Diameter Of Casein Micelles Research Articles

Rheology of buffalo milk rennet coagulation and gels affected by coagulation temperature, CaCl2, pH and milk heat treatment

The effects of coagulation temperature, CaCl2 concentrations, pH and heat treatment on the rennet coagulation time (RCT), setting time (ST), aggregation rate (AR) and gel firmness (GF) of buffalo milk were studied using dynamic small amplitude oscillatory rheology. The influence of heat treatments on protein profile and casein micelle size was analysed by PAGE electrophoresis and dynamic light scattering. Reducing pH of milk from 6.5 to 6.3 caused the largest decrease in RCT and ST, and the largest increase in AR and GF (P < 0.01) compared with the influence of other examined factors. Decreasing the coagulation temperature from 31 to 27 °C had a minor effect on the rennet coagulation parameters. The amount of CaCl2 added to milk treated with mild heat treatment had a negligible effect on the rennet coagulation parameters. High heat treatment induced an increase in casein micelle diameter and substantially delayed the process of milk coagulation.

Оценка влияния полиморфизма гена κ-казеина в сухом молоке на технологические свойства кислотно-индуцированных молочных гелей

Introduction. Yoghurt has become one of the most popular acid-induced dairy products in the world. Consumers see yoghurt not only as a tasty, protein-rich, and calcium-fortified dessert, but also as a product that improves intestinal microflora and prevents obesity, metabolic syndrome, type II diabetes, and cardiovascular diseases. The stability of the structure and consistency of yoghurt directly depend on the composition and properties of raw materials, including genetic and technological factors and compliance with temperature storage conditions. Yoghurt formulations include various dairy raw materials, e.g. milk powder. The research objective was to assess the effect of κ-casein gene polymorphism in milk powder on the technological properties of acid-induced milk gels when simulating different temperature storage conditions. Study objects and methods. The research featured yoghurt samples prepared from milk powder of CSN3 gene (AA and BB). Model systems of yoghurt were prepared from dry bulk milk, mixed by mass fraction of protein in the ratio of AA2:BB2 as 75:25, 50:50, and 25:75%, respectively. The experiment involved standard methods, optical methods, dynamic viscometry, and PCR-RFLP. Results and discussion. As the mass fraction of BB dry bulk milk increased, the structural and mechanical properties, dimensional stability, and surface tension increased, too. As the storage temperature fell from 4 ± 2 to 12 ± 2°C, the structural and mechanical properties, dimensional stability, surface tension, and moisture-holding ability decreased while maintaining the previously established dependencies. The CSN3 gene polymorphism proved to have no effect on the curd tension after fermentation. Significant differences between the allelic variants AA and BB became obvious only after complete cooling and structuring of the product. Conclusion. The obtained experimental results and the analysis of related publications suggested an indirect effect of the κ-casein gene polymorphism on the structural and mechanical properties, associated with a genetic effect on the average diameter of casein micelles in the original milk and the resulting biochemical and isothermal processes. The research made it possible to assess the effect of the CSN3 gene polymorphism on the technological properties of dry milk during its processing into fermented milk products.

Influence of Processing Temperature on Membrane Performance and Characteristics of Process Streams Generated during Ultrafiltration of Skim Milk.

The effects of processing temperature on filtration performance and characteristics of retentates and permeates produced during ultrafiltration (UF) of skim milk at 5, 20, and 50 °C were investigated. The results indicate that despite higher flux at 50 °C, UF under these conditions resulted in greater fouling and rapid flux decline in comparison with 5 and 20 °C. The average casein micelle diameter was higher in retentate produced at 5 and 20 °C. The retentate analysed at 5 °C displayed higher viscosity and shear thinning behaviour as compared to retentate analysed at 20 and 50 °C. Greater permeation of calcium and phosphorus was observed at 5 and 20 °C in comparison with 50 °C, which was attributed to the inverse relationship between temperature and solubility of colloidal calcium phosphate. Permeation of α-lactalbumin was observed at all processing temperatures, with permeation of β-lactoglobulin also evident during UF at 50 °C. All UF retentates were shown to have plasmin activity, while lower activity was measured in retentate produced at 5 °C. The findings revealed that UF processing temperature influences the physicochemical, rheological, and biochemical properties of, and thereby govern the resulting quality and functionality of, retentate- and permeate-based dairy ingredients.

Rapid removal of rhodamine dye from aqueous solution using casein-surfactant complexes: role of casein-surfactant interaction

We report here a new approach to remove rhodamine B dye, a toxic contaminant in industrial effluents, from aqueous solution using colloidal casein protein and its complexes with surfactants. The dye removal efficiency of casein is studied in the absence and in the presence of anionic, cationic, and nonionic surfactants. The anionic, cationic, and nonionic surfactants used in this study are sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and Triton X-100, respectively. The presence of Triton X-100 is found to improve the dye removal efficiency of casein from 21 to 84% with a contact time of 5 minutes. The effect of contact time, pH, and temperature on the dye removal efficiency of casein is also studied here. The adsorption of rhodamine B on casein micelles is found to follow the Freundlich adsorption isotherm and a pseudo second order kinetics model. The variation in hydrodynamic diameter of casein in whole and skimmed milk exhibited similar trend for a given surfactant at different concentrations, which suggests that the presence of fat globules, does not interfere with the interaction of casein for a given surfactant. The hydrodynamic diameter of casein micelles in reconstituted aqueous casein solution is found to increase with an increase in the concentration of SDS, which is attributed to the interaction of SDS with micelles at calcium phosphate sequestration centers, which results in micelle swelling. In the presence of CTAB at varying concentration, the diameter of casein micelles in reconstituted aqueous casein is found to decrease. This is attributed to the interaction of cationic group of CTAB with negatively charged κ-casein which makes the micelles more compact as a result of reduced electrostatic repulsion between the micelles. Similarly, the hydrodynamic diameter of casein micelles in reconstituted casein containing varying concentrations of Triton X-100 is found to decrease which suggests that large micelles break down into smaller micelles. Thus, this work gives new insights to the interaction of casein with anionic, cationic, and nonionic surfactants when present in whole milk, skimmed milk, and reconstituted aqueous solution. Further, casein-Triton X-100 complexes are found to effectively remove rhodamine B dye rapidly due to the synergistic interaction between casein, rhodamine B, and Triton X-100.

Influence of heat treatment of goat milk on casein micelle size, rheological and textural properties of acid gels and set type yoghurts.

Acid gels and yoghurts were made from goat milk that was heated at 72°C/30 s, 85°C/5 min, and 95°C/5 min, followed by acidification with starter culture at 43C until pH 4.6. The rheological and textural properties of acid gels and yoghurts were analyzed using dynamic low amplitude oscillatory rheology and back extrusion texture analysis, respectively. The effect of goat milk heat treatment on the mean casein micelle diameter and protein profile was also determined by dynamic light scattering and SDS PAGE electrophoresis, respectively. The shortest gelation and fermentation time was recorded for yoghurt prepared from milk heated at 85°C/5 min. Also, the pH of gelation, the storage moduli (G') and yield stress were higher for this yoghurt, compared with the other two. Textural properties of goat milk yoghurts such as firmness and consistency were strongly affected by milk heat treatment, and the highest values were recorded for yoghurt produced from milk preheated at 85°C/5 min, as well. The largest casein micelles were measured after 85°C/5 min treatment and their size decreased at higher temperature, despite higher denaturation of whey proteins at the most intense heat regime, indicating the structure changes that influence on the acid gelation.

Изучение структурно-механических характеристик ферментированных взбитых молочных продуктов

Introduction. Whipped dairy products can be used both as finished and semi-finished products in confectionery industry. Therefore, this sphere constantly requires new technologies. A wide range of additives, stabilizers, and structure-forming agents make it possible to get products with programmed sensory, structural, and mechanical properties. Enzymatic processing of milk base is one of the modern directions in the development of whipping process, as it requires no artificial components. Enzyme preparations of plant and microbial origin were developed to satisfy the needs of the increasing production demand and to compensate for the acute shortage of animal rennet. These enzymes have a high proteolytic activity and exhibit good technological properties in dairy industry. The research objective was to study the fermentation process with preparations of different origin and optimize the proteolysis process to obtain a milk base with a high foaming capacity and maximal stability.&#x0D; Study objects and methods. The research featured samples of fermented reduced skim milk. The following enzymes were selected for enzymatic hydrolysis: animal origin – rennet-beef enzyme SG-50 (Russia), chicken-beef enzyme KG-50 (Russia), pepsin (Russia); microbial nature – Fromase 750 (France), Pronase E (Russia); recombinant chymosin-preparation CHY-MAX M (Denmark). The fermented systems were tested for foaming ability, foam stability, relative content of free amino acids, and the diameter of casein micelles during hydrolysis by the ratio of the height of the foam column to the initial volume. The relative content of free amino acids was determined using the method of formal titration. The diameter of casein micelles during hydrolysis was determined by dynamic light scattering using a particle size analyzer in low-volume plastic cuvettes. These indicators were determined after inactivation of enzymes by pasteurization at 90–92°C for 3–5 sec.&#x0D; Results and discussion. Enzyme preparations of various natures were added to milk. The temperature and duration were measured as rational parameters of fermentation. After inactivation of the enzymes by pasteurization method, the foaming capacity, foam stability, and the relative content of free amino acids were determined every 30 minutes after application of the preparation. The greatest foaming properties (800%) were observed in the milk base fermented with the recombinant enzyme CHY-MAX M. However, the use of this preparation in commercial production was found undesirable due to the high activity of the enzyme and the resulting complexity of the control process. The lowest foaming ability was observed in the milk sample fermented with preparations of animal origin – SG-50, KG-50, and pepsin. The optimal foaming capacity and stable whipped mass were registered in the samples hydrolyzed with microbial preparations Fromase and Pronase. Under certain rational parameters, the foaming capacity of milk was 740% and 700%, respectively, while the stability was 80%.&#x0D; Conclusion. The research featured a comparative analysis of the foaming capacity and stability of reduced skim milk foam obtained using preparations of animal and microbial origin. The enzymes of the microbial group showed the best results for the enzymatic hydrolysis of proteins in reduced milk.

Seasonal variations in composition, properties, and heat-induced changes in bovine milk in a seasonal calving system

We determined seasonal variations in the composition and characteristics of bovine milk, as well as heat-induced changes in the physicochemical properties of the milk, in a typical seasonal-calving New Zealand herd over 2 full milking seasons. Fat, protein, and lactose contents varied consistently during the year in patterns similar to those of the lactation cycle. Seasonality also had significant effects on milk calcium, ionic calcium, fat globule size, buffering capacity, and ethanol stability, but not on casein micelle size. The ratio of casein to total protein did not vary significantly over the season, but late-season milk had the highest content of glycosylated κ-casein (G-κ-CN) and the lowest content of α-lactalbumin in both years. We observed significant between-year effects on protein, total calcium, ionic calcium, pH, and casein:total protein ratio, which might have resulted from different somatic cell counts in the 2 years. Compared with heating at 90°C for 6 min, UHT treatment (140°C for 5 s) induced greater dissociation of κ-casein, a similar extent of whey protein denaturation, a lower extent of whey protein-casein micelle association, and a larger increase in casein micelle size. Indeed, UHT treatment might have triggered significant dissociation of G-κ-CN, resulting in aggregation among the casein micelles and increased apparent mean casein micelle diameter. Seasonality had significant effects on the partitioning of G-κ-CN between the micelle and the serum phase, the extent of whey protein-casein micelle association under both heating conditions, and the casein micelle size of the UHT milk.

Microstructural observation of casein micelles in milk by cryo-electron microscopy of vitreous sections (CEMOVIS).

Casein micelles are present in bovine milk as colloidal particles with diameters of 20-600 nm, which are complex macromolecular assemblies composed of four distinct types of casein and colloidal calcium phosphate (CCP). Multiple structural models of casein micelles have been proposed based on their biochemical or physical properties and observed using electron microscopy. However, the CCP distribution and crosslinking structure between CCP and casein remain unclear. Therefore, the internal structure of casein micelles in raw milk was observed using cryo-electron microscopy of vitreous sections (CEMOVIS) with high precision at high resolution. The results confirmed that the average casein micelle diameter was about 140 nm, and that the CCP diameter in casein micelles was about 2-3 nm, with an average diameter of 2.3 nm. The distribution of CCP in casein micelles was not uniform, with an average interval between CCPs of about 5.4 nm. Areas containing no black particles (attributed to CCP) were present, with an average size of about 19.1 nm. Considering previous reports, these areas possibly correspond to pores or cavities filled with water. Based on differences in the density of structures in casein micelles, we estimated that some of the casein aggregates were able to connect with CCP in a string.

Physicochemical characteristics and renneting properties of camels’ milk: A comparison with goats’, ewes’ and cows’ milks

A great variability in physicochemical and microscopic characteristics of individual milk has been observed leading to the presence of differences in kinetics of the renneting reaction and in drainage ability. Furthermore, this study shows that casein concentration, total calcium content and mean diameter of casein micelles are the principal variables explaining the major part of the variation in the renneting properties. Finally, several relationships between coagulation characteristics, drainage ability and some compositional parameters of these kinds of milk were highlighted.

Effect of solvent and temperature on the size distribution of casein micelles measured by dynamic light scattering

The objectives of this study were to investigate the effect of the solvent on the accuracy of casein micelle particle size determination by dynamic light scattering (DLS) at different temperatures and to establish a clear protocol for these measurements. Dynamic light scattering analyses were performed at 6, 20, and 50°C using a 90Plus Nanoparticle Size Analyzer (Brookhaven Instruments, Holtsville, NY). Raw and pasteurized skim milk were used as sources of casein micelles. Simulated milk ultrafiltrate, ultrafiltered water, and permeate obtained by ultrafiltration of skim milk using a 10-kDa cutoff membrane were used as solvents. The pH, ionic concentration, refractive index, and viscosity of all solvents were determined. The solvents were evaluated by DLS to ensure that they did not have a significant influence on the results of the particle size measurements. Experimental protocols were developed for accurate measurement of particle sizes in all solvents and experimental conditions. All measurements had good reproducibility, with coefficients of variation below 5%. Both the solvent and the temperature had a significant effect on the measured effective diameter of the casein micelles. When ultrafiltered permeate was used as a solvent, the particle size and polydispersity of casein micelles decreased as temperature increased. The effective diameter of casein micelles from raw skim milk diluted with ultrafiltered permeate was 176.4±5.3nm at 6°C, 177.4±1.9nm at 20°C, and 137.3±2.7nm at 50°C. This trend was justified by the increased strength of hydrophobic bonds with increasing temperature. Overall, the results of this study suggest that the most suitable solvent for the DLS analyses of casein micelles was casein-depleted ultrafiltered permeate. Dilution with water led to micelle dissociation, which significantly affected the DLS measurements, especially at 6 and 20°C. Simulated milk ultrafiltrate seemed to give accurate results only at 20°C. Results obtained in simulated milk ultrafiltrate at 6°C could not be explained based on the known effects of temperature on the casein micelle, whereas at 50°C, precipitation of amorphous calcium phosphate affected the DLS measurement.

Suitability of Dahlem Cashmere goat milk towards pasteurisation, ultrapasteurisation and UHT-heating with regard to sensory properties and storage stability

Dahlem Cashmere (DC) goats’ skim and whole milk were subjected to three standard heating procedures under pilot plant conditions, using both direct (steam injection and steam infusion) and indirect (tubular heat exchanger) techniques. Heating procedures included pasteurisation (72 °C, 32 s), ultrapasteurisation (120 °C, 4 s/10 s) and ultra high temperature (UHT)-heating (140 °C, 4 s/10 s). Additionally, heating of bovine milk was carried out as a reference. The differently treated milks were analysed with regard to sensory quality (triangle test and descriptive sensory analysis), storage stability (sedimentation at 4 and 20 °C) and casein micelle diameter (dynamic light scattering). While pasteurised DC milk showed neither processing nor sensory deficiencies, ultrapasteurised and UHT-heated DC milk were perceived as slightly to clearly grainy and showed sedimentation after 21–90 days of storage, respectively. Concerning process suitability, sensory quality and storage stability, DC skim milk gave generally better results than DC whole milk, and direct heating techniques gave better results than indirect ones. The addition of 0.05% sodium phosphate notably improved process suitability, sensory quality and storage stability of ultrapasteurised and UHT-heated DC skim and whole milk.

Structural Changes of Casein Micelles in a Calcium Gradient Film

Calcium gradients are prepared by sequentially filling a micropipette with casein solutions of varying calcium concentration and spreading them on glass slides. The casein film is formed by a solution casting process, which results in a macroscopically rough surface. Microbeam grazing incidence small-angle X-ray scattering (microGISAXS) is used to investigate the lateral size distribution of three main components in casein films: casein micelles, casein mini-micelles, and micellar calcium phosphate. At length scales within the beam size the film surface is flat and detection of size distribution in a macroscopic casein gradient becomes accessible. The model used to analyze the data is based on a set of three log-normal distributed particle sizes. Increasing calcium concentration causes a decrease in casein micelle diameter while the size of casein mini-micelles increases and micellar calcium phosphate particles remain unchanged.

Impact of zeta potential and size of caseins as precursors of fouling deposit on limiting and critical fluxes in spiral ultrafiltration of modified skim milks

Caseins, the main proteins of milk, are known to be responsible of flux limitations in tangential filtration of skim milk. These proteins are well known to be versatile with the pH. Their initial form, corresponding to the so-called “native casein micelles” is due to a complex aggregation of monomers through calcium phosphate bridges that can be disrupted by small pH variations. This paper deals with the determination of both critical and limiting fluxes during ultrafiltration of natural and modified skim milks. pH ranging from 3.7 to 11.5 allowed to consider skim milk ultrafiltration (UF) for production purpose (pH 6.6–6.7) as well as acidic and alkaline concentrated effluents. The physico-chemical characteristics of caseins, as diameter and zeta potential, were measured according to the pH variations obtained by the addition of HCl and NaOH. Then, both limiting and critical fluxes variations were correlated to these characteristics. The critical and limiting fluxes varied in a quite complicated way with the pH, leading to four different regions. At acidic pH, zeta potential was null and fluxes were controlled by large particles of caseins that precipitated in the solution. Around neutral pH, the diameter of casein micelles remained constant whereas the zeta potential varied strongly. In this region the fluxes increased linearly with the zeta potential of caseins. Then at alkaline pH, the zeta potential of caseins remained constant whereas the diameter varied showing successively partial destructuration and partial “restructuration” of new types of micelles, both different from native casein micelles. In this region the fluxes varied with the rate of large micelles. Finally, retention of lactose (main neutral solute of milk) and whole proteins, mainly responsible of COD, were measured and discussed in relationship with above-mentioned parameters.

Effect of hydrolysis of casein by plasmin on the heat stability of milk

Abstract This study examined the effect of hydrolysis of casein by added plasmin (6 mg L −1 ) on the heat stability of raw, pre-heated, serum protein-free or concentrated skim milk. Plasmin activity markedly affected the heat stability–pH profile of skim milk and serum protein-free milk, apparently by altering the properties of the casein micelles. It is probable that changes in the surface charge of the micelles, as a result of the hydrolysis of caseins, contributed to this effect. Hydrolysis by plasmin reduced the zeta-potential of the casein micelles from ∼−19 to ∼−16 mV. The effect of hydrolysis of casein by plasmin on the heat stability of pre-heated milk was less pronounced, shifting the heat stability–pH profile to more alkaline values; the heat stability of concentrated milk was unaffected by plasmin. A very high (50 mg L −1 ) level of added plasmin resulted in clearing of the skim milk; the L * value decreased from ∼75 to ∼35 after 24 h incubation at 37 °C. Clearing was correlated with a change in casein micelle diameter from an initial value of ∼175 to ∼250 nm. It is suggested that plasmin-induced changes in zeta-potential may promote micellar aggregation or changes in micelle stucture.

Kappa-carrageenan interactions in systems containing casein micelles and polysaccharide stabilizers

When polysaccharide food gums are added to milk-based fluid systems, phase separation of casein micelles inevitably occurs, due to biopolymer incompatibility. κ-Carrageenan can prevent bulk phase separation, although stabilized systems are still microscopically phase-separated. The mechanism by which κ-carrageenan stabilizes casein micelles from phase separation was studied in this research. Images from field emission scanning electron microscopy suggested that κ-carrageenan adhered to the casein micelle surface. Dynamic light scattering data showed casein micelle diameter increasing linearly ( r 2=0.978) as κ-carrageenan concentration increased, within the concentration range of 0–0.03% (w/w) and 3.65% casein. Phase separation experiments in 13% milk solids-not-fat (3.65% casein) −0.14% locust bean gum mixed systems with κ-carrageenan in the coil state (60 °C), κ-carrageenan in the helical state, but with helix aggregation blocked (addition of NaI), λ-carrageenan, guar (all at 0.01–0.03%) and agarose (0.01–0.05%) were used to understand the conditions in which stabilization of phase separation occurred. Our work suggests that both κ-carrageenan adsorption to casein micelle surfaces and κ-carrageenan helix aggregation are required for it to be effective at preventing casein micelle macroscopic phase separation from polysaccharides.

Effects of carrageenan type on the behaviour of carrageenan/milk mixtures

The apparent hydrodynamic diameter of casein micelles was determined as a function of hydrocolloid concentration at 60°C and during cooling to 20°C. The systems studied contained skim milk 100-fold diluted in permeate in the presence of either lambda-, iota-, kappa-carrageenan or guar gum. These measurements show that all three forms of carrageenan adsorb onto casein micelles, whereas guar gum does not. Lambda-carrageenan (which is always in the coil conformation) adsorbs at all the temperatures studied, whereas the iota and kappa forms adsorb only at temperatures below the onset of the helix–coil transition. The results agree with the idea that adsorption of carrageenan occurs only above a certain minimum charge density. Phase diagrams were established at 60°C for the three carrageenans and the rheological behaviour was followed on cooling and at 25°C. The results suggest that the lambda-carrageenan bridges the casein micelles at low carrageenan concentrations, leading to the sedimentation of carrageenan/milk mixtures at 60°C and structure formation on cooling. At 60°C, iota- and kappa-carrageenan induce depletion flocculation of casein micelles above a critical carrageenan concentration. On cooling, systems containing iota-carrageenan clearly form a network at the helix–coil transition temperature. The network is formed by mixed carrageenan/casein micelle crosslinks. In the presence of excess carrageenan, this network is reinforced by carrageenan/carrageenan crosslinks. For the kappa-carrageenan/casein micelle mixtures the existence of mixed carrageenan/casein micelle crosslinks is less obvious but seems likely.

Effects of sheep alpha s1-casein CC, CD and DD genotypes on milk composition and cheesemaking properties.

The effects of sheep alpha s1-casein CC, CD and DD genotypes on milk composition and cheese yield were studied. Processed bulk milk was collected from three groups of 15 ewes, carrying alpha s1-casein CC, CD and DD genotypes. CC milk was higher in casein content than CD or DD milk (+3.5 and +8.6% respectively), and had a higher protein: fat ratio and a smaller casein micelle diameter. In addition, DD milk had a significantly lower alpha s1-casein content. The main differences were in curd formation: CC milk had better renneting properties. Cheesemaking trials, carried out in a pilot plant, showed that CC milk had better cheesemaking characteristics than DD milk, while CD milk was intermediate. Both 1 d old and fully ripened cheeses had different fat: dry matter ratios and alpha s1-I-casein electrophoretic mobilities: these were lower for DD cheese. As a consequence, these genotypes could be considered as markers of milk and/or cheese quality.

Characterisation of the protein composition of casein micelles after heating

Under a French dairy industry initiative, the changes of protein composition of casein micelles induced by thermal treatment of milk have been studied. To improve the choice of milk powder as raw material for the work, it was established that drying had a low impact on renneting ability (formagraph measurement), non-casein nitrogen values and casein micelle diameter. The effect of storage of powders on the bioavailability of lysyl residues was also studied by complete hydrolysis of the proteins followed by furosine and homo-arginine measurements using an amino-acid auto analyser. After this validation step, thermal treatments of milk using both a laboratory system and an industrial process have been performed. Milk was reconstituted from the powder and heated from 70 to 100°C for 1 or 4 min. Casein micelles were then isolated from whole milk by ultracentrifugation and washed three times in a simulated milk ultrafiltrate, in order to eliminate whey proteins entrapped in micellar casein pellets. Micellar diameter was investigated by photon correlation spectrophotometry (PCS). Further qualitative and semi-quantitative studies of the micellar protein composition were carried out using PAGE systems and gel scanning. PAGE systems were used under complete or partial denaturing conditions, using sodium dodecyl sulfate (SDS) as dissociating agent, with or without dl-dithiothreitol (DTT) as a strong disulfide bond reducer.

Influence of κ-Casein Genetic Variant on Rennet Gel Microstructure, Cheddar Cheesemaking Properties and Casein Micelle Size

Cheddar cheese was manufactured on three separate occasions over a two week period from milk collected from two mid-lactation, spring-calving, Holstein–Friesian herds (n=11) containing similar casein levels, having phenotype AA or BB for κ-casein genetic variant. κ-Casein variant did not significantly (P>0.05) influence the casein content or gross composition of milk. κ-Cas ein BB milk had significantly smaller average casein micelle diameter and superior rennet coagulation properties than that of the AA milk. Pilot-scale Cheddar cheesemaking studies showed that the κ-casein BB milk resulted in significantly higher fat recoveries into cheese and higher actual and moisture-adjusted cheese yields. Cheese produced from κ-casein BB variant milk had higher concen trations of fat and lower protein levels than that produced from the AA variant. κ-Casein variant had no significant effect on prote olysis or on the acceptability scores awarded to the cheeses.

Évolution des caractéristiques physico-chimiques et des paramètres de coagulation du lait de brebis collecté dans la région de Roquefort

Summary - Evolution of physico-chemical characteristics and renneting properties of ewe's milk collected in the 'Roquefort area'. In the present work, we studied the composition of ewe's milk collected in the 'Roquefort area'. Results show real evolutions of milk composition throughout the lactation period. The study of the partition of calcium and inorganic phosphorus between the aqueous and colloidal phases shows that the concentration of colloidal components decreases during the lactation period. An increase of the mean diameter of casein micelles is observed, whereas the micelle mineralization decreases. The micelle solvatation and the proportions of asl' as2' fi and K caseins show little evolutions. Variations of the coagulation parameters throughout the lactation suggest that the rennet coagulation time rises while the gel firming rate becomes slower with advancing lactation time. The curd firmness increases weakly and the whey draining capa city of the curd decreases. ewe's milk / physico-chemical characteristic / salt distribution / micelle / rennet coagulation