Effects of Milk Composition and Genetic Polymorphism on Coagulation Properties of Milk

Milk samples from 31 Holstein cows of different phenotypes for β-casein, κ-casein, and β-lactoglobulin were collected monthly over the entire lactation. These samples were analyzed for total solids, fat, protein, casein fractions, lactose, urea, citric acid, somatic cell count, and pH. Rennet clotting time, rate of firming, and curd firmness as measured by a Formagraph were not significantly influenced by phenotypes for β-casein and κ-casein. Phenotype AA for β-lactoglobulin gave the best clotting time (3.91 min) and firmness of curd (36.30 mm) when compared with AB and BB phenotypes. Relative percentages of the different caseins and α-lactalbumin affected significantly rate of firming and curd firmness at cutting. Amount of κ-casein in milk was the most significant factor that affected curd firmness with a coefficient of regression of 15.96.     

Effect of milk fat concentration and gel firmness on syneresis during curd stirring in cheese-making

An experiment was undertaken to investigate the effect of milk fat level (0%, 2.5% and 5.0% w/w) and gel firmness level at cutting (5, 35 and 65 Pa) on indices of syneresis, while curd was undergoing stirring. The curd moisture content, yield of whey, fat in whey and casein fines in whey were measured at fixed intervals between 5 and 75 min after cutting the gel. The casein level in milk and clotting conditions was kept constant in all trials. The trials were carried out using recombined whole milk in an 11 L cheese vat. The fat level in milk had a large negative effect on the yield of whey. A clear effect of gel firmness on casein fines was observed. The best overall prediction, in terms of coefficient of determination, was for curd moisture content using milk fat concentration, time after gel cutting and set-to-cut time (R² = 0.95).     

Rennet coagulation of sheep milk processed by ultrafiltration at low concentration factors

The ultrafiltration (UF) of sheep milk is carried out in concentration mode in order to evaluate the variation of the rennet clotting properties of the concentrates as a function of the volumetric concentration factors up to a value of 2.0. The UF unit is equipped with 25.5 cm² of membrane surface area. The cellulose acetate laboratory – made membrane has a molecular weight cut-off of 7000 Da. The evolution pattern of the rennet clotting properties of the skimmed sheep milk feed and UF retentates was assessed by the Optigraph. A significant increase on curd firmness and rate of curd firming was detected with the increase of the protein concentration, while RCT show a tendency to increase with milk protein content. The variation of curd firmness and rate of curd firming with the protein concentration was linear and correlations were established.     

Plasminogen activation system in goat milk and its relation with composition and coagulation properties

The activity of plasmin (PL), plasminogen (PG), and plasminogen activator (PA) and their correlation with goat milk components and milk clotting parameters were investigated. Seven late-lactating Saanen goats were used to provide milk samples that were analyzed for PL, PG, and PA activity (colorimetric assay) fat, protein, noncasein nitrogen, nonprotein nitrogen, casein content, and somatic cell count (SCC). Milk clotting parameters (rennet coagulating time = coagulation time; K20 = firming rate of curd; A30 = curd firmness) were measured with a formagraph. Average milk yield and composition were similar to those previously observed in other studies. Plasmin, PG, and PA activity, expressed as units/ml, were, respectively, 20.04 +/- 0.94, 3.21 +/- 0.04, and 1154 +/- 57.61. Plasminogen activity was surprisingly low compared with other species (bovine, ovine), but it was consistent with the high activity of PA. A negative significant correlation was observed between PL and milk casein content. The correlation coefficients between PL and casein/protein ratio and PA and casein/protein ratio were negative and significant. A positive significant correlation was observed between PL and rennet clotting time and PA and rennet clotting time. Also positive was the correlation between PL and K20 and PA and K20. The plasmin activity was negatively correlated with A30. High plasmin and plasminogen activator activity in goat milk appeared to be negatively related with coagulating properties in late lactation, most probably via degradation of casein due to plasmin activity.     

Influence of Protein and Fat Contents of Ultrafiltered Milk on Rheological Properties of Gels Formed by Chymosin

Enzymatically induced gelation of milk and milk concentrated by ultrafiltration was studied with a curd firmness tester which measured transmission of oscillatory deformations through the product. Scott Blair's relationship between pseudo modulus of rigidity (G) and time after clotting (t), G = G∞ e^—_λ/t described the gelation of ultrafiltered retentates satisfactorily. Maximum gel firmness G∞, and _λ, which is the time to reach a firmness of G∞/e, were affected substantially by protein content. The effect of protein content on rates of firming of gels were evaluated at different stages of gel formation. At the onset of gelation, rates increased up to protein content 90 g kg^—1 but decreased at higher protein concentrations. At a later stage, this decrease disappeared and rates correlated with protein content. Those observations are discussed relative to effects of protein content on proteolytic and aggregation phases of milk clotting.Times from clotting to point of cutting curd were affected significantly by slight increases in protein above that in unconcentrated milk, but clotting times were not affected. Variations in fat content had inconsequential effects on test measures.     

Genetic analysis of coagulation properties,curd firming modeling,milk yield,composition, and acidity in Sarda dairy sheep

Sheep milk is an important source of food, especially in Mediterranean countries, and is used in large part for cheese production. Milk technological traits are important for the sheep dairy industry, but research is lacking into the genetic variation of such traits. Therefore the aim of this study was to estimate the heritability of traditional milk coagulation properties and curd firmness modeled on time t (CF_t) parameters, and their genetic relationships with test-day milk yield, composition (fat, protein, and casein content), and acidity in Sarda dairy sheep. Milk samples from 1,121 Sarda ewes from 23 flocks were analyzed for 5 traditional coagulation properties by lactodynamographic tests conducted for up to 60 min: rennet coagulation time (min), curd-firming time (k₂₀, min), and 3 measures of curd firmness (a₃₀, a₄₅, and a₆₀, mm). The 240 curd firmness observations (1 every 15 s) from each milk sample were recorded, and 4 parameters for each individual sample equation were estimated: rennet coagulation time estimated from the equation (RCT_eq), the asymptotic potential curd firmness (CF_P), the curd firming instant rate constant (k_CF), and the syneresis instant rate constant (k_SR). Two other derived traits were also calculated (CF_max, the maximum curd firmness value; and t_max, the attainment time). Multivariate analyses using Bayesian methodology were performed to estimate the genetic relationships of milk coagulation properties and CF_t with the other traits; statistical inference was based on the marginal posterior distributions of the parameters of concern. The marginal posterior distribution of heritability estimates of milk yield (0.16 ± 0.07) and composition (0.21 ± 0.11 to 0.28 ± 0.10) of Sarda ewes was similar to those often obtained for bovine species. The heritability of rennet coagulation time as a single point trait was also similar to that frequently obtained for cow milk (0.19 ± 0.09), whereas the same trait calculated as an individual equation parameter exhibited larger genetic variation and a higher heritability estimate (0.32 ± 0.11). The other curd firming and syneresis traits, whether as traditional single point observations or as individual equation parameters and derived traits, were characterized by heritability estimates lower than for coagulation time and for the corresponding bovine milk traits (0.06 to 0.14). Phenotypic and additive genetic correlations among the 11 technological traits contribute to describing the interdependencies and meanings of different traits. The additive genetic relationships of these technological traits with the single test-day milk yield and composition were variable and showed milk yield to have unfavorable effects on all measures of curd firmness (a₃₀, a₄₅, a₆₀, CF_P, and CF_max) and t_max, but favorable effects on both instant rate constants (k_CF and k_SR). Milk fat content had a positive effect on curd firmness traits, especially on those obtained from CF_t equations, whereas the negative effects on both coagulation time traits were attributed to the milk protein and casein contents. Finally, in view of the estimated heritabilities and additive genetic correlations, enhancement of technological traits of sheep milk through selective breeding could be feasible in this population.     

Short communication: Factors affecting coagulation properties of Mediterranean buffalo milk

The aim of this study was to investigate sources of variation of milk coagulation properties (MCP) of buffalo cows. Individual milk samples were collected from 200 animals in 5 herds located in northern Italy from January to March 2010. Rennet coagulation time (RCT, min) and curd firmness after 30 min from rennet addition (a₃₀, mm) were measured using the Formagraph instrument (Foss Electric, Hillerød, Denmark). In addition to MCP, information on milk yield, fat, protein, and casein contents, pH, and somatic cell count (SCC) was available. Sources of variation of RCT and a₃₀ were investigated using a linear model that included fixed effects of herd, days in milk (DIM), parity, fat content, casein content (only for a₃₀), and pH. The coefficient of determination was 51% for RCT and 48% for a₃₀. The most important sources of variation of MCP were the herd and pH effects, followed by DIM and fat content for RCT, and casein content for a₃₀. The relevance of acidity in explaining the variation of both RCT and a₃₀, and of casein content in explaining that of a₃₀, confirmed previous studies on dairy cows. Although future research is needed to investigate the effect of these sources of variation on cheese yield, findings from the present study suggest that casein content and acidity may be used as indicator traits to improve technological properties of buffalo milk.     

Milk protein fractions strongly affect the patterns of coagulation,curd firming,and syneresis

The aim of this study was to assess the role of milk protein fractions in the coagulation, curd firming, and syneresis of bovine milk. Analyses were performed on 1,271 individual milk samples from Brown Swiss cows reared in 85 herds classified into 4 types of farming systems, from the very traditional (tied cows, feed manually distributed, summer highland pasture) to the most modern (loose cows, use of total mixed rations with or without silage). Fractions α_S1-casein (CN), α_S2-CN, β-CN, κ-CN, β-lactoglobulin (LG), and α-lactalbumin (LA) and genotypes at CSN2, CSN3, and BLG were obtained by reversed-phase HPLC. The following milk coagulation properties were measured with a lactodynamograph, with the testing time extended to 60 min: rennet coagulation time (RCT, min), curd firming time (min), and curd firmness at 30 and 45 min (mm). All the curd firmness measures recorded over time (total of 240 observations/sample) were used in a 4-parameter nonlinear model to obtain parameters of coagulation, curd firming, and syneresis: RCT estimated from the equation (min), asymptotic potential curd firmness (mm), the curd firming and syneresis instant rate constants (%/min), and the maximum curd firmness value (CF_max, mm) and the time taken to reach it (min). All the aforementioned traits were analyzed with 2 linear mixed models, which tested the effects of the protein fractions expressed in different ways: in the first, quantitative model, each protein fraction was expressed as content in milk; in the second, qualitative model, each protein fraction was expressed as a percentage of total casein content. Besides proteins, additional nuisance parameters were herd (included as a random effect), daily milk production (only for the quantitative model), casein content (only for the qualitative model), dairy system, parity, days in milk, the pendulum of the lactodynamograph, and the CSN2, CSN3, and BLG genotypes. Both α_S1-CN and β-CN showed a clear and favorable effect on CF_max, where the former effect was almost double the latter. Milk coagulation ability was favorably affected by κ-CN, which reduced both the RCT and RCT estimated from the equation, increased the curd firming and syneresis instant rate constants, and allowed a higher CF_max to be reached. In contrast, α_S2-CN delayed gelation time and β-LG worsened curd firming, both resulting in a low CF_max. The results of this study suggest that modification of the relative contents of specific protein fractions can have an enormous effect on the technological behavior of bovine milk.     

Variation in Coagulation Properties of Milk from Individual Cows,

Milk samples from 50 Holstein cows were tested monthly for 10 mo for total protein, casein, fat, somatic cells, and pH. A Formagraph was used to measure chymosin coagulation properties. Significant variations in coagulation time and curd firmness were observed in relation to period of lactation, individual cows, and milk pH. A high negative correlation coefficient (?.86) was observed between coagulation time and curd firmness measured 30 min after addition of chymosin. The mean coagulation time generally increased as lactation progressed and milk yield decreased. Curd firmness was generally greatest in midlactation samples.Milk from 38% of the cows did not coagulate in 30 min 1 mo prior to their dry periods. The frequency of failure to coagulate was 68% in winter and 32% in fall. Milk pH was the most significant factor that affected coagulation time and curd firmness. Simulated cheese making procedures were utilized to estimate recovery of fat and protein in curd. Curd yield calculated from the recovery data ranged from 5.4 to 14% with a mean of 9.2%.     

High-pressure-induced changes in the rennet coagulation properties of bovine milk

The mechanism of high-pressure (HP)-induced changes in rennet coagulation properties of milk, particularly the role of whey protein-casein micelle associations, was studied. Treatment at 100 or 250 MPa reduced the rennet coagulation time (RCT) of raw skimmed bovine milk, compared with untreated milk. Treatment at 400 MPa had little effect, but at 600 MPa, RCT increased considerably. HP-induced increases in RCT did not occur in serum protein-free milk or milk treated with the sulphydryl-oxidising agent KIO₃, which prevents association of denatured β-lactoglobulin with casein micelles. Treatment at 5 or 10 °C at 250–600 MPa resulted in shorter RCT than treatment at 20 °C. In milk without KIO₃, coagulum strength was highest after treatment at 250 or 400 MPa, whereas in milk with KIO₃ it was highest after treatment at 400 MPa. These results indicate the significance of HP-induced association of whey proteins with casein micelles for rennet coagulation properties of milk.     

Cheese made from instant infusion pasteurized milk: Rennet coagulation,cheese composition,texture and ripening

Milk subjected to instant infusion pasteurization (IIP) at 72 °C, 100 °C and 120 °C (holding time 0.2 s) exhibited increased rennet coagulation time and decreased curd firming rate for increasing heat treatment temperature, when compared with raw or high temperature short time pasteurized (HTST) milk. However, addition of 4.5 mm or 9.0 mm of calcium restored the impaired rennet coagulation ability. Open texture cheeses produced from IIP milk (100 °C and 120 °C) contained significantly more moisture, had lower pH and shorter texture than similar cheese from IIP at 72 °C and HTST pasteurized milk. Cheese ripening was also affected by heat treatment, and different patterns of casein breakdown and peptide formation resulted from cheeses made from milk treated to IIP at 100 °C and 120 °C compared with cheeses made using IIP at 72 °C or HTST.     

Interactions of Calcium,pH, Temperature,and Chymosin During Milk Coagulation,

Holstein milk samples with good and poor chymosin-coagulation characteristics were coagulated in the Formagraph using different combinations of five levels of chymosin, three pH, and three temperatures in the presence and absence of .02% added calcium chloride.All the main factors significantly altered both coagulation time and curd firmness. Multiple comparisons of mean coagulation times showed that lower concentrations of chymosin (.01, .02, and .03 rennin units/ml milk) were significantly different in altering coagulation time and were different from higher concentrations (.04 and .05 rennin units/ml milk). The three pH produced significantly different mean coagulation times. Addition of more than .02 rennin units/ml milk was not necessary for adequate curd firmness in 30 min after chymosin addition where the pH of the milk was 6.4 or lower. Addition of .02% calcium chloride to milk was not necessary for adequate curd firmness 30 min after chymosin addition if other milk coagulation factors were adequately adjusted (pH ≤ 6.4; chymosin concentration = .02 rennin unit/ml milk; temperature = 37°C).     

Grazing season and forage type influence goat milk composition and rennet coagulation properties

Two different types of pasture (cultivated and rangeland) and 2 different hay qualities (high and low quality) were examined for their effects on goat milk composition and rennet coagulation properties. Furthermore, the effect of dietary treatments in both the early and late grazing season was studied. As lactation stage is known to influence milk composition, the goats in the early and late grazing season were in the same lactation stage at the start of the experiment. The milk composition was influenced both by dietary treatment and season. Milk from goats on pasture was superior to those on hay by containing a higher content of protein and casein, and the goats on cultivated pasture had the highest milk yield. Casein composition was significantly influenced by forage treatment. Goats grazing on cultivated pasture had higher contents of α_s1-casein and also of κ-casein compared with the other treatments, whereas goats grazing on rangeland had the highest content of β-casein. Factors such as milk yield, casein micelle size, α_s2-casein, and calcium content were reduced in late compared with early season. More favorable rennet coagulation properties were achieved in milk from the early grazing season, with shorter firming time and higher curd firmness compared with milk from the late grazing season, but the firming time and curd firmness were not prominently influenced by forage treatment. The content of α_s2-casein and calcium in the milk affected the firming time and the curd firmness positively. The influence of season and forage treatment on especially milk yield, casein content, and rennet coagulation properties is of economic importance for both the dairy industry and goat milk farmers.     

Associations between pathogen-specific cases of subclinical mastitis and milk yield,quality, protein composition,and cheese-making traits in dairy cows

The aim of this study was to investigate associations between pathogen-specific cases of subclinical mastitis and milk yield, quality, protein composition, and cheese-making traits. Forty-one multibreed herds were selected for the study, and composite milk samples were collected from 1,508 cows belonging to 3 specialized dairy breeds (Holstein Friesian, Brown Swiss, and Jersey) and 3 dual-purpose breeds of Alpine origin (Simmental, Rendena, and Grey Alpine). Milk composition [i.e., fat, protein, casein, lactose, pH, urea, and somatic cell count (SCC)] was analyzed, and separation of protein fractions was performed by reversed-phase high performance liquid chromatography. Eleven coagulation traits were measured: 5 traditional milk coagulation properties [time from rennet addition to milk gelation (RCT, min), curd-firming rate as the time to a curd firmness (CF) of 20 mm (k₂₀, min), and CF at 30, 45, and 60 min from rennet addition (a₃₀, a₄₅, and a₆₀, mm)], and 6 new curd firming and syneresis traits [potential asymptotical CF at an infinite time (CF_P, mm), curd-firming instant rate constant (k_CF, % × min^?1), curd syneresis instant rate constant (k_SR, % × min^?1), modeled RCT (RCT_eq, min), maximum CF value (CF_max, mm), and time at CF_max (t_max, min)]. We also measured 3 cheese yield traits, expressing the weights of total fresh curd (%CY_CURD), dry matter (%CY_SOLIDS), and water (%CY_WATER) in the curd as percentages of the weight of the processed milk, and 4 nutrient recovery traits (REC_PROTEIN, REC_FAT, REC_SOLIDS, and REC_ENERGY), representing the percentage ratio between each nutrient in the curd and milk. Milk samples with SCC > 100,000 cells/mL were subjected to bacteriological examination. All samples were divided into 7 clusters of udder health (UH) status: healthy (cows with milk SCC < 100,000 cells/mL and uncultured); culture-negative samples with low, medium, or high SCC; and culture-positive samples divided into contagious, environmental, and opportunistic intramammary infection (IMI). Data were analyzed using a linear mixed model. Significant variations in the casein to protein ratio and lactose content were observed in all culture-positive samples and in culture-negative samples with medium to high SCC compared to normal milk. No differences were observed among contagious, environmental, and opportunistic pathogens, suggesting an effect of inflammation rather than infection. The greatest impairment in milk quantity and composition, clotting ability, and cheese production was observed in the 2 UH status groups with the highest milk SCC (i.e., contagious IMI and culture-negative samples with high SCC), revealing a discrepancy between the bacteriological results and inflammatory status, and thus confirming the importance of SCC as an indicator of udder health and milk quality.     

Breed of cow and herd productivity affect milk composition and modeling of coagulation,curd firming,and syneresis

Milk coagulation properties (MCP) have been widely investigated in the past using milk collected from different cattle breeds and herds. However, to our knowledge, no previous studies have assessed MCP in individual milk samples from several multi-breed herds characterized by either high or low milk productivity, thereby allowing the effects of herd and cow breed to be evaluated independently. Multi-breed herds (n = 41) were classified into 2 categories based on milk productivity (high vs. low), defined according to the average milk net energy yielded daily by lactating cows. Milk samples were taken from 1,508 cows of 6 different breeds: 3 specialized dairy (Holstein-Friesian, Brown Swiss, Jersey) and 3 dual-purpose (Simmental, Rendena, Alpine Grey) breeds, and analyzed in duplicate (3,016 tests) using 2 lactodynamographs to obtain 240 curd firming (CF) measurements over 60 min (1 every 15 s) for each duplicate. The 5 traditional single-point MCP (RCT, k₂₀, a₃₀, a₄₅, and a₆₀) were yielded directly by the instrument from the available CF measures. All 240 CF measures of each replicate were also used to estimate 4 individual equation parameters: RCT estimated according to curd firm change over time modeling (RCT_eq), asymptotic potential curd firmness (CF_P), curd firming instant rate constant (k_CF), and syneresis instant rate constant (k_SR) and 2 derived traits: maximum curd firmness achieved within 45 min (CF_max) and time at achievement of CF_max (t_max) by curvilinear regression using a nonlinear procedure. Results showed that the effect of herd-date on traditional and modeled MCP was modest, ranging from 6.1% of total variance for k₂₀ to 10.7% for RCT, whereas individual animal variance was the highest, ranging from 32.0% for t_max to 82.5% for RCT_eq. The repeatability of MCP was high (>80%) for all traits except those associated with the last part of the lactodynamographic curve (i.e., a₆₀, k_SR, k_CF, and t_max: 57 to 71%). Reproducibility, taking into account the effect of instrument, was equal to or slightly lower than repeatability. Milk samples collected in farms characterized by high productivity exhibited delayed coagulation (RCT_eq: 18.6 vs. 16.3 min) but greater potential curd firmness (CF_P: 76.8 vs. 71.9 mm) compared with milk samples collected from low-productivity herds. Parity and days in milk influenced almost all MCP. Large differences in all MCP traits were observed among breeds, both between specialized and dual-purpose breeds and within these 2 groups of breeds, even after adjusting for milk quality and yield. Milk quality and MCP of samples from Jersey cows, and coagulation time of samples from Rendena cows were better than in milk from Holstein-Friesian cows, and intermediate results were found with the other breeds of Alpine origin. The results of this study, taking into account the intrinsic limitation of this technique, show that the effects of breed on traditional and modeled MCP are much greater than the effects of herd productivity class, parity, and DIM. Moreover, the variance in individual animals is much greater than the variance in individual herds within herd productivity class. It seems that improvement in MCP depends more on genetics (e.g., breed, selection) than on environmental and management factors.     

Yield and functionality of Cheddar cheese as influenced by homogenization of cream

Cheese milk was standardized (casein-to-fat ratio of 0.7) by blending 0.64% fat milk and 35% fat cream. Cream was homogenized at 0/0 MPa (CO), 3.5/3.5 MPa (H05), 6.9/3.5 MPa (H10) or 10.4/3.5 MPa (H15). Cream homogenization did not influence rennet-clotting time, but it increased rate of curd firming and increased curd firmness of cheese milk. Moisture and salt in moisture phase of cheese increased with homogenization. Moisture (37%) and salt (1.5%) adjusted yield increased 1.42, 3.44 and 3.85% in H05, H10 and H15, respectively, over CO. Homogenized treatment cheeses melted faster with age. Free oil in 1 week old cheeses was lowest in H10 and highest in H05 and increased in all treatments with age. Cheese hardness was not influenced by homogenization but decreased with age. Cheeses with homogenized cream had improved body and texture and flavor. Cream homogenized at 6.9/3.5 MPa was optimal for enhancing Cheddar cheese yield and functionality.     

Evaluation of on-line optical sensing techniques for monitoring curd moisture content and solids in whey during syneresis

This study focuses on the prediction ability of several optical sensing techniques, namely single wavelength (980 nm), broad spectrum and colour coordinates, for monitoring key syneresis indices during cheese manufacture. Three series of trials were undertaken in which milk gel was cut and stirred in an 11 L cheese vat. Three full factorial designs were employed with experimental variables consisting of: (i) three curd stirring speeds and three cutting programmes; (ii) three milk fat levels and three gel firmness levels at cutting; and (iii) two milk protein levels and three fat:protein ratio levels in the respective experiments. Models developed using the range of techniques investigated demonstrated that an on-line visible–NIR sensor was able to predict curd moisture content. However, the broad spectrum technique was the only one capable of predicting whey solids. The findings show that on-line sensing techniques can significantly improve the control of curd moisture content in cheese factories, across the range of experimental variables used in this study.     

Milk Coagulation Properties and Milk Protein Genetic Variants of Three Cattle Breeds/Types in Sri Lanka

Milk coagulation is the primary step in the development of most dairy products. Raw milk from individual cows and different breeds exhibit distinct coagulation capacities. This variation is largely influenced by milk protein genetic variants. The aim of the present study was to evaluate differences in coagulation properties between milk obtained from three cattle breeds/types found in Sri Lanka. A total of 90 milk samples (400 mL from each individual) were collected from two Sri Lankan cattle breeds/types (Thamankaduwa White/TW and Local/“Batu” cattle) and one European cattle breed (Friesian). Collected samples were subjected to enzymatic coagulation using commercial rennet source (Chymax®, Christian Hansen Standard, Denmark) and lactic acid bacteria (LAB) coagulation using a commercial starter culture(YFL 8 12,Christian Hansen Standard, Denmark) to determine milk coagulation properties. Different properties of milk coagulum such as yield, curd firmness, syneresis and rheological properties were evaluated. The biochemical composition (lactose, protein, fat, solid-non-fat) of milk samples were determined. Capillary Zone Electrophoresis (CZE) method was used to determine milk protein genetic variants. Experimental design was Nested Completely Randomized Design with three treatments. Milk coagulation time and curd firmness after enzymatic-coagulation were not significantly different (p>0.05) among the breeds. Coagulum yield was significantly higher (p<0.05) for the TW type than that of other breeds. Coagulum yield was negatively correlated with β-caseinA1 and α-lactalbumin in both enzymatic (-0.58) and LAB coagulation (-0.69). Coagulum yield was positively correlated (p<0.05) with β-casein B variant (0.70), protein (0.34) and lactose (0.36) contents. Meltability value was weakly and positively (p<0.05) correlated (0.34) with fat content of milk. Overall results indicate that there is a significant correlation between milk coagulation properties and milk protein genetic variants in three cattle breeds/types considered in the current study. TW type is the unique among studied breeds in terms of coagulation properties and milk protein genetic variants.     

Immunochromatographic lateral-flow test strip for the rapid detection of added bovine rennet whey in milk and milk powder

An immunochromatographic lateral-flow test dipstick test was developed for the fast detection of bovine rennet whey in liquid milk and milk powder. The test is based on the binding of casein glycomacropeptide (cGMP) by two specific anti-bovine κ-casein monoclonal antibodies and has a visual detection limit of around 15 ng mL^?1 for cGMP and 1% (v/v) for rennet whey in milk using standards and spiked samples. The dipstick performance was evaluated in a collaborative trial using skim milk powder and raw, pasteurized and UHT milk. The suitability of the dipstick was demonstrated in comparison with gel permeation-high performance liquid chromotography and a colorimetric method, by analysing 60 raw milk samples collected from farms in Brazil. The dipstick results correlated well with the HPLC results and were more reliable than those obtained with the colorimetric method. The dipstick test correctly identified all raw milk samples with a rennet whey content above 4%.     

Interactions between bacteria type,proteolysis of casein and physico-chemical properties of bovine milk

The effects of separate infection with four major pathogens frequently associated with the occurrence of subclinical mastitis in cows (Staphylococcus aureus, S. chromogenes, Escherichia coli and Streptococcus dysgalactiae) on milk quality for cheese production were studied for quarters of the same animal. Infection increased somatic cell count (SCC), modified leucocyte distribution, decreased lactose concentration and increased proteolysis of casein. Regardless of bacteria type, the plasmin activity in milk from the infected glands increased ∼2 fold compared with uninfected quarters. These changes were associated with increased rennet clotting time and decreased curd firmness for milk from infected glands, indicating that milk quality for cheese production was negatively affected by infection. Although the general pattern of bacterial invasion was similar, each type of bacteria elicited the above-described responses in a specific manner. SCC, commonly used by the dairy industry as a measure of milk hygienic quality, provided the poorest prediction of milk quality for cheese production in comparison to indices of proteolysis of casein.