Rennet Coagulation Properties Research Articles

Влияние обогащения молока-сырья казеинатом натрия на физико-химические показатели сыра Качотта

Milk producers increase both milk yield and cheese production efficiency by fortifying raw milk with protein concentrates, such as sodium caseinate. In this research, we added 30 g calcium chloride to 100 L milk in order to restore its salt balance after pasteurization and improve the rennet coagulation properties. The control sample of Caciotta cheese contained no sodium caseinate; Sample 1 had 10% sodium caseinate; Sample 3 included 20% sodium caseinate. The fat vs. protein ratio in all the samples remained constant throughout the study. The experimental cheeses contained less fat, more moisture, and more salt, compared to the control sample. Sodium caseinate proved able to increase the yield of the fortified finished product.

Influence of β-casein genotype on Cheddar cheese making and ripening

Milk characteristics and suitability for production of dairy products like cheese may be influenced by protein polymorphism; the possible influence of β-casein (β-CN) polymorphism on cheese manufacturing and cheese characteristics was examined using milk with three β-CN genotypes, A1A1, A1A2 and A2A2. The composition and rennet coagulation properties of raw and standardised cheese milk, cheese yield and their composition were examined, cheese meltability, texture and proteolysis were analysed at different ripening times. Milk with β-CN variant A2A2 was found to have poorer rennet coagulation properties following standardisation and pasteurisation. Cheese made from A1A1 milk had lower protein content, while that from A2A2 milk had lower fat content compared with the other two genotypes. There was no significant impact of genotype on proteolysis during cheese ripening. However, β-CN genotype was found to impact cheese texture; after 180-d ripening, the A1A1 cheese was the softest, and A2A2 cheese was the most fracturable.

Acid and Rennet Coagulation Properties of A2 Milk.

This study investigated the acid and rennet milk coagulation properties of A2 milk (β-casein (CN) A2A2 genotype), in comparison to a control milk (blend of A2A1/A1A1/A2A2 genotypes). Acid and rennet coagulation were evaluated using the Optigraph® system, measuring the coagulation time, aggregation rate, and gel density or curd firmness. The acidification kinetics were monitored using a CINAC® system, evaluating the time to reach pH 4.6, the acidification rate, the maximum acidification rate, the time required to reach it, and the latency time. The water-holding capacity of acid milk gels and the potential yield, total solids, and syneresis of enzymatic gels were also evaluated. Some variables were highly influenced by the farm factor, showing the importance of the effect of extrinsic parameters. Acid and enzymatic coagulation times were not affected in either milk. The A2 milk presented higher acid gel density and latency time than the control milk. Although the differences in water-holding capacity were not statistically significant, the A2 milk presented lower values, related with the higher gel density. The A2 milk also showed higher rennet aggregation rate and curd firmness than the control milk. Potential yield and syneresis were higher in the A2 milk, which is in accordance with the higher firmness of curd. Coagulation results and gel and curd properties indicate that it is possible to manufacture acid and rennet coagulation dairy products from A2 milk with no major differences when compared with a control milk.

Effect of konjac glucomannan and soy soluble polysaccharides on the rheological, microstructural and syneretic properties of rennet gels

This study investigated the rheological, microstructural and syneretic properties of rennet gels as influenced by the addition of soy soluble polysaccharides (2.5 g/kg, 5 g/kg) or konjac glucomannan (0.2 g/kg, 0.4 g/kg) to skim milk. The addition of all polysaccharides enhanced rennet coagulation properties, by reducing rennet coagulation time (RCT) and increasing development of gel firmness. There were also interactive effects between polysaccharide concentration and coagulation pH on parameters such as RCT, showing that the dynamics of gelation of such systems can be modulated by changing polysaccharide concentration and pH. Rennet gels containing 0.4 g/kg konjac glucomannan had significantly higher levels of syneresis (p < 0.05) than the other gels, which was linked to low yield stress and strain and a more open and porous microstructure. Quantitative analysis of 3-D confocal laser scanning microscopy image stacks showed that rennet gels containing konjac glucomannan had a significantly larger (p < 0.05) pore size than the other rennet gels. The ability of these polysaccharides to change the structure of rennet gels and their ensuing syneretic processes may provide a platform for development of novel cheese textures appealing to international consumers who may not be traditional cheese consumers.

Effect of β-casein reduction and high heat treatment of micellar casein concentrate on the rennet coagulation properties, composition and yield of Emmental cheese made therefrom

To study the effect of removing β-casein of cheesemilk on cheese manufacture, cheesemilk was formulated from low heat skim milk powder (LH CM), micellar casein concentrate with 1.83% β-casein reduction (MCC CM) and β-casein-reduced micellar casein concentrate with 4.25% β-casein reduction (LB CM) or high heat treatment (HHT; 120 °C, 15 s) LB CM to manufacture Emmental cheeses. MCC- and LB CM had similar rennet coagulation properties and similar compositions and yield in the resultant cheeses. Compared with LB CM, HHT LB CM had an increased level of denatured whey protein and a reduced, yet acceptable, curd firming rate. Higher fat losses, but lower protein losses, from cheesemilk to whey in HHT LB cheeses resulted in a similar yield compared with LB CM cheese. Overall, it was possible to remove β-casein from cheesemilk or apply high heat treatment to whey protein reduced milk without adversely affecting cheese composition and yield.

Методы оценки свертываемости белков молока в системе прогнозирования технологических свойств

Introduction. An integrated monitoring of raw milk’s contents, quality, and security is a key factor that guarantees the high-quality dairy production. As a result, new research methods of rennet clotting are a topical and urgent area of study. The research objective was to systemize and analyze the basic criteria and assessment methods of rennet-induced protein gels in milk systems. Study objects and methods. The authors reviewed the official Russian criteria and methods of raw milk assessment by its rennet coagulation properties. The research also featured the most widespread instrumental approaches used in best practices from around the world. Results and discussion. In Russian and foreign cheese production, milk is always tested for its physicochemical and microbiological indicators, with a mandatory check of its coagulation characteristics. Russian cheese-makers use different modifications of rennet and rennet-fermenting tests based on subjective sensory evaluation, while international scientific trends in this area aim at developing and improving instrumental methods by using a complex indicator MCP. This indicator characterizes the parameters of rennet coagulation with the help of such devices as Formagraph, Lattodinamografo, Optigraph, etc. Formagraph is a simple instrument for measuring rheological properties of milk clotting. It was popular in the late XX century. The resent years saw the development of other methods of instrumental control, including those based on optical measurements. For instance, Ortigraph is one such instrument that receives unified data on coagulation properties of raw milk by using near-infrared waves. Sensory and instrumental methods have their advantages and disadvantages. However, the most significant criteria for a quick test of cheeseability, yield, and quality are the speed of analysis and the comparability and reproducibility of results. Conclusion. To improve cheeseability testing, Russian cheese-makers need to use the international experience, which offers standardized evaluation criteria in combination with various instrumental approaches. However, the integration of foreign regulations and methods into Russian studies is not the only option. The improvement and development of national instrumental methods of evaluating milk protein coagulation is also crucial.

A mycotoxin-deactivating feed additive counteracts the adverse effects of regular levels of Fusarium mycotoxins in dairy cows

Little is known about the effects of commonly found levels of Fusarium mycotoxins on the performance, metabolism, and immunity of dairy cattle. We investigated the effects of regular contamination levels, meaning contamination levels that can be commonly detected in dairy feeds, of deoxynivalenol (DON) and fumonisins (FB) in total mixed ration (TMR) on the performance, diet digestibility, milk quality, and plasma liver enzymes in dairy cows. This trial examined 12 lactating Holstein dairy cows using a 3-period × 3-treatment Latin square design. The experimental period was 21 d of mycotoxin exposure followed by 14 d of washout. During treatment periods, cows received one of 3 diets: (1) CTR (control) diet of TMR contaminated with 340.5 µg of DON/kg of dry matter (DM) and 127.9 µg FB/kg of DM; (2) MTX diet of TMR contaminated with Fusarium mycotoxins at levels higher than CTR but below US and European Union guidelines (i.e., 733.0 µg of DON/kg of DM and 994.4 µg of FB/kg of DM); or (3) MDP diet, which was MTX diet supplemented with a mycotoxin deactivator product (i.e., 897.3 µg of DON/kg of DM and 1,247.1 µg of FB/kg of DM; Mycofix, 35 g/animal per day). During washout, all animals were fed the same CTR diet. Body weight, body condition score, DM intake, dietary nutrient digestibility, milk production, milk composition and rennet coagulation properties, somatic cell count, blood serum chemistry, hematology, serum immunoglobulin concentrations, and expression of multiple genes in circulating leucocytes were measured. Milk production was significantly greater in the CTR group (37.73 kg/d) than in the MTX (36.39 kg/d) and the MDP (36.55 kg/d) groups. Curd firmness and curd firming time were negatively affected by the MTX diet compared with the other 2 diets. Furthermore, DM and neutral detergent fiber digestibility were lower after the MTX diet than after the CTR diet (67.3 vs. 71.0% and 42.8 vs. 52.3%). The MDP diet had the highest digestibility coefficients for DM (72.4%) and neutral detergent fiber (53.6%) compared with the other 2 diets. The activities of plasma liver transaminases were higher after the MTX diet than after the CTR and MDP diets. Compared with the CTR diet, the MTX diet led to slightly lower expression of genes related to immune and inflammatory functions, indicating that Fusarium mycotoxins had an immunosuppressive effect. Our results indicated that feed contaminated with regular levels of Fusarium mycotoxins adversely affected the performance, milk quality, diet digestibility, metabolic variables, and immunity of dairy cows, and that supplementation with mycotoxin deactivator product counteracted most of these negative effects.

Effect of feeding hay vs. silages of various types to dairy cows on feed intake, milk composition and coagulation properties

This research paper addresses the hypotheses (1) that milk produced from hay-fed cows differs from that of silage-fed cows and (2) that silage type has an important impact, too. Four diets differing in forage type but with equal estimated milk production potential and a forage:concentrate ratio of 0.85 : 0.15 were compared regarding their effect on feed intake, milk yield and milk properties. The forages tested were hay, grass silage, conventional short-chopped and long-chopped maize silage subjected to a novel processing technology (Shredlage®). Twenty-four dairy cows were fed two of the four diets in two consecutive runs in an incomplete (4 × 2) Latin-square design (n = 12 per diet). Each experimental period lasted 22 d, with 12 d of adaptation and 10 d of sampling. During sampling, feed intake and milk yield were recorded daily, milk composition and coagulation properties were determined four times. The composition of the diet ingredients was analysed weekly. Data were analysed with a mixed model considering feed, period and their interaction as fixed effects. Stage of lactation, milk yield and milk composition from the pre-experimental period were used as covariates in the model. Dry matter intake was lower with the long-chopped processed maize silage compared to the other three groups. There were some diet differences in intakes of net energy for lactation and absorbable protein in the duodenum, but this did not result in changes in milk yield. The milk fat content was higher with the grassland-based diets compared to the maize silage diets. No treatment effect on milk acidity and rennet coagulation properties was observed. In conclusion, there were no indications for specific physico-chemical properties of milk from a hay-based diet, and maize processing technology was not of large effect either. Future investigations should focus on sensory differentiation of the milk produced with different forages.

Minor acidification of diafiltration water using various acidification agents affects the composition and rennet coagulation properties of the resulting microfiltration casein concentrate

Cheese made from microfiltration (MF) retentate may suffer from textural defects due to a high Ca concentration. The reduction of colloidal minerals by the acidification of milk before MF at pH below 6.0 has been well documented in the literature. This process, however, creates less valuable side streams to the MF process and induces changes in the casein micelles that negatively affect their coagulation properties. The objective of this study was to determine whether a minor reduction in pH by using different acidifiers in the diafiltration (DF) water could induce changes in composition and renneting properties of the MF retentate. A 2-stage filtration process was used, with the first designed to increase the casein concentration to 8% and the second to slightly reduce the casein concentrate by 0.1 pH unit by DF, without influencing the total protein concentration. Four acidifying agents were tested during DF: lactic acid, hydrochloric acid, citric acid, and carbon dioxide. Diafiltration with water was used as a reference. At the start of DF, the retentates of acid DF had a slightly reduced pH, with an average of 0.09, whereas the pH of the reference retentate increased by an average of 0.07 unit. The reference retentate regained its starting pH by the end of DF. The carbonated retentate gradually increased in pH during processing, whereas the pH of the lactic, hydrochloric, and citric acid retentates remained constant. The permeate from the lactic acid and carbonated treatments had a reduced whey protein content compared with the reference. The total P and inorganic phosphate were lowered in the retentate by using carbonation. The total amount of Mg and Na were lowered in the retentate by using citric acid. The ionic Ca content in the retentate increased with use of lactic or hydrochloric acid. The type of acidifier used reduced the rennet clotting time. Combined acidified diafiltration with a slight reduction affects the permeate composition and improves the retentate clotting time despite the minimal mineral modification.

Effect of thermoresistant protease of Pseudomonas fluorescens on rennet coagulation properties and proteolysis of milk

This study aimed to investigate the effect of different activity levels of a thermoresistant protease, produced by Pseudomonas fluorescens (ATCC 17556), on the cheesemaking properties of milk and proteolysis levels. Sterilized reconstituted skim milk powder was inoculated with the bacteria, and after incubation, centrifuged to obtain a supernatant-containing protease. Raw milk was collected and inoculated to obtain a protease activity of 0.15, 0.60, and 1.5 U/L of milk (treatments P1, P4, and P10, respectively). One sample was not inoculated (control) and noninoculated supernatant was added to a fifth sample to be used as a negative control. Samples were stored at 4°C for 72 h. After 0, 48, and 72 h, the rennet coagulation properties and proteolysis levels were assessed. The protease produced was thermoresistant, as no significant differences were observed in the activity in the pasteurized (72°C for 15 s) and nonpasteurized supernatants. The chromatograms and electrophoretograms indicated that the protease preferably hydrolyzed κ-casein and β-casein, and levels of proteolysis increased with added protease activity over storage time. The hydrolysis of αS-caseins and major whey proteins increased considerably in P10 milk samples. At 0 h, the increase in the level of protease activity decreased the rennet coagulation time (RCT, min) of the samples, possibly due to synergistic proteolysis of κ-casein into para-κ-casein. However, over prolonged storage, hydrolysis of β-casein and αS-casein increased in P4 and P10 samples. The RCT of P4 samples increased over time and the coagulum became softer, whereas P10 samples did not coagulate after 48 h of storage. In contrast, the RCT of P1 samples decreased over time and a firmer coagulum was obtained, possibly due to a lower rate of hydrolysis of β-casein and αS-casein. Increased levels of protease could result in further hydrolysis of caseins, affecting the processability of milk over storage time.

Effect of freezing temperatures and time on mineral balance, particle size, rennet and acid coagulation of casein concentrates produced by microfiltration

The effects of freezing temperature and storage time on mineral partition, particle size, and rennet and acid coagulation properties of microfiltered casein concentrates (CC) were investigated. The total inorganic phosphate content of the CC decreased (P < 0.05) in the frozen samples, while the calcium and inorganic phosphate concentrations in the serum fraction were dependent on the freezing temperature; serum levels of Ca and Pi decreased (P < 0.05) during 12 days of storage at −20 and −40 °C, but increased at −80 °C. The frozen samples formed aggregates of different mass median diameters, and the average size was dependent on the temperature and days of storage. Rennet coagulation properties were significantly altered by storing at −80 °C. The storage modulus of acid gels made from frozen CC had higher values compared with acid gels made from unfrozen CC. The process of freezing thus influenced the stability of the CC.

Natural variations of citrate and calcium in milk and their effects on milk processing properties

Natural variations among milk constituents, and their relations to each other as well as to processing parameters, represent possibilities for differentiation of milk to produce high-quality natural products. In this study, we focused on natural variations in milk citrate and its interplay with calcium distribution in milk, in relation to processing properties. Milk samples from individual cows from farms varying in feeding and management practices were collected from April to June 2017 to maximize natural variations in citrate and calcium. Chemical composition, rennet coagulation properties, and ethanol stability were analyzed for all milk samples. We focused particularly on calcium distribution and citrate content and the correlation of these to other milk parameters. No significant change in citrate content was observed during the sampling period, which suggests that mechanisms other than feeding affect citrate levels in milk. Several significant correlations were found, including a positive correlation between complexed serum calcium and citrate, and a negative correlation between urea and ionic calcium. These are both of interest in relation to further processing, as with regard to the stability of UHT milk and in cheese making. Although the correlation between complexed serum calcium and citrate may be explained by their affinity, the underlying driver for the negative relationship between natural milk urea and ionic calcium needs to be clarified by further studies. Furthermore, milk from the different farms varied not only with regard to organic versus conventional farming systems; feeding practices between farms also play an important role in milk composition and functionality. However, none of the differences in milk composition between farms were found to decrease milk functionality and thus would probably not cause any processing problems.

Improving rennet coagulation and cheesemaking properties of reverse osmosis skim milk concentrates by pH adjustment

The use of reverse osmosis (RO) for cheese milk concentration has advantages including obtaining reusable low pollutant permeates and reducing milk transportation costs. However, high levels of lactose and salts in RO concentrates impair their cheesemaking abilities. The objective of this work was to optimise the use of RO concentrates (5–11% protein content) for cheesemaking by pH adjustment. Rennet coagulation kinetics, salt partitioning and cheesemaking properties were studied in comparison with ultrafiltration concentrates. Results showed that concentration by RO induced an increase regarding the coagulation time and the gel maximal firming rate that reached a plateau at 9% protein content. Increases in calcium mineralisation of casein micelles as well as in yield, moisture and lactose content in model cheese were observed. Lowering renneting pH was found to improve the cheesemaking properties of RO concentrates by promoting partial demineralisation of casein micelles, accelerating coagulation kinetics and increasing curd drainage.

Effect of milk protein genetic polymorphisms on rennet and acid coagulation properties after standardisation of protein content

The effects of milk protein genetic polymorphisms on the rennet and acid coagulation properties of milk after protein standardisation were investigated. Skim milk samples were adjusted to a protein concentration of 6.07 ± 0.06% by ultrafiltration (UF) before evaluating rennet coagulation and acid coagulation properties. Only the β-lactoglobulin (β-LG) genotypes influenced the rennet-clotting time before standardisation for the total protein concentration by UF; however, this effect was confounded with the β-LG concentration. After UF-concentration, a similar protein concentration between the samples was achieved in the retentate, then the rennet clotting time and rennet curd firmness at 30 min were significantly influenced by both the κ-casein (κ-CN) and β-LG genotypes. κ-CN genotypes significantly influenced the acid coagulation properties of both skim milk and retentate. Variations in the concentration of milk proteins (mostly αS2-CN-12P) explained most of the differences in the rennet and acid coagulation properties of milk after protein standardisation by UF.

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.

Changes in rheological properties of Edam-type cheese during ripening

Understanding the parameters affecting the rheological characteristics of cheese enables better regulation and monitoring of cheese consistency and the production of cheese with desired quality. The objectives of this research were to define the linear viscoelastic rheological properties of large scale production Edam-type cheese, to characterize the effect of ripening (from three days to 10 weeks) and to determine the effect of cheese composition and cheese milk on the rheological properties of Edam-type cheese. Changes in the viscoelastic properties were more noticeable in the first four weeks of the ripening period and thereafter stabilized. Highest significant correlations for G’ and G’’ observed with the ratio of cheese moisture plus fat to protein. The compositional parameters of cheese related to rheological properties (moisture, moisture in the non-fat substance (MNFS) and moisture to protein ratio) significantly correlated with vat milk protein content and rennet coagulation properties.

The response of goats to different starch/NDF ratios of concentrates on the milk chemical composition, fatty acid profile, casein fractions and rennet clotting properties

The partial substitution of corn grain (rich in starch) with agro-industrial by-products (rich in NDF) could be a good strategy to reduce ruminant dietary costs with no negative effects on milk properties. Thus, the present study aimed to investigate the effect of different starch/NDF ratios of concentrates, with fixed forage proportions, on the chemical composition and fatty acid profile as well as on the relative proportions of individual caseins and rennet clotting properties of goat’s milk. For this purpose, sixteen crossbred dairy goats were divided into two homogeneous sub-groups based on their mean body weight and milk fat corrected yield. Each goat of each group was fed individually with alfalfa hay, wheat straw and concentrates. The two concentrates of the two dietary treatments were formulated to produce difference starch/NDF ratios, which were 1.2 and 0.3 for high starch (HS) and low starch (LS), respectively. The results showed no significant effect on milk chemical composition between the two dietary treatments. Moreover, the different starch/NDF ratios of the concentrates had no effect on the casein profile and coagulation properties of goat’s milk. A significant reduction of κ- and αs2- casein percentages in the milk throughout the experimental period was found. Finally, the different starch/NDF ratios of the concentrates did not reveal remarkable differences in milk fatty acids except for the individual proportions of C4:0, C6:0, C18:0 and C18:2n:6t, which were significantly higher, while those of C14:1, C15:0, C16:1, C17:0, C17:1 and C20:3n-3 were significantly lower, in goats that were milk fed with the HS diet compared with those who consumed the LS. In conclusion, the 4 times decrease in the starch/NDF ratio of the concentrates without changing the forage/concentrate ratio of the goat’s diet could reduce the feeding cost without causing any problems in the rennet clotting properties of milk and consequently in the milk industry.

Comparison of milk protein composition and rennet coagulation properties in native Swedish dairy cow breeds and high-yielding Swedish Red cows

Recent studies have reported a very high frequency of noncoagulating milk in Swedish Red cows. The underlying factors are not fully understood. In this study, we explored rennet-induced coagulation properties and relative protein profiles in milk from native Swedish Mountain and Swedish Red Polled cows and compared them with a subset of noncoagulating (NC) and well-coagulating (WC) milk samples from modern Swedish Red cows. The native breeds displayed a very low prevalence of NC milk and superior milk coagulation properties compared with Swedish Red cows. The predominant variants in both native breeds were αS1-casein (αS1-CN) B, β-CN A2 and β-lactoglobulin (β-LG) B. For κ-CN, the B variant was predominant in the Swedish Mountain cows, whereas the A variant was the most frequent in the Swedish Red Polled. The native breeds displayed similar protein composition, but varied in content of αS1-CN with 9 phosphorylated serines (9P) form. Within the Swedish Mountain cows, we observed a strong inverse correlation between the relative concentration of κ-CN and micelle size and a positive correlation between ionic calcium and gel firmness. For comparison, we investigated a subset of 29 NC and 28 WC milk samples, representing the extremes with regard to coagulation properties based on an initial screening of 395 Swedish Red cows. In Swedish Red, NC milk properties were found to be related to higher frequencies of β-CN A2, κ-CN E and A variants, as well as β-LG B, and the predominant composite genotype of β- and κ-CN in the NC group was A2A2/AA. Generally, the A2A2/AA composite genotype was related to lower relative concentrations of κ-CN isoforms and higher relative concentrations of αS1-, αS2-, and β-CN. Compared with the group of WC milk samples, NC milk contained a higher fraction of αS2-CN and α-lactalbumin (α-LA) but a lower fraction of αS1-CN 9P. In conclusion, milk from native Swedish breeds has good characteristics for cheese milk, which could be exploited in niche dairy products. In milk from Swedish Mountain cows, levels of ionic calcium seemed to be more important for rennet-induced gel firmness than variation in the relative protein profile. In Swedish Red, lower protein content as well as higher fraction of αS2-CN and lower fraction of αS1-CN 9P were related to NC milk. Further, a decrease in the frequency of the composite β-κ-CN genotype A2A2/AA through selective breeding could have a positive effect on milk coagulation properties.

Investigating rennet coagulation properties of recombined highly concentrated micellar casein concentrate and cream for use in cheese making

Highly concentrated micellar casein concentrate (HC-MCC) contains ∼18% casein with ∼70% of whey proteins removed by microfiltration and diafiltration of skim milk, followed by vacuum evaporation for further concentration. When blended with cream, HC-MCC forms recombined concentrated milk (RCM), which could be used as a starting material in cheese making. Our objective was to investigate the rennet coagulation properties of RCM while varying parameters such as casein level, pH, rennet level, and coagulation temperature. The HC-MCC was mixed with cream using low shear at 50°C for 10 min, followed by cooling to 31, 28, or 25°C and adding rennet, and rheological properties were determined. Rennet coagulation time [RCT, the time at which storage modulus (G') = loss modulus (G″)] decreased from 8.7 to 7.4 min as casein level increased from 3.2 to 5.7%, without a significant additional difference in RCT at casein levels >5.7%. The initial G″ (G″0) increased about 10-fold when casein levels were increased from 3.2 to 10.9%, whereas no change in initial G' (G'0) was observed. When G' was measured relative to RCT (i.e., 1, 1.5, or 2 times RCT after RCT was reached, and expressed as G'1, G'1.5, and G'2), log relationship was found between relative G' and casein level (R2 > 0.94). Lowering coagulation temperature from 31 to 25°C increased G″0 by 6 fold and extended RCT from 7.4 to 9.5 min. After coagulation, relative G' was initially higher at the lower temperature with G'1 of 3.6 Pa at 25°C and 2.0 Pa at 31°C, but delayed in further development with G'2 of 0.8 kPa at 25°C and 1.1 kPa at 31°C. Lowering pH of RCM from 6.6 to 6.2 resulted in reduced RCT from 11.9 to 6.5 min with increased relative G' after coagulation. When less rennet was used, RCT increased in a linear inverse relationship without changes in relative G' or G″. The microstructure of RCM coagulum (∼11% casein), observed using transmission electron microscopy, confirmed that RCM curd had a rigid protein matrix containing extensively cross-linked protein strands.

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.