Rennet Coagulation Properties Of Milk Research Articles

Rennet coagulation properties of milk in the presence of MFGM fragments isolated from raw – and pasteurised-cream buttermilk

Milk fat globule membrane (MFGM) fragments were isolated from raw- and pasteurised-cream buttermilks to determine their impact on the rennet coagulation properties of milk. These MFGM fragments were recovered by ultracentrifugation after casein micelle dissociation using sodium citrate. This procedure was also applied to raw skim milk as a control. More protein was recovered from the two types of buttermilk than from the skim milk upon centrifugation. This protein was mostly MFGM, but significant amounts of caseins and whey proteins were also recovered. This suggests that the churning of cream induces changes in these proteins, favouring their sedimentation upon ultracentrifugation. The isolated material was suspended in reconstituted skim milk, and rennet coagulation kinetics and gel contraction capacity were measured. The MFGM fragments isolated from buttermilk impaired rennet gel formation and reduced gel contraction capacity, but these effects were not related to the cream pasteurisation treatment.

Effects of milk protein polymorphism and composition, casein micelle size and salt distribution on the milk coagulation properties in Norwegian Red cattle

Effects of milk protein polymorphism and composition, casein micelle size and salts distribution on the coagulation properties of milk from 99 Norwegian Red cattle (NRF) were studied. Genetic variants of αS1-casein (CN), β-CN, κ-CN and β-lactoglobulin (LG) affected rennet coagulation properties of milk. Significant effects of κ-CN and the composite genotype αS1-β-κ-CN were observed on acid coagulation properties. Relative concentrations of milk proteins were significantly affected by individual casein genotypes and the composite genotype of αS1-β-κ-CN while, the relative concentration of β-LG was only affected by β-LG genotypes. The salts distribution in milk and the concentration of milk proteins affected both rennet and acid coagulation properties. Milk protein genotypes associated with better rennet coagulation, impaired the acid coagulation properties. However, αS1-β-κ-CN BB-A1A2-BE and BB-A2A2-BB were associated with poor rennet and acid coagulation properties. Breeding programs should focus on decreasing these genotypes in NRF cattle.

Effect of summer season on milk protein fractions in Holstein cows

Milk characteristics are affected by heat stress, but very little information is available on changes of milk protein fractions and their relationship with cheesemaking properties of milk. The main objective of the study was to evaluate the effect of hot season on milk protein fractions and cheesemaking properties of milk for Grana Padano cheese production. The study was carried out in a dairy farm with a cheese factory for transforming the milk to Grana Padano cheese. The study was carried out from June 2012 to May 2013. Temperature and relative humidity of the inside barn were recorded daily during the study period using 8 electronic data loggers programmed to record every 30min. Constant managerial conditions were maintained during the experimental periods. During the experimental period, feed and diet characteristics, milk yield, and milk characteristics were recorded in summer (from June 29 to July 27, 2012), winter (from January 25 to March 8, 2013), and spring (from May 17 to May 31, 2013). Milk yield was recorded and individual milk samples were taken from 25 cows selected in each season during the p.m. milking. Content of fat, proteins, caseins (CN), lactose and somatic cell count (SCC), titratable acidity, and milk rennet coagulation properties were determined on fresh samples. Milk protein fraction concentrations were determined by the sodium dodecyl sulfate-PAGE. Data were tested for nonnormality by the Shapiro-Wilk test. In case of nonnormality, parameters were normalized by log or exponential transformation. The data were analyzed with repeated measures ANOVA using a mixed model procedure. For all the main milk components (fat, protein, total solids, and solids-not-fat), the lowest values were observed in the summer and the greatest values were observed in the winter. Casein fractions, with the exception of γ-CN, showed the lowest values in the summer and the greatest values in the winter. The content of IgG and serum albumin was greater in summer than in the winter and spring. A mild effect of season was observed for milk SCC, with greater values in summer than in the winter and spring. A worsening of milk coagulation properties was observed in summer season. The alteration of cheesemaking properties during hot season seems strictly linked with changes of milk protein fractions mainly with the decrease of αS-CN and β-CN and the increase of undefined proteins.

Glycosylation of κ-casein: Genetic and nongenetic variation and effects on rennet coagulation properties of milk

The aims of this study were to investigate genetic and nongenetic variation in the degree of glycosylation of κ-casein (κ-CN) and to estimate the effects of glycosylated (G-κCN) and unglycosylated (U-κCN) κ-CN contents on milk coagulation properties of Simmental cows. Measures of contents of the main casein fractions, G-κCN, and U-κCN, and assessment of genotypes at CSN2, CSN3, and BLG were obtained by reversed-phase HPLC analysis of 2,015 individual milk samples. Content of total κ-CN (κ-CNtot, g/L) was the sum of G-κCN and U-κCN, and the glycosylation degree of κ-CN (GD) was measured as the ratio of G-κCN to κ-CNtot. Rennet coagulation time (RCT) and curd firmness were measured by using a computerized renneting meter. Measures of curd firmness were adjusted for RCT before statistical analysis. Variance components of κ-CNtot, G-κCN, U-κCN, and GD were estimated by Bayesian procedures and univariate linear models that included the class effects of the herd-test-day, parity, days in milk, genotypes at milk protein genes, and animal. These class effects, those of G-κCN, U-κCN, and content of other caseins, and the linear effect of milk pH were accounted for by models investigating the influence of κ-CN glycosylation on coagulation properties. The GD ranged from 22 to 76%, indicating that variation in G-κCN depends on the variation both in κ-CNtot and in the efficiency of κ-CN glycosylation. Genotype CSN3 BB exhibited high G-κCN and U-κCN relative to that of CSN3 AA. Heritability of G-κCN, U-κCN, and GD was high and ranged from 0.46 to 0.56. A large proportion of the additive genetic variation in G-κCN and U-κCN was attributable to influence of CSN and BLG, but these genes did not affect variation in GD, and across-genotypes differences in the trait were small or trivial. Average RCT of the milk class having the highest G-κCN was, on average, 2min (standard deviation 0.5) shorter than that of the lowest class. Conversely, U-κCN and content of other caseins were not associated with any effect on RCT, except for a slight delay in coagulation when U-κCN was very high. Curd firmness increased when the contents of both κ-CN fractions and other caseins increased. This study provides evidence that the positive association between RCT and κ-CN content is exclusively attributable to the glycosylated fraction of the protein. Because exploitable additive genetic variation in G-κCN exists, improvement of κ-CN composition through selective breeding might be an effective way to enhance milk coagulation properties.

RENNETABILITY OF CHEESE‐MAKING MILK PROCESSED BY NONTHERMAL TECHNOLOGIES

ABSTRACTHeat treatments (HT) modify the renneting properties of raw milk, hence nonthermal technologies seem to be a good option to ensure the microbial quality of milk without modifying its renneting properties. The effect of pulsed electric fields (PEF) and high hydrostatic pressure (HHP) on the rennet coagulation properties of milk was compared with the effect caused by HT. Milk was processed by HHP (400 and 500 MPa from 0 to 20 min) and PEF (36 and 42 kV/cm for up to 64 pulses). HHP reduced the rennet coagulation time (RCT) of milk to ∼60% of the RCT of raw milk. Contrarily, PEF and HT increased RCT in ∼10%. Gels made from HHP milk presented G′ values of 170 Pa after 20 min, raw milk reached only 50 Pa after 60 min, and PEF and HT showed lower G′ values. HHP increases rennet coagulation efficiency, whereas PEF milk behaves similarly than raw milk.PRACTICAL APPLICATIONSNonthermal technologies have been suggested as a means to ensure the microbiological safety of milk without modifying its nutritional and technical attributes, and as a way to enhance its various functional properties. High hydrostatic pressure and pulsed electric field treatments applied in this study modified the renneting properties of milk, providing as a useful tool for the redesigning of cheese‐making processes. Rheological data presented in this paper clearly characterize the formation of curds out of milk treated with nonthermal treatments over milk proteins might result in the development of novel cheeses with different textures, flavors and nutritional content.

Rennet coagulation properties of milk in the presence of oil droplets stabilised by a combination of sodium caseinate and whey protein isolate

This manuscript describes the in situ investigation of the rennet-induced aggregation of skim milk recombined with emulsion droplets stabilised with whey protein isolate (WPI) and sodium caseinate (NaCas) in isolation or in combination. The experiments were conducted with two levels of rennet as well as with and without added CaCl2. Diffusing wave spectroscopy and small deformation rheology were used to follow the gelation behaviour. In addition, scanning electron microscopy was employed to observe changes in the aggregation state of the oil droplets. We report that the presence of WPI-stabilised droplets did not alter the gelation behaviour of the casein micelles in recombined milks, even in the presence of added CaCl2. In contrast, NaCas-stabilised droplets in solution impaired the rennetability of the recombined milk, even after the addition of CaCl2. The mixture of both proteins at the interface was also investigated. When the WPI covering the fat droplets was gradually and systematically substituted by NaCas, any amount over 30% also impaired the rennetability of the milks. It was speculated that the increased steric repulsion of the oil droplets in conjunction with an increase in NaCas present in the serum phase in the recombined milks were the most likely contributors to the impaired rennetability of the casein micelles.

Extreme frequencies of the αs1-casein “null” variant in milk from Norwegian dairy goats – Implications for milk composition, micellar size and renneting properties

Caprine αs1-casein polymorphism is one of the key factors which determines important technological properties of milk, such as rennetability and cheese yield. The indigenous Norwegian goat breed is characterized by a remarkably high frequency (>70%) of a “null” variant of αs1-casein unique to this population. This mutation, referred to as the exon 12 D allele, involves a single base deletion in exon 12 of the αs1-casein gene. The aim of this study was to provide more detailed information on how αs1-casein polymorphism affects composition and rennet coagulation properties of milk from Norwegian dairy goats. Class of αs1-casein significantly affected milk composition; crude protein, casein and pH. The mean casein micelle size was larger in milks containing αs1-casein “null” variant when compared to “strong” milks; in contrast, the heat-induced changes in micelle size appeared to be least pronounced in this group. Compositional differences between “strong” and “null” milks may explain these differences. αs1-Casein class had a significant effect on gel strength recorded 30 min after the addition of rennet, with the “strong” milks giving the greatest firmness. However, a considerable fraction of the milk samples in this study were unable to form a strong clot, regardless of the αs1-casein variant. These results indicate that environmental and compositional factors not considered in this study may be important in the curd formation process.

Effect of temperature and pulsed electric field treatment on rennet coagulation properties of milk

The objective of this study was to determine the coagulation properties of pulsed electric field (PEF) treated milk compared with raw and thermally pasteurized milk. PEF treatment was achieved in a continuous chamber using a bipolar square waveform. The maximum 30 kV/cm electric field intensity ( E), 120 pulses and up to 50 °C treatment temperatures were applied. Dynamic rheological test was conducted to analyze milk coagulation properties. Results indicated that increased E, temperature, and pulse number ( N) significantly affected milk coagulation properties. However, in most cases, PEF treated milk showed better rennetability compared to thermally pasteurized milk within the experimental range. Results showed that PEF combined mild heat could be a potential pasteurization method for milk destined for cheese production.

The effect of milk protein contents on the rennet coagulation properties of milk from individual dairy cows

The objective of this study was to investigate the effect of milk proteins on rennet coagulation properties. Milk samples ( n = 516) were taken from 54 cows once a month during one full lactation period and analysed for rennet coagulation properties, and for contents of α S1-, α S2-, β- and κ-casein, and β-lactoglobulin. The contents of the analysed milk proteins and the relative contents of different caseins (Cn) in total casein were significantly influenced by sampling month, breed, and the month of lactation. An increase in milk protein, casein, casein fractions, and the casein number decreased the rennet coagulation time of milk and increased curd firmness. Milk formed a firmer curd when the relative content of α S1- and β-Cn in total casein was lower, or the relative content of κ-Cn in total casein was higher. Higher values of κ-Cn:β-Cn and κ-Cn:α S-Cn ratios had a positive effect on curd firmness.

A comparison of the methods for determination of the rennet coagulation properties of milk

The objective of the present study was to compare two methods for measuring the rennet coagulation properties of milk: the Formagraph, and the Optigraph. The parameters used to describe rennet coagulation of 81 milk samples were rennet coagulation time (RCT, Formagraph, and R, Optigraph) and curd firmness 30 min after the addition of rennet (E30, Formagraph, and A30, Optigraph). New Optigraph system recipes were found: R slope = 1.784 and R offset = − 2.303. Using the above Optigraph system recipes, no statistically significant differences were found in rennet coagulation time measurements in either of the studied methods. Regarding curd firmness, the best approximation to describe the relationship between the methods was polynomial: E30= − 0.0357*A30 2+2.8795*A30 −5.2991 (R 2 =0.925). Such strong correlations indicate that the two techniques for detecting milk coagulation properties are comparable and that the data obtained by these methods allow for data interpretation in studies using either method.

Effect of heat treatment at alkaline pH on the rennet coagulation properties of skim milk

Reconstituted skim milk was heated at 90 °C for 30 s at pH values ranging from 6.6 to 8.1, stored overnight at 5 °C then renneted at pH values ranging from 6.2 to 6.6. The heat-induced disimprovement of the rennet coagulation properties of the milk (longer rennet coagulation time and lower gel firmness) were partially reduced as heat-treatment pH increased, except at pH 6.6. These properties were related to the increased heat-induced dissociation of micellar κ-casein and subse- quent formation of serum, rather than micelle-bound, heat-induced whey protein/κ-casein aggrega- tes. It was postulated that such distribution of the denatured whey protein and κ-casein slightly reduced the detrimental effects of heating on the enzymatic coagulation, as well as helped earlier destabilisation of the micelles. These results are discussed with respect to the amplitude of the effect of the heat-treatment pH, as well as the side effects of alkalinisation and heat treatment on casein dissociation. whey protein / heat treatment / rennet coagulation / pH

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 beta-lactoglobutin with casein micelles. Treatment at 5 or 10 degrees C at 250-600 MPa resulted in shorter RCT than treatment at 20 degrees 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. (c) 2005 Elsevier Ltd. All rights reserved.

Effect of β-casein concentration in cheese milk on rennet coagulation properties, cheese composition and cheese ripening

Effects of the use of a β-casein powder to enrich cheese milk on rennet coagulation properties of milk, cheese composition and cheese ripening were investigated. Casein content of control milk was 2.5%, whereas that for the three enriched milks was adjusted with β-casein powder at 2.7%, 2.9% and 3.1%. The β-casein to α-casein ratio of these cheese milks was, respectively, 0.70, 0.79, 0.89 and 0.99. Rennet coagulation properties were related not only to casein concentration but also to the proportion of β-casein and α s-casein presents in milks. Milk with higher concentration of β-casein had poorer coagulation properties. Cheeses could be produced by using a miniature cheese making process. Moisture, ash and calcium contents decreased, while protein content and β-casein increased in cheese as casein and β-casein concentration increased in milk. As a result, hardness was higher in enriched cheeses than in control cheese. During cheese ripening, α-casein was hydrolyzed, but the rate of degradation of α-casein decreased as protein and β-casein concentration increased in cheese. β-Casein seemed to be not hydrolyzed. The rate of decrease of hardness was also slower for enriched cheeses.

Effect of high pressure processing on rennet coagulation properties of milk

The effect of high pressure (HP) treatment of milk on rennet coagulation properties were evaluated. Three coagulation parameters—lag time, mean coagulation rate and inflexion time (time for reaching the point of maximum coagulation rate) were evaluated as a function of pressure (200–400 MPa), temperature (3–21 °C) and holding time (10–110 min) using a response surface methodology. A central composite rotatable design and a second order multiple response model were used to investigate the effect of process variables (pressure, temperature and holding time) and relate them to coagulation parameters. In general, with an increase in pressure or holding time, or a decrease in temperature, lag and inflexion times associated with the rennet coagulation showed a decreasing trend while the mean coagulation rate showed the opposite. Canonical analyses indicated that the stationary point was a saddle point for lag time and mean coagulation rate whereas a minimum for inflexion time. At the stationary point, the predicted values were: lag time, 7.7 min (85 min HP treatment at 296 MPa and 5 °C); inflexion time, 11.3 min (50 min treatment at 370 MPa and 6 °C) and mean coagulation rate, 0.0034 min −1 (72 min at 275 MPa and 14 °C).

High pressure homogenisation of raw whole bovine milk (a) effects on fat globule size and other properties.

Although widely adopted by the chemical and pharmaceutical industries in recent years, little published data is available regarding possible applications of high pressure homogenisation for dairy products. The objective of this work was to compare the effects of conventional (18 MPa, two-stage) and single or two-stage high pressure homogenisation (HPH) at 50-200 MPa on some properties of raw whole bovine milk (approximately 4% fat). Fat globule size decreased as HPH pressure increased and, under certain conditions of temperature and pressure, HPH yielded significantly smaller fat globules than conventional homogenisation. Fat globule size was also affected by milk inlet temperature. The pH of all homogenised milk samples decreased during 24 h refrigerated storage. Total bacterial counts of milk were decreased significantly (P < 0.05) for milk samples HPH-treated at 150 or 200 MPa. Whiteness and rennet coagulation properties of milk were unaffected or enhanced, respectively, as homogenisation pressure was increased. Average casein micelle size decreased slightly when skim milk was homogenised at 200 MPa. Thus, HPH treatment has several, potentially significant, effects on milk properties.

Effects of Added Plasmin on the Formation and Rheological Properties of Rennet-Induced Skim Milk Gels

Elevated plasmin enzyme activity has been suggested as a likely cause of impaired functional properties that occur in milk from cows either in their latelactational period or that are experiencing mastitis. However, there are conflicting reports on the impact of plasmin on rennet coagulation properties of milk. The effects of added plasmin on the rheological properties, at small and large deformation, of rennet-induced gels were investigated. The microstructure of rennet-induced gels was studied, using confocal scanning laser microscopy. Porcine plasmin was added to reconstituted milk, and samples were incubated at 37°C for between 0.5 to 8h. The hydrolysis reaction was terminated using soybean trypsin inhibitor. The extent of degradation of caseins was determined with SDS-PAGE. The extent of breakdown of αs- and β-caseins increased with incubation time with plasmin. Storage modulus of rennet gels decreased linearly with increasing degradation of caseins. There was an increase in the loss tangent parameter of the gels with increasing casein degradation, indicating a more liquid-like gel character. Gelation time decreased until approximately 3h of incubation with plasmin (when the amounts of intact αs- and β-caseins were ∼46 and 50%, respectively); thereafter, gelation time increased considerably. Yield stress of rennet-induced gels decreased with increasing casein breakdown. When the level of casein hydrolysis was high (<40% of intact caseins), the microstructure of rennet-induced gels was drastically altered. Even when there were low levels of casein hydrolysis, the rheological properties of rennet gels were altered, which could have negative impacts on cheese yield and texture.

Effects of the CSN1A(G) allele on the clotting time of cow milk and on the rheological properties of rennet-curd.

The aim of this research was to study the effects of the CSN1A(G) allele on the main rennet coagulation properties of milk. The study was carried out on individual milk samples with low alphas1-casein obtained from 19 Italian Brown cows heterozygous for the CSN1A(G) allele (seventeen CSN1A BG and two CSN1A CG) from four herds in the province of Parma (Italy). Control cows (sixteen CSN1A BB and three CSN1A BC) giving milk with normal alphas1-casein levels were chosen from within the same herds in order to establish pairs of cows with identical environment and management conditions, and comparable lactation stages and numbers. Individual milk samples from single pairs of cows with somatic cell counts and lactose and chloride levels within the normal ranges were collected and analysed in parallel. Rennet coagulation properties of milk were analysed using Formagraph and Gel Tester. Milk from low alphas1-casein cows was characterized by lower casein content, lower titratable acidity and a higher proportion of kappa-casein in total casein. The clotting time of this milk was approximately 23% lower than that obtained with milk from normal alphas1-casein cows. Rennet curd from low alphas1-casein milk was obtained more rapidly and had a higher final firmness: curd-firming time was approximately 35% lower and curd firmness measured 30 min after rennet addition was approximately 27% higher compared with that for normal alphas1-casein milk. In addition, curd from low alphas1-casein milk had a higher resistance to compression. These results suggest that, although a role for the CSN2 locus cannot be definitely excluded, the CSN1A(G) allele can considerably affect the main rennet coagulation properties of milk.

Effects of High Pressures Combined with Moderate Temperatures on the Rennet Coagulation Properties of Milk

The effects of milk pressurization (100–400 MPa) at different temperatures (25–60°C) on the denaturation of whey proteins, rennet coagulation time, wet cheese yield and enzymatic phase of coagulation have been investigated. The results indicated that there is a synergistic effect between pressure and temperature on the biochemical properties of milk. Pressurization at 40°C delayed coagulation time and impaired gel strength, although protein and water retention in the curd were improved as compared with milk pressurized at 25°C. The use of temperatures higher than 40°C adversely affected milk coagulation. The combined application of high pressures and moderate temperatures was found to increase the extent of β-lactoglobulin denaturation over treatments at 25°C, and pressurization at 50°C induced denaturation of α-lactalbumin. Enhanced whey protein denaturation is supposed to be responsible for hindering the enzymatic hydrolysis of κ-casein, in particular that of the glycosylated forms.

The effects of composition and some processing treatments on the rennet coagulation properties of milk

The effects of various processing parameters on the rennet coagulation properties of milk were assessed. Using low amplitude oscillation rheometry, the coagulation properties were monitored by measurement of the elastic shear modulus, G', as a function of time, t, from rennet addition; Gapos; was taken as a measure of curd firmness. The Scott‐Blair time dependency model was fitted to the experimental G' It curves for the determination of the following coagulation parameters: gel time, maximum curd firming rate, the set‐to‐cut time at 20 Pa (ie, time to reach 20 Pa) and the curd firmness after a renneting time of 2400 s. The renneting properties were enhanced by increasing the levels of milk protein and fat in the ranges 0.3–7.0% (w/w) and 0.1–10% (w/w) respectively and by two stage homogenization pressure where the first stage pressure, P1, was varied from 0 to 25 MPa and the second stage pressure, P2, was held constant at 5 MP a. The influence of these parameters, within the range investigated, in complementing the gel forming properties decreased in the following order: protein &gt; fat &gt; homogenization pressure. In contrast, the coagulation properties of milk were impaired by high heat treatment, the addition of a commercial microparticulated whey protein based fat substitute and by partial replacement of protein with fat.

Rennet coagulation properties of heated milk

Heating impaired the rennet coagulation properties of milk which deteriorated further during storage, i.e. rennet hysteresis occurred. Acidification to pH values ≤ 6.2 or addition of low concentrations of CaCl2 greatly improved the rennet coagulation properties of heated milk. Acidification of heated milk to pH values &lt; 5.5 followed by neutralization to pH 6.6 to produce reformed micelles, resulted in greatly improved rennet coagulation properties except for severely heated milks (120°C for 10 min) which were not coagulable even after acidification/neutralization. Acidification of heated milk to pH values &lt; 5.5 and storage at the low pH for 24 h before neutralization resulted in a further improvement in the rennet coagulation properties. Dialysis of heated milk that had been acidified and reneutralized against an excess of normal milk resulted in a dramatic deterioration of its rennet coagulability. Reheating milk that had been heated, acidified and reneutralized resulted in little change in RCT or gel firmness. Addition of heated milk to raw milk resulted in an increase in RCT of the latter and a reduction in gel firmness.