux was much lower than when processing CFSM (17.2 vs. 80.2 kg/m(2) per hour, respectively) and the removal of SP from skim milk with a single-pass 3× bleed-and-feed MF system was also much lower than from CFSM (35.2 vs. 59.5% removal, respectively). Thus, when processing skim milk with a PVDF SW membrane, casein was the major protein foulant that increased hydraulic resistance and reduced passage of SP through the membrane.

Comparison of effects of dietary coconut oil and animal fat blend on lactational performance of Holstein cows fed a high-starch diet

Dietary medium-chain fatty acids (C(8:0) through C(12:0)) are researched for their potential to reduce enteric methane emissions and to increase N utilization efficiency in ruminants. We aimed to 1) compare coconut oil (CNO; ~60% medium-chain fatty acids) with a source of long-chain fatty acids (animal fat blend; AFB) on lactational responses in a high-starch diet and 2) determine the effect of different dietary concentrations of CNO on dry matter intake (DMI). In experiment 1, the control diet (CTRL) contained (dry basis) 40% forage (71% corn silage, and alfalfa hay and haylage), 26% NDF, and 35% starch. Isonitrogenous treatment diets contained 5.0% of AFB (5%-AFB), CNO (5%-CNO), or a 1-to-1 mixture of AFB and CNO (5%-AFB-CNO) and 0.8% corn gluten meal in place of corn grain. Thirty-two multiparous dairy cows (201 ± 46 d postpartum; 42.0 ± 5.5 kg/d 3.5% fat-corrected milk yield) were adapted to CTRL, blocked by milk yield, and randomly assigned to 1 of 4 treatment diets for 21 d with samples and data collected from d 15 through 21. Treatment 5%-CNO decreased DMI markedly and precipitously and was discontinued after d 5. In wk 3, 5%-AFB and especially 5%-AFB-CNO lowered total-tract NDF digested vs. CTRL (2.6 vs. 1.8 vs. 3.1 kg/d, respectively), likely because fat treatments reduced DMI and 5%-AFB-CNO impaired total-tract NDF digestibility. Milk fat concentrations were 3.10% (CTRL), 2.51% (5%-AFB), and 1.97% (5%-AFB-CNO) and correlated negatively to concentrations of C(18:2 trans-10,cis-12) in milk fat. Additionally, 5%-AFB and 5%-AFB-CNO tended to lower milk yield and decreased yields of solids-corrected milk and milk protein compared with CTRL. Fat treatments decreased milk lactose concentration, but increased milk citrate concentration. Moreover, cows fed 5%-AFB-CNO produced less solids-corrected milk than did cows fed 5%-AFB. In experiment 2, diets similar to CTRL contained 2.0, 3.0, or 4.0% CNO. Fifteen multiparous cows (219 ± 42 d postpartum; 42.1 ± 7.0 kg milk yield; mean ± SD) were blocked by DMI and randomly assigned to 1 of 3 treatment diets for an 8-d evaluation. Dietary concentration of CNO affected DMI, with the greatest depression at 4.0% CNO. Overall, dietary CNO depressed DMI and NDF digestibility of a high-starch diet compared with AFB. Feeding CNO to lactating cows equal to or greater than 2.5% decreased lactational performance or DMI.

The association of dietary intake of purine-rich vegetables, sugar-sweetened beverages and dairy with plasma urate, in a cross-sectional study

Introduction

Hyperuricemia is a strong risk factor for gout. The incidence of gout and hyperuricemia has increased recently, which is thought to be, in part, due to changes in diet and lifestyle. Objective of this study was to investigate the association between plasma urate concentration and: a) food items: dairy, sugar-sweetened beverages (SSB) and purine-rich vegetables; b) related nutrients: lactose, calcium and fructose.

Methods

A total of 2,076 healthy participants (44% female) from a population-based case-control study in Scotland (1999–2006) were included in this study. Dietary data was collected using a semi-quantitative food frequency questionnaire (FFQ). Nutrient intake was calculated using FFQ and composition of foods information. Urate concentration was measured in plasma.

Results

Mean urate concentration was 283.8±72.1 mmol/dL (females: 260.1±68.9 mmol/dL and males: 302.3±69.2 mmol/dL). Using multivariate regression analysis we found that dairy, calcium and lactose intakes were inversely associated with urate (p = 0.008, p = 0.003, p = 0.0007, respectively). Overall SSB consumption was positively associated with urate (p = 0.008), however, energy-adjusted fructose intake was not associated with urate (p = 0.66). The intake of purine-rich vegetables was not associated to plasma urate (p = 0.38).

Conclusions

Our results suggest that limiting purine-rich vegetables intake for lowering plasma urate may be ineffectual, despite current recommendations. Although a positive association between plasma urate and SSB consumption was found, there was no association with fructose intake, suggesting that fructose is not the causal agent underlying the SSB-urate association. The abundant evidence supporting the inverse association between plasma urate concentration and dairy consumption should be reflected in dietary guidelines for hyperuricemic individuals and gout patients. Further research is needed to establish which nutrients and food products influence plasma urate concentration, to inform the development of evidence-based dietary guidelines.

Effects of somatic cells on the protein profile of hard ovine cheese produced from different breeds

Bulk tank ewe's milks with low (<500,000 ml−1), medium (1,000,000–1,500,000 ml−1) and high (>2,500,000 ml−1) somatic cell counts (SCC) from three breeds were used to manufacture hard ewes’-milk cheese. Physico-chemical analysis and capillary electrophoresis of fresh cheeses and cheeses that had been ripened for 1, 2, 3 and 6 months were carried out. The results showed that high SCC levels in milk affected the moisture content of only freshly made cheeses and the pH, fat content and fat acidity of ripened cheeses. Regarding proteolysis, the levels of all β-CNs in freshly made cheeses were significantly lower as the SCC values increased and the Castellana breed was the most affected by SCC levels because a significant decrease in all α-CNs was also observed as SCC levels rose. Analysis of the casein profile by principal component analysis (PCA) revealed that there were no clear differences according the SCC up to the third month. However in the third and sixth months cheeses with low levels of SC were closely grouped and characterised by the highest levels of intact caseins. Regarding the effect of breed, the results point to a more intense proteolytic activity in the Assaf breed, whose more matured cheeses showed the highest content of casein proteolytic fragments.

Genome-wide scan to detect quantitative trait loci for milk urea nitrogen in Dutch Holstein-Friesian cows

Studies have reported genetic variation in milk urea nitrogen (MUN) between cows, suggesting genetic differences in nitrogen efficiency between cows. In this paper, the results of a genome-wide scan to identify quantitative trait loci (QTL) that contribute to genetic variation in MUN and MUN yield are presented. Two to 3 morning milk samples were taken from 1,926 cows, resulting in 5,502 test-day records. Test-day records were corrected for systematic environmental effects using a repeatability animal model. Averages of corrected phenotypes of 849 cows, belonging to 7 sire families, were used in an across-family multimarker regression approach to detect QTL. Animals were successfully genotyped for 1,341 single nucleotide polymorphisms. The QTL analysis resulted in 4 chromosomal regions with suggestive QTL: Bos taurus autosomes (BTA) 1, 6, 21, and 23. On BTA 1, 2 suggestive QTL affecting MUN were detected at 60 and 140 cM. On BTA 6, 1 suggestive QTL affecting both MUN and MUN yield was detected at 103 cM. On BTA 21, 1 suggestive QTL affecting MUN yield was detected at 83 cM. On BTA 23, 1 suggestive QTL affecting MUN was detected at 54 cM. Quantitative trait loci for MUN and MUN yield were suggestive and each explained between 2 and 3% of the phenotypic variance.

Effect of somatic cell counts on ewes' milk protein profile and cheese-making properties in different sheep breeds reared in Spain

Bulk tank ewe's milks from Assaf, Castellana and Churra breeds categorized within three different Somatic Cell Count (SCC) groups (LSCC: <500 000; MSCC: 1 000 000 to 1 500 000; and HSCC: 2 500 000 to 3 000 000 cells ml−1) were used to investigate changes in capillary electrophoresis protein profiles and cheese-making properties. The results do not reveal a significant effect of SCC on total casein contents, because the sum of β-caseins decreased as SCC increased; no statistically significant differences were observed for the sum of α-caseins, and the values of κ-casein were higher in the HSCC milk. However, the soluble proteins other than α-lactalbumin and β-lactoglobulin increased with SCC. Regarding the effect of breed, the Assaf breed had the lowest contents of κ-CN, αs1-I-CN, αs1-II-CN 1-CN, αs1-III-CN, β1-CN and β2-CN. The protein profile was significantly correlated with curd textural properties. αs1-I-CN was the most influential variant because it was positively correlated with a large number of textural parameters. Cheese yield was positively correlated with all casein variants except αs1-III-CN, showing that the milk from local breeds were more suitable for cheese-making due to their higher contents of all the casein variants. Regarding curd texture properties LSCC milk curds showed more cohesiveness, associated with its lower content of αs1-III-CN and Castellana milk curds showed the highest values for firmness owing to their higher content of αs1-I-CN.

Identification of peptides in milk as a result of proteolysis at different levels of somatic cell counts using LC MALDI MS/MS detection

The somatic cell count (SCC) in milk is associated with increasing proteolytic degradation of caseins and it has been suggested that enzymes derived from somatic cells contribute to a lower yield and poorer quality of cheese. It is essential to increase the knowledge on naturally occurring milk proteinase activities to better understand how to improve the technological quality of milk. The aim of this work was to identify peptides actually present in milk as a result of proteolysis at different levels of SCC and to assign these peptides to potential responsible proteases where possible. Peptide fractions were prepared from acid whey by ultrafiltration at a molecular cut-off value of 10 000 Da. The peptides were separated using capillary reversed phase high performance liquid chromatography (RP-HPLC) and identified by matrix-assisted laser desorption/ionization-time of flight tandem mass spectrometry (MALDI-TOF MS/MS). Peptides identified ranged in mass from 1023 to 2000 Da, and originated from αS1-, αS2- or β-casein. Possible responsible proteases that could be suggested when examining the peptide cleavage sites included plasmin, cathepsin B, D and leukocyte elastase. The results indicated that plasmin was primarily responsible for the observed proteolysis in milk at low cell count, whereas the cathepsins and elastase became implicated at elevated cell count. Specificity and activity of cathepsins and elastase has earlier mainly been studied in model systems, whereas less is known about their activities in milk itself. This is also the first indication of involvement of elastase in milk proteolysis through the unequivocal determination of cleavage sites.

Lipolysis and Proteolysis of Modified and Producer Milks Used for Calibration of Mid-Infrared Milk Analyzers

Our objective was to determine if lipolysis or proteolysis of calibration sets during shelf life influenced the mid-infrared (MIR) readings or calibration slopes and intercepts. The lipolytic and proteolytic deterioration was measured for 3 modified milk and 3 producer milk calibration sets during storage at 4 degrees C. Modified and producer milk sets were used separately to calibrate an optical filter and virtual filter MIR analyzer. The uncorrected readings and slopes and intercepts of the calibration linear regressions for fat B, fat A, protein, and lactose were determined over 28 d for modified milks and 15 d for producer milks. It was expected that increases in free fatty acid content and decreases in the casein as a percentage of true protein of the calibration milks would have an effect on the MIR uncorrected readings, calibration slopes and intercepts, and MIR predicted readings. However, the influence of lipolysis and proteolysis on uncorrected readings was either not significant, or significant but very small. Likewise, the amount of variation accounted for by day of storage at 4 degrees C of a calibration set on the calibration slopes and intercepts was also very small. Most of the variation in uncorrected readings and calibration slopes and intercepts were due to differences between the optical filter and virtual filter analyzers and differences between the pasteurized modified milk and raw producer milk calibration sets, not due to lipolysis or proteolysis. The combined impact of lipolysis and proteolysis on MIR predicted values was <0.01% in most cases.