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α -Lactalbumin, an abundant protein present in the milk of most mammals, is associated with biological, nutritional and technological functionality. Its sequence presents N-glycosylation motifs, the occupancy of which is species-specific, ranging from no to full occupancy. Here, we investigated the N-glycosylation of bovine α-lactalbumin in colostrum and milk sampled from four individual cows, each at 9 time points starting from the day of calving up to 28.0 d post-partum. Using a glycopeptide-centric mass spectrometry-based glycoproteomics approach, we identified N-glycosylation at both Asn residues found in the canonical Asn-Xxx-Ser/Thr motif, i.e. Asn45 and Asn74 of the secreted protein. We found similar glycan profiles in all four cows, with partial site occupancies, averaging at 35% and 4% for Asn45 and Asn74, respectively. No substantial changes in occupancy occurred over lactation at either site. Fucosylation, sialylation, primarily with N-acetylneuraminic acid (Neu5Ac), and a high ratio of N,N'-diacetyllactosamine (LacdiNAc)/N-acetyllactosamine (LacNAc) motifs were characteristic features of the identified N-glycans. While no substantial changes occurred in site occupancy at either site during lactation, the glycoproteoform (i.e. glycosylated form of the protein) profile revealed dynamic changes; the maturation of the α-lactalbumin glycoproteoform repertoire from colostrum to mature milk was marked by substantial increases in neutral glycans and the number of LacNAc motifs per glycan, at the expense of LacdiNAc motifs. While the implications of α-lactalbumin N-glycosylation on functionality are still unclear, we speculate that N-glycosylation at Asn74 results in a structurally and functionally different protein, due to competition with the formation of its two intra-molecular disulphide bridges., (© The Author(s) 2024. Published by Oxford University Press.)

Making cheese from camel milk (CM) presents various challenges due to its different physicochemical properties compared with bovine milk (BM). In this study, we investigated the chemical composition, proteolysis, meltability, oiling off, texture profile, color, microstructure, and rheological properties of low-fat Cheddar cheese (LFCC) prepared from BM-CM blends. LFCC was produced from BM or BM supplemented with 15% CM (CM15) and 30% CM (CM30), and analyzed after 14, 60, 120, and 180 d of ripening at 8°C. Except for salt content, no significant differences were observed among LFCC from BM, CM15, and CM30. The addition of CM increased the meltability and oiling off in the resulting cheese throughout storage. With respect to color properties, after melting, LFCC CM30 showed lower L* values than LFCC made from BM and CM15, and a* and b* values were higher than those of BM and CM15 samples. LFCC from CM30 also exhibited lower hardness compared with the other cheeses. Moreover, LFCC made from BM showed a rough granular surface, but cheese samples made from BM-CM blends exhibited a smooth surface. The rheological parameters, including storage modulus, loss modulus, and loss tangent, varied among cheese treatments. The determined acetoin and short-chain volatile acids (C2-C6) in LFCC were affected by the use of CM, because CM15 showed significantly higher amounts than BM and CM30, respectively. The detailed interactions between BM and CM in the cheese matrix should be further investigated., (The Authors. Published by Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

When food products are often considered only as a source of individual nutrients or a collection of nutrients, this overlooks the importance of interactions between nutrients, but also interactions between nutrients and other constituents of food, i.e., the product matrix. This product matrix, which can be defined as ' The components of the product, their interactions, their structural organization within the product and the resultant physicochemical properties of the product ', plays a critical role in determining important product properties, such as product stability, sensory properties and nutritional and health outcomes. Such matrix effects can be defined as ' the functional outcome of specific component(s) as part of a specific product matrix '. In this article, dairy matrix effects are reviewed, with particular emphasis on the nutrition and health impact of dairy products. Such matrix effects are critical in explaining many effects of milk and dairy products on human nutrition and health that cannot be explained solely based on nutrient composition. Examples hereof include the low glycemic responses of milk and dairy products, the positive impact on dental health, the controlled amino acid absorption and the absence of CVD risk despite the presence of saturated fatty acids. Particularly, the changes occurring in the stomach, including, e.g., coagulation of casein micelles and creaming of aggregated fat globules, play a critical role in determining the kinetics of nutrient release and absorption.

Background : In vitro studies suggest that casein coagulation of milk is influenced by its mineral composition, and may therefore affect the dynamics of protein digestion, gastric emptying and appearance of amino acids (AA) in the blood, but this remains to be confirmed in vivo . Objective : This study aimed to compare gastrointestinal digestion between two milks with the same total calcium content but different casein mineralization (CM). Design : Fifteen males (age 30.9 ± 13.8 years, BMI 22.5 ± 2.2 kg m -2 ) participated in this randomized cross-over study with two treatments. Participants underwent gastric magnetic resonance imaging (MRI) scans at the baseline and every 10 min up to 90 min after consumption of 600 ml milk with low or high CM. Blood samples were taken at the baseline and up to 5 hours postprandially. Primary outcomes were postprandial plasma AA concentrations and gastric emptying rate. Secondary outcomes were postprandial glucose and insulin levels, gastric coagulation as estimated by image texture metrics, and appetite ratings. Results : Gastric content volume over time was similar for both treatments. However, gastric content image analysis suggested that the liquid fraction emptied quicker in the high CM milk, while the coagulum emptied slower. Relative to high CM, low CM showed earlier appearance of AAs that are more dominant in casein, such as proline (MD 4.18 μmol L -1 , 95% CI [2.38-5.98], p < 0.001), while there was no difference in appearance of AAs that are more dominant in whey protein, such as leucine. The image texture metrics homogeneity and busyness differed significantly between treatments (MD 0.007, 95% CI [0.001, 0.012], p = 0.022; MD 0.005, 95% CI [0.001, 0.010], p = 0.012) likely because of a reduced coagulation in the low CM milk. Conclusions : Mineral composition of milk can influence postprandial serum AA kinetics, likely due to differences in coagulation dynamics. The clinical trial registry number is NL8959 (https://clinicaltrials.gov).

The manufacture of camel milk (CM) yogurt has been associated with several challenges, such as the weak structure and watery texture, thereby decreasing its acceptability. Therefore, this study aimed to investigate the effect of whey protein isolate (WPI) addition on the health-promoting benefits, texture profile, and rheological properties of CM yogurt after 1 and 15 d of storage. Yogurt was prepared from CM supplemented with 0, 3, and 5% of WPI and compared with bovine milk yogurt. The results show that the water holding capacity was affected by WPI addition representing 31.3%, 56.8%, 64.7%, and 45.1% for yogurt from CM containing 0, 3 or 5% WPI, and bovine milk yogurt, respectively, after 15 d. The addition of WPI increased yogurt hardness, adhesiveness, and decreased the resilience. CM yogurt without WPI showed lower apparent viscosity, storage modulus, and loss modulus values compared with other samples. The supplementation of CM with WPI improved the rheological properties of the obtained yogurt. Furthermore, the antioxidant activities of yogurt before and after in vitro digestion varied among yogurt treatments, which significantly increased after digestion except the superoxide anion scavenging and lipid oxidation inhibition. After in vitro digestion at d 1, the superoxide anion scavenging of the 4 yogurt treatments respectively decreased from 83.7%, 83.0%, 79.1%, and 87.4% to 36.7%, 38.3%, 44.6%, and 41.3%. The inhibition of α-amylase and α-glucosidase, angiotensin-converting enzyme inhibition, cholesterol removal, and degree of hydrolysis exhibited different values before and after in vitro digestion., (© 2023, The Authors. Published by Elsevier Inc. and Fass Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

The ability of milk and concentrated milk to withstand a defined heat treatment without noticeable changes such as flocculation of protein is commonly denoted as heat stability. A heat treatment that exceeds the heat stability limit of milk or concentrated milk, which has a much lower heat stability, may result in undesired changes, such as separation of milk fat, grittiness, sediment formation, and phase separation. Most laboratory-scale batch heating methods were developed in the early 20th century to simulate commercial sterilization, and these methods have since been standardized. Heat stability studies have been motivated by different objectives during that time, addressing different processing issues and targets in the framework of available technology, legislation, and consumer demand. Although milk hygiene has improved during the last couple of decades, rendering milk less sensitive to coagulation, different standard methods suffered from poor comparability of results, even when comparing results for the same milk sample, indicating that unknown procedural steps affect heat stability. The prediction of heat stability of concentrated milk from the heat stability results of the corresponding unconcentrated milk for rapid quality testing purposes has been difficult, mainly due to different experimental conditions. The objective of this study is to review literature on heat stability, starting from studies in the early 20th century, to summarize the vast number of studies on compositional aspects of milk affecting heat stability, and to lead the way to the most recent work related to compositional changes in concentrates produced by membrane concentration and fractionation, respectively. Particular attention is paid to early and most recent developments and findings, such as the application of kinetic models to predict and limit protein aggregation to assess and describe heat stability as a temperature-time-total milk solids continuum., (Copyright © 2020 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The white appearance of skim milk is due to strong light scattering by colloidal particles called casein micelles. Bovine casein micelles comprise expressed proteins from four casein genes together with significant fractions of the total calcium, inorganic phosphate, magnesium and citrate ions in the milk. Thus, the milk salts are partitioned between the casein micelles, where they are mostly in the form of nanoclusters of an amorphous calcium phosphate sequestered by caseins through their phosphorylated residues, with the remainder in the continuous phase. Previously, a salt partition calculation was made assuming that the nanoclusters are sequestered only by short, highly phosphorylated casein sequences, sometimes called phosphate centres. Three of the four caseins have a proportion of their phosphorylated residues in either one or two phosphate centres and these were proposed to react with the nanoclusters equally and independently. An improved model of the partition of caseins and salts in milk is described in which all the phosphorylated residues in competent caseins act together to bind to and sequester the nanoclusters. The new model has been applied to results from a recent study of variation in salt and casein composition in the milk of individual cows. Compared to the previous model, it provides better agreement with experiment of the partition of caseins between free and bound states and equally good results for the partition of milk salts. In addition, new calculations are presented for the charge on individual caseins in their bound and free states.

Lactic acid bacteria are widely used for the fermentation of dairy products. While bacterial acidification rates, proteolytic activity and the production of exopolysaccharides are known to influence textural properties of fermented milk products, little is known about the role of the microbial surface on microbe-matrix interactions in dairy products. To investigate how alterations of the bacterial cell surface affect fermented milk properties, 25 isogenic Lactococcus lactis strains that differed with respect to surface charge, hydrophobicity, cell chaining, cell-clumping, attachment to milk proteins, pili expression and EPS production were used to produce fermented milk. We show that overexpression of pili increases surface hydrophobicity of various strains from 3-19% to 94-99%. A profound effect of different cell surface properties was an altered spatial distribution of the cells in the fermented product. Aggregated cells tightly fill the cavities of the protein matrix, while chaining cells seem to be localized randomly. A positive correlation was found between pili overexpression and viscosity and gel hardness of fermented milk. Gel hardness also positively correlated with clumping of cells in the fermented milk. Viscosity of fermented milk was also higher when it was produced with cells with a chaining phenotype or with cells that overexpress exopolysaccharides. Our results show that alteration of cell surface morphology affects textural parameters of fermented milk and cell localization in the product. This is indicative of a cell surface-dependent potential of bacterial cells as structure elements in fermented foods., (© 2018 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.)

Lactose is the main carbohydrate in the milk of most species. It is present in virtually all dry dairy ingredients, with levels ranging from <2% (e.g., caseinates, milk protein isolates) to 100% in lactose powders. The presence of lactose has a strong effect on ingredient processing and stability. Lactose can negatively influence powder properties and lead to undesirable effects, such as the stickiness of powder resulting in fouling during drying, or caking and related phenomena during storage. In addition, being a reducing carbohydrate, lactose can also participate in the Maillard reaction with free amino groups of proteins, peptides, and free AA. In this review, the influence of the presence (or absence) of lactose on physiochemical properties of dairy ingredients is reviewed, with particular emphasis on behavior during processing and storage. Particularly important features in this respect are whether lactose is in the (glassy) amorphous phase or in the crystalline phase, which is strongly affected by precrystallization conditions (e.g., in lactose, permeate, and whey powders) and by drying conditions. Furthermore, the moisture content and water activity of the ingredients are important parameters to consider, as they determine both mobility and reactivity, influencing Maillard reactions and concomitant browning, the crystallization of amorphous lactose during storage of dairy ingredients, glass transitions temperatures, and associated stickiness and caking phenomena. For the stickiness and caking, a crucial aspect to take into account is powder particle surface composition in relation to the bulk powder. Lactose is typically underrepresented at the powder surface, as a result of which deviations between observed lactose-induced caking and stickiness temperatures, and determined glass transition temperatures arise. By considering lactose as an integral part of ingredient composition along with all other compositional and environmental properties, lactose behavior in dairy ingredients can be understood, controlled, and optimized. Routes to achieve this are outlined in this review paper., (Copyright © 2016 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The susceptibility of total casein and the individual caseins in reconstituted skim milk to transglutaminase (TGase)-induced cross-linking was studied as a function of incubation temperature (5-40 °C), pH (5·0-7·0) and mineral addition. Within the ranges studied, the level of total casein cross-linked increased with increasing temperature, pH and concentration of added trisodium citrate, whereas adding calcium chloride had the opposite effect. These effects can be largely related to the effects of these parameters on TGase activity. In addition, the parameters were also found to influence the susceptibility of κ-casein, and to a lesser extent β-casein, to cross-linking, whereas the susceptibility of αs1-casein was not affected. The susceptibility of κ-casein to cross-linking increased with increasing temperature and calcium chloride addition, but decreased with increasing pH and citrate content, whereas the susceptibility of β-casein to TGase-induced cross-linking decreased with increasing temperature, but was not affected by other parameters. These findings highlight the fact that selection of environmental conditions during cross-linking can be applied to tailor the surface, and hence possibly colloidal stability, of casein micelles in TGase-treated milk.

The size distribution and protein composition of casein micelles in the milk of Holstein-Friesian cows was determined as a function of stage and number of lactations. Protein composition did not vary significantly between the milks of different cows or as a function of lactation stage. Differences in the size and polydispersity of the casein micelles were observed between the milks of different cows, but not as a function of stage of milking or stage of lactation and not even over successive lactations periods. Modal radii varied from 55 to 70 nm, whereas hydrodynamic radii at a scattering angle of 73° (Q² = 350 μm⁻²) varied from 77 to 115 nm and polydispersity varied from 0.27 to 0.41, in a log-normal distribution. Casein micelle size in the milks of individual cows was not correlated with age, milk production, or lactation stage of the cows or fat or protein content of the milk.

Milk for cheese production in Ireland is predominantly produced by pasture-fed spring-calving herds. Consequently, there are marked seasonal changes in milk composition, which arise from the interactive lactational, dietary and environmental factors. In this study, Cheddar cheese was manufactured on a laboratory scale from milk taken from a spring calving herd, over a 9-month lactation cycle between early April and early December. Plasmin activity of 6-months-old Cheddar cheese samples generally decreased over ripening time. One-dimensional urea-polyacrylamide gel electrophoresis (PAGE) of cheese samples taken after 6 months of ripening showed an extensive hydrolysis of caseins, with the fastest hydrolysis of α(s1)-caseins in cheeses made in August. A proteomic comparison between cheeses produced from milk taken in April, August and December showed a reduction in levels of β-casein and appearance of additional products, corresponding to low molecular weight hydrolysis products of the caseins. This study has demonstrated that a seasonal milk supply causes compositional differences in Cheddar cheese, and that proteomic tools are helpful in understanding the impact of those differences.

In this study, factors influencing the disruption and aggregation of casein micelles during high-pressure (HP) treatment at 250 MPa for 40 min were studied in situ in serum protein-free casein micelle suspensions. In control milk, light transmission increased with treatment time for approximately 15 min, after which a progressive partial reversal of the HP-induced increase in light transmission occurred, indicating initial HP-induced disruption of casein micelles, followed by reformation of casein aggregates from micellar fragments. The extent of HP-induced micellar disruption was negatively correlated with the concentration of casein micelles, milk pH, and levels of added ethanol, calcium chloride, or sodium chloride and positively correlated with the level of added sodium phosphate. The reformation of casein aggregates during prolonged HP treatment did not occur when HP-induced disruption of casein micelles was limited (<60%) or very extensive (>95%) and was promoted by a low initial milk pH or added sodium phosphate, sodium chloride, or ethanol. On the basis of these findings, a mechanism for HP-induced disruption of casein micelles and subsequent aggregation of micellar fragments is proposed, in which the main element appears to be HP-induced solubilization of micellar calcium phosphate.

The influence of ethanol on the rennet-induced coagulation of milk was studied to investigate potential synergistic effects of these two mechanisms of destabilisation on the casein micelles. Addition of 5% (v/v) ethanol reduced the rennet coagulation time (RCT) of milk, whereas higher levels of ethanol (10-20%, v/v) progressively increased RCT. The temperature at which milk was coagulable by rennet decreased with increasing ethanol content of the milk. The primary stage of rennet coagulation, i.e., the enzymatic hydrolysis of kappa-casein, was progressively slowed with increasing ethanol content (5-20%, v/v), possibly due to ethanol-induced conformational changes in the enzyme molecule. The secondary stage of rennet coagulation, i.e., the aggregation of kappa-casein-depleted micelles, was enhanced in the presence of 5-15% ethanol, the effect being largest at 5% ethanol. Enhanced aggregation of micelles is probably due to an ethanol-induced decrease in inter-micellar steric repulsion. These results indicate an interrelationship between the effects of ethanol and chymosin on the casein micelles in milk, which may have interesting implications for properties of dairy products.

In this study, effects of high pressure (HP) on some constituents and properties of buffalo milk were examined. HP treatment at 100-600MPa for 30 min affected casein micelle size only slightly, whereas treatment at 800 MPa increased it by approximately 35%. Levels of non-micellar alpha(S1)and beta-caseins were increased by treatment > or = 250MPa, and were highest after treatment at 400-800MPa. The level of non-micellar calcium increased with increasing pressure up to 600 MPa. The L*-value of the milk decreased gradually with increasing pressure, from approximately 82 for untreated milk to approximately 65 for milk treated at 800 MPa. Milk pH was increased by approximately 0.07 units after treatment at 100-800 MPa, with no significant difference between treatment pressures. Denaturation of alpha-lactalbumin occurred at pressures > or = 400 MPa, and reached >90% after treatment at 800 MPa, whereas beta-lactoglobulin (beta-Ig) was denatured > 100 MPa, reaching approximately 100% after treatment at 400MPa; after treatment > or = 400MPa, all beta-Ig was associated with the casein micelles. The rennet coagulation time of buffalo milk increased with increasing pressure, whereas the strength of the coagulum formed decreased after treatment at 250-800 MPa. Overall, HP treatment affected many constituents and properties of buffalo milk; some of these effects have also been observed in the milk from other species, but the extent of the effects, and the pressure at which they occurred, differed considerably.

In this study, high pressure (HP)-induced denaturation of alpha-lactalbumin (alpha-la) and beta-lactoglobulin (beta-lg) in dairy systems was examined. In both milk and whey, beta-lg was less baroresistant than alpha-la; both proteins were considerably more resistant to HP-induced denaturation in whey than in milk. HP-induced denaturation of alpha-la and beta-lg increased with increasing proportion of milk in mixtures of milk and whey. Addition of a sulphydryl-oxidising agent, KlO3, to milk or whey increased HP-induced denaturation of beta-lg, but reduced the denaturation of alpha-la. Denaturation of both alpha-la and beta-lg was prevented by adding a sulphydryl-blocking agent, N-ethylmaleimide, to milk or whey prior to HP treatment, highlighting the crucial role of sulphydryl-disulphide interchange reactions in HP-induced denaturation of alpha-la and beta-lg. Removal of colloidal calcium phosphate from milk also reduced HP-induced denaturation of alpha-la and beta-lg significantly. The higher level of HP-induced denaturation of alpha-la and beta-lg in milk than in whey may be the result of the abscence of the casein micelles and colloidal calcium phosphate from whey, which facilitate HP-induced denaturation of alpha-la and beta-lg in milk.

Effects of high pressure (HP) on average casein micelle size and denaturation of alpha-lactalbumin (alpha-la) and beta-lactoglobulin (beta-lg) in raw skim bovine milk were studied over a range of conditions. Micelle size was not influenced by treatment at pressures <200 MPa, but treatment at 250 MPa increased micelle size by approximately 25%, while treatment at > or = 300 MPa irreversibly reduced it to approximately 50% of that in untreated milk. The increase in micelle size after treatment at 250 MPa was greater with increasing treatment time and temperature and milk pH. Treatment times > or = 2 min at 400 MPa resulted in similar levels of micelle disruption, but increasing milk pH to 7.0 partially stabilised micelles against HP-induced disruption. Denaturation of alpha-la did not occur < or = 400 MPa, whereas beta-lg was denatured at pressures >100 MPa. Denaturation of alpha-la and beta-lg increased with increasing pressure, treatment time and temperature and milk pH. The majority of denatured beta-lg was apparently associated with casein micelles. These effects of HP on casein micelles and whey proteins in milk may have significant implications for properties of products made from HP-treated milk.

Heat-induced interactions of calcium and protein in milk lead to undesirable changes in the milk, such as protein coagulation, which can be minimized through the addition of calcium-sequestering salts prior to heat treatment. Thus, the present study investigated the influence of 5 mM added trisodium citrate (TSC) or disodium hydrogen phosphate (DSHP) on the heat-induced (85 °C and 95 °C for 5 min) changes in physical, chemical, and structural properties of buffalo and bovine skim milk mixtures (0:100, 25:75, 50:50, 75:25, and 100:0). Significant changes in pH and calcium activity as a result of TSC or DSHP addition subsequently resulted in higher particle size and viscosity as well as non-sedimentable protein level. These changes are mostly observed during heat treatment at 95 °C and increased proportionally to the concentration of buffalo skim milk in the milk mixture. Significant changes were affected by TSC addition in the 75:25 buffalo:bovine milk blend and buffalo skim milk, but for other milk samples, TSC addition effected comparable changes with DSHP addition. Overall, the addition of TSC or DSHP before heat treatment of buffalo:bovine milk blends caused changes in milk properties that could reduce susceptibility of milk to coagulation. [ABSTRACT FROM AUTHOR]

The consumption of food items containing digestible carbohydrates in food products leads to postprandial increases in blood glucose levels and glycemic responses. The extent to which these occur depends on many factors, including concentration and type of carbohydrate, but also other physicochemical properties of the food matrix, which determine the rate of uptake of monosaccharides into the bloodstream, including product structure and factors affecting gastric emptying. For milk, control of postprandial glycemic responses appears to be multifaceted, including a controlled rate of gastric emptying, a rate of glucose and galactose uptake into the bloodstream controlled by enzymatic hydrolysis, as well as stimulated insulin secretion to enhance uptake of blood glucose from the bloodstream. Altogether, this allows milk to deliver comparatively high levels of carbohydrate with limited glycemic responses. For plant-based drinks positioned as milk alternatives, however, compositional differences (including carbohydrate type and concentration) as well as matrix factors limiting control over gastric emptying and insulin secretion can, in some cases, lead to much stronger glycemic responses, which are undesirable in relation to non-communicable diseases, such as type-2 diabetes. This review discusses glycemic responses to milk and plant-based drinks from this perspective, focusing on mechanistic insights and food matrix effects. [ABSTRACT FROM AUTHOR]

We monitored longitudinal changes in bovine milk IgG in samples from four cows at 9 time points in between 0.5 and 28 days following calving. We used peptide-centric LC–MS/MS on proteolytic digests of whole bovine milk, resulting in the combined identification of 212 individual bovine milk protein sequences, with IgG making up >50 percent of the protein content of every 0.5 d colostrum sample, which reduced to ≤3 percent in mature milk. In parallel, we analyzed IgG captured from the bovine milk samples to characterize its N- glycosylation, using dedicated methods for bottom-up glycoproteomics employing product ion-triggered hybrid fragmentation; data are available via ProteomeXchange with identifier PXD037755. The bovine milk IgG N- glycosylation profile was revealed to be very heterogeneous, consisting of >40 glycoforms. Furthermore, these N- glycosylation profiles changed substantially over the period of lactation, but consistently across the four individual cows. We identified NeuAc sialylation as the key abundant characteristic of bovine colostrum IgG, significantly decreasing in the first days of lactation, and barely detectable in mature bovine milk IgG. We also report, for the first time to our knowledge, the identification of subtype IgG3 in bovine milk, alongside the better-documented IgG1 and IgG2. The detailed molecular characteristics we describe of the bovine milk IgG, and their dynamic changes during lactation, are important not only for the fundamental understanding of the calf's immune development, but also for understanding bovine milk and its bioactive components in the context of human nutrition. [ABSTRACT FROM AUTHOR]

The influence of ethanol (0–10%, v/v) on the acid-induced flocculation of casein micelles was examined using diffusing wave spectroscopy. For this purpose, samples containing 10% (w/w) reconstituted skim milk powder and 0–10% (v/v) ethanol were acidified with glucono-delta-lactone and acid-induced coagulation was monitored by diffusing wave spectroscopy. The pH at which acid-induced flocculation of the casein micelles commenced (pHf) increased near-linearly with increasing ethanol content, whereas the rate of flocculation was not affected by ethanol. The results are discussed in terms of the steric stabilisation of casein micelles by a polyelectrolyte brush in a medium of high ionic strength. Ethanol-induced increases in pHf are probably primarily due to an ethanol-induced reduction in solvent quality; an ethanol-induced reduction in dissociation of carboxylic acid groups in the brush is likely to contribute. [ABSTRACT FROM AUTHOR]

The influence of adding 5 m m trisodium citrate (TSC) or disodium hydrogen phosphate (DSHP) and heat treatment (85 °C or 95 °C for 5 min) on the acid gelation properties of blends of skim buffalo and bovine milk (0:100, 25:75, 50:50, 75:25, 100:0) was investigated. Significant increases in gelation pH, final G′ values, firmness, and water-holding capacity of gels were observed with increasing proportion of buffalo skim milk and with higher heating temperature. Differences in gel firmness were linked to gel microstructure, where milk blends containing higher proportion of buffalo skim milk formed gels with denser protein network clusters. The addition of TSC or DSHP reduced the gelation pH, final G′ values and gel firmness, but increased gel water-holding capacity. These results provide a better understanding of acid gelation of buffalo and bovine milk blends which will subsequently promote the potential of using milk mixtures in modulating the gel texture. [ABSTRACT FROM AUTHOR]

This study investigated the physical, chemical, and structural changes in mixtures of buffalo and bovine milk (0:100, 25:75, 50:50, 75:25, 100:0) induced by heating at 80, 85, 90, and 95 °C for 5 min. No significant changes in particle size, zeta potential, and calcium activity were observed in heated buffalo milk and its mixtures with bovine milk, irrespective of the heating temperature, but heating at ≥ 85 °C induced a significant decrease in pH. The increase in viscosity with heating was dependent on the ratio of buffalo to bovine milk and the heating temperature. The variation in casein dissociation, whey proteins denaturation and their association with themselves and casein micelles, and the alteration in salt balance were key factors that contribute to significant heat-induced changes in pH and viscosity of milk blends. [ABSTRACT FROM AUTHOR]

Although milk salts are classified as micronutrients, they strongly affect the behaviour of the proteins and the physical stability of milk and dairy products. This review focuses on heat-induced changes in milk salts, with particular emphasis on salt speciation, precipitation and association with proteins. In milk and other dairy liquids at neutral pH, heating results in precipitation of calcium phosphates. These precipitates may become stabilised by caseins and casein-derived (SerP-containing) peptides, with limited observable instability; in the absence of stabilising protein, precipitates can lead to notable instability. Increasing temperature reduces solubility of calcium phosphate, but, perhaps more importantly, also accelerates precipitate formation. In milk, heat-induced changes in salts are reversible, but only slowly, if heat-treatment is of moderate intensity. After treatment at temperatures >90 °C and/or for >20 min reversal may be incomplete. Heat-induced changes in milk salts are crucial for retaining functionality and stability during and after heating of milk. [ABSTRACT FROM AUTHOR]

Milk foams can be either desirable, e.g. for cappuccino-style beverages, or undesirable, e.g. in the reconstitution of milk powders or infant formula. In this article, compositional and processing factors affecting the foaming properties of milk are reviewed. Skim milk foams can be extremely stable, particularly when they are formed at ∼40-50°C. The presence of lipids can be detrimental to the formation and stability of milk foams, particularly at a temperature where the milk fat is partially crystalline, e.g. 20°C. The presence of phospholipids, free fatty acids and partial glycerides strongly impairs foaming of milk. [ABSTRACT FROM AUTHOR]

Abstract: Chocolate milk with different carrageenans (κappa and lambda) and sugar concentrations was heat treated indirectly at 145°C for 6s using a bench-top UHT plant. The temperature of the milk in the preheating and sterilizer sections, and the milk flow rate were determined to evaluate the overall heat transfer coefficient (OHTC) for monitoring fouling during UHT processing. Kappa-carrageenan was more effective than lambda-carrageenan in providing stability against fouling during UHT processing. By optimizing concentrations of κ-carrageenan and sugar, fouling could be minimized during UHT processing. The apparent viscosity and sedimentation of UHT-processed chocolate milk increased with increasing concentration of carrageenan and sugar. [Copyright &y& Elsevier]

Factors affecting the cross-linking of milk proteins by transglutaminase (TGase) were studied. Cross-linking of caseins in bovine skim milk was optimal over a very wide pH range. The role of micellar calcium phosphate (MCP) in maintaining the integrity of TGase-treated casein micelles was studied by incubating skim milk with 0.01% (w/v) TGase at 30°C for 1–24 h, followed by removal of MCP from untreated or TGase-treated milk by acidification and dialysis. The protein content and profile of the samples were determined by Kjeldahl and SDS-PAGE, respectively. Whey proteins in unheated milk were not susceptible to TGase-induced cross-linking. The higher level of sedimentable protein in MCP-free TGase-treated milk than in MCP-free control milk indicated that TGase treatment partially prevented disintegration of the micelle on removal of MCP, probably due to extensive intramicellar TGase-induced cross-linking of casein molecules which led to the formation of sedimentable covalently bonded casein aggregates. [ABSTRACT FROM AUTHOR]

The influence of added calcium chloride (1–10 mmol/L) on the heat-induced coagulation of skim bovine milk was examined. Unconcentrated milk displayed a pH-heat coagulation time (HCT) profile with a maximum at pH 6.6 and minimum at pH 7.0. Adding calcium chloride to unconcentrated milk progressively reduced the HCT at the maximum, increased the pH at which the maximum occurred and reduced the HCT at pH > 7.0. For concentrated milk, the shape of the pH-HCT profile, that is, a maximum at pH 6.6, was not altered by added calcium chloride, but HCT was reduced progressively with increasing concentration of calcium chloride. Preheating (90°C for 10 min) shifted the maximum in the pH-HCT profile of unconcentrated milk to a more acidic pH, and addition of 5 mmol/L calcium chloride to preheated milk induced changes in heat stability similar to those noted for unheated milk. Addition of calcium chloride to milk prior to preheating strongly reduced the stability of milk against heat-induced coagulation. These data suggest that calcium has a strong destabilizing effect on the stability of milk systems against heat-induced coagulation. [ABSTRACT FROM AUTHOR]

High pressure (HP) treatment of a casein micelle suspension at 250 and 300 MPa leads to an initial rapid increase of its light transmission, as measured in situ , indicating micellar disruption. Subsequently, a much slower, partial reversal of the HP-induced increase in light transmission is observed, indicating re-association of micellar fragments. Partial internal cross-linking of the casein micelles by the enzyme transglutaminase prior to pressure treatment slows down both the disruption and the reassociation process considerably. It is proposed that covalent cross-linking provides the micelle with extra stability against pressure-induced disruption and also prevents a molecular reorganization process required to induce reassociation of micellar fragments during prolonged pressure treatment. [ABSTRACT FROM AUTHOR]

Abstract: The influence of transglutaminase (TGase)-induced cross-linking on the ethanol stability of skimmed milk was investigated. The stability of milk against ethanol-induced coagulation increased in sigmoidal fashion with milk pH (5.0–7.5) for all samples; ethanol stability also increased upon incubation (0–24h) with 0.05gL−1 TGase at 30°C. In untreated milk, addition of ethanol induced a collapse of the polyelectrolyte brush of κ-casein on the micelle surface, thereby facilitating micellar aggregation. Dynamic and static light scattering measurements indicated that in TGase-treated milk, the ethanol-induced collapse of the polyelectrolyte brush was far less than in untreated milk, suggesting that the increased ethanol stability of TGase-treated casein micelles is caused by the cross-linking of the polyelectrolyte brush on the micellar surface. [Copyright &y& Elsevier]

Abstract: The baroprotective effect of milk constituents on Listeria innocua 4202 treated at 350 or 500MPa for 5min was examined. High-pressure (HP) treatment of L. innocua 4202 (1×109 cfumL−1) resulted in complete inactivation in simulated milk ultra-filtrate (SMUF), a ∼5.0log reduction in phosphate-buffered saline and a ∼2.9log reduction in milk. The addition of micellar casein to SMUF increased survival of the bacterium by 3logs, compared with SMUF alone, but the protective effect was negated if the minerals associated with the casein micelles were removed. The colloidal minerals calcium (30mm), magnesium (5mm), citrate (10mm) and phosphate (20mm), suspended in SMUF increased survival by ∼3.3, ∼1.7, ∼3.3 and ∼3.5logs, respectively. The buffering capacity of the suspending medium was found to be a key factor in microbial baroresistance. Buffering by phosphate and citrate in milk may protect microorganisms against changes in pH during HP treatment, whereas the divalent cations calcium and magnesium may protect cell membranes against HP. [Copyright &y& Elsevier]

Abstract: A method for the large-scale isolation of β-casein from renneted skim milk was developed. The curd from renneted skim milk was dispersed in hot (⩾70°C) water to inactivate residual chymosin. The heated curd was subsequently recovered by centrifugation, resuspended in water and incubated at 5°C, during which β-casein dissociated from the curd; the suspension was centrifuged and the aqueous phase lyophilised. The isolated protein consisted mainly of β-casein, containing a minor amount of γ-caseins and traces of other caseins. Unless chymosin was fully inactivated by heating, some β-casein was hydrolysed at the Leu192–Tyr193 bond. The yield of β-casein increased with incubation time, up to ∼20% of the β-casein present in the milk after 24h at 5°C. Reducing milk pH to 5.5 or 6.0, prior to renneting, caused a high level of contamination with αs-caseins. This isolation procedure can be easily scaled-up to an industrial process and the β-casein-depleted curd may be used for the manufacture of rennet casein or processed cheese. [Copyright &y& Elsevier]

Abstract: The influence of added NaCl (75–850mmolL−1) on some physicochemical properties of 2× or 3× concentrated milk (18 or 27%, w/v, total solids, respectively) was investigated. Adding NaCl did not influence average casein micelle size, but reduced the net-negative charge on the casein micelles and milk pH. The level of soluble and ionic calcium was increased by addition of NaCl, but the level of soluble inorganic phosphorus was not influenced. Addition of NaCl shifted the maximum in the pH–heat coagulation time (HCT) profile of 2× or 3× concentrated milk to a higher pH value and certain concentrations increased the maximum HCT, probably due to the fact that NaCl reduced the extent of heat-induced dissociation of κ-casein. Added NaCl reduced the ethanol stability, with the extent of this effect increasing with the concentration of NaCl. The key-mechanism though which added NaCl induces changes in the physico-chemical stability of casein micelles appears to be through changes in the charge on the casein micelles. [Copyright &y& Elsevier]

Abstract: Adding bovine or ovine blood serum (0.5–2.0%, v/v) to bovine milk did not affect the hydrolysis of caseins by plasmin, but equine, and particularly porcine, serum strongly inhibited casein hydrolysis; in milk containing 1.0–2.0% porcine serum, caseins were not hydrolysed by plasmin on incubation at 37°C for 7d. Porcine, and particularly equine, serum also impaired the coagulation of milk by chymosin or pepsin; equine serum (2.0%) increased the chymosin-induced coagulation time of milk ∼4-fold and a firm chymosin-induced milk gel did not form. Adding heated (70°C for 5min) serum from any of the species to milk did not influence plasmin-induced hydrolysis of caseins or chymosin- or pepsin-induced coagulation of milk, suggesting that the inhibitor(s) is heat labile. Plasmin- or chymosin-induced hydrolysis of small synthetic substrates was not influenced by blood serum. It is suggested that -macroglobulin may be the inhibitory substance, although further study is required to verify this. [Copyright &y& Elsevier]

High-pressure (HP) treatment of food products is a novel processing technique during which the product is treated in a vessel of suitable strength at a high pressure, generally in the range 100–1000 MPa. As a result, several constituents and properties of the treated product are altered. HP-induced changes in the constituents and properties of milk are arguably among the most extensive of the range of food products studied to date. HP treatment of milk induces solubilization of minerals associated with the casein micelles, denatures whey proteins and, depending on pressure, can either induce aggregation or disruption of the casein micelles. These HP-induced changes in milk constituents affect the properties of the milk; cheesemaking properties of milk can be enhanced considerably, indicating potential application of HP treatment in this area; furthermore, encouraging results have also been reported for HP treatment of milk prior to yogurt manufacture. HP treatment of milk also affects its microflora; however, considerable variation in baroresistance between bacterial species and strains exists. Further applied research appears warranted to establish the full commercial potential of HP treatment of milk. [ABSTRACT FROM AUTHOR]

Abstract: High pressure (HP)-induced changes in the proteins of bovine milk have become an area of considerable research interest in recent years; as a result, there is now a detailed understanding of the effects of HP on casein micelles and whey proteins. HP treatment at pressures >400 or >100 MPa denatures the two most abundant whey proteins, α-lactalbumin (α-la) and β-lactoglobulin (β-lg), respectively. The majority of denatured β-lg in HP-treated milk associates with the casein micelles, although some denatured β-lg remains in the serum phase or is attached to the milk fat globule membrane; HP-denatured α-la is also associated with the milk fat globules. Casein micelles are disrupted on treatment at pressures >200 MPa; the rate and extent of micellar disruption increases with pressure and is probably due to the increased solubility of calcium phosphate with increasing pressure. On prolonged treatment at 250–300 MPa, reassociation of micellar fragments occurs through hydrophobic bonding; this process does not occur at a pressure >300 MPa, leading to considerably smaller micelles in such milk. As a result of HP-induced changes, the size, number, hydration, composition and light-scattering properties of casein micelles in HP-treated milk differ considerably from those in untreated milk. [Copyright &y& Elsevier]

The influence of added lyophilized butter serum on the heat stability of milk was investigated. The addition of lyophilized serum from salted butter to unconcentrated skimmed milk (SM) reduced the heat coagulation time (HCT) at, and increased the pH of, the maximum in the pH–HCT profile and caused disappearance of the minimum. NaCl had similar effects on the heat stability of SM as lyophilized salted butter serum, whereas lyophilized serum from unsalted butter had little effect. The addition of lyophilized salted butter serum to concentrated skimmed milk (CSM) also shifted the pH of maximum heat stability to a higher value and, at certain concentrations, increased the maximum HCT; similar effects were obtained on addition of NaCl, but lyophilized serum from unsalted butter had little effect. These results suggest that the effects of lyophilized serum from salted butter on the heat stability of SM or CSM are due primarily to the presence of a high level of NaCl in this serum. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the effect of high pressure (HP) treatment (0–30 min at 100–600 MPa at 20 °C, where treatment for 0 min implies the immediate release of pressure after reaching the desired level) on the rennet coagulation and cheese-making properties of milk heated at 90 °C for 10 min was investigated. Unpressurised heated milk or heated milk treated for 0 min at 100 MPa was not coagulable by rennet; however, heated milk treated at 250–600 MPa for 0–30 min had a rennet coagulation time (RCT) equal to, or lower than, that of unheated unpressurised milk; RCT decreased with increasing pressure and treatment time. The strength of the rennet-induced coagulum from heated milk treated at 250–600 MPa for 30 min or 400 or 600 MPa for 0 min was considerably higher than that of unheated unpressurised milk. Furthermore, the yield of cheese curd from HP-treated heated milk was ∼15% higher than that from unheated unpressurised milk and the protein content of the whey was ∼30% lower, regardless of pressure or treatment time, whereas the moisture content of the curd was not significantly influenced. These results indicate that by the application of a heat treatment, followed by a HP treatment, milk with superior rennet coagulation and cheese-making properties can be obtained. Industrial relevance: Heat treatment and high pressure (HP) treatment have received considerable research attention as a means for increasing the yield of cheese curd. However, neither is attractive on its own; in the case of heating because it impairs other cheese-making properties of milk, whereas increases in curd yield by HP treatment of milk can be achieved only at economically unattractive long treatment times. However, when milk is heat-treated (10 min at 90 °C) and subsequently HP-treated at a pressure ≥250 MPa, an increase in the yield of cheese curd by ∼15% can be obtained, while the strength of the renneted milk gel is increased and the rennet coagulation time is reduced. These effects can even be obtained when the pressure is released immediately after the desired level is reached. [Copyright &y& Elsevier]

High pressure (HP) treatment of milk alters many of its constituents and properties; in this study, HP-induced changes in casein micelles were examined. HP treatment of milk at 250 MPa increased casein micelle size by ∼30%, whereas treatment at 400 or 600 MPa reduced it by ∼50%. Pre-denaturing whey proteins in milk by heat treatment or preventing interactions between β-lactoglobulin and κ-casein, by addition of sulphydryl-blocking or reducing agents to milk prior to HP treatment, had little influence on HP-induced changes in casein micelle size. Addition of ethanol to milk, prior to HP treatment, resulted in the formation of large casein aggregates. On treatment at 250 MPa, larger increases in casein micelle size were observed in milk reconstituted from larger micelles, suggesting that increases in micelle size at this pressure are probably due to the formation of casein aggregates. HP treatment reduced the L*-value of milk; these changes were rapidly reversed on storage of milk at 37 °C, but maintained on storage at 5 °C. Similar to untreated milk, micelles in HP-treated milk were susceptible to dissociation by urea and tri-sodium citrate. Altered properties of casein micelles in HP-treated milk may influence the properties of products made from such milk. [Copyright &y& Elsevier]

In this study, reversibility of high pressure (HP)-induced solubilisation of αs1- and β-casein and HP-induced changes in micellar hydration and levels of ultracentrifugally-sedimentable solids in raw skim milk were examined. HP treatment of milk at 100–600 MPa resulted in considerable solubilisation of αs1- and β-caseins, with the extent of solubilisation reaching a maximum around 250 MPa. HP-induced solubilisation of caseins was probably a result of solubilisation of colloidal calcium phosphate and disruption of hydrophobic interactions. On storage of HP-treated milk at 5°C, dissociation of caseins was largely irreversible but at 20°C, considerable reassociation of caseins was observed. Hydration of the casein micelles was increased by HP treatment at 100–600 MPa, possibly due to HP-induced interactions between caseins and whey proteins; these changes were more extensive at higher pressures. The level of ultracentrifugally sedimentable solids was reduced by HP treatment, with a minimum occurring at 250 MPa; Changes in micellar hydration and the level of ultracentrifugally sedimentable solids were largely irreversible at 5°C, but partially reversible at 20°C. These results indicate that HP treatment increases levels of αs1- and β-caseins in the soluble phase of milk and produces casein micelles with different properties compared to those in untreated milk; therefore, HP treatment may have a considerable influence on the processing characteristics of milk. [Copyright &y& Elsevier]

Cheesemaking properties of milk are affected by high pressure (HP) treatment; this study focussed on HP-induced changes in curd yield. Yield was not influenced by treatment at pressures ≤250 MPa, but at higher pressures, curd yield was increased, by up to 25% after treatment at 600–800 MPa. In parallel with increased curd yield, increased curd moisture content and reduced protein content in the whey were observed after treatment at such pressures. Denaturation of α-lactalbumin or β-lactoglobulin occurred at >400 or >100 MPa, respectively. Curd yield and curd moisture content increased and protein content in the whey decreased with increasing treatment time (0–30 min of treatment at 400 or 600 MPa). Increased curd yield is probably a result of both the incorporation of denatured whey proteins and enhanced moisture retention in the curd. HP-induced increases in curd yield may indicate possible applications of HP treatment of milk for cheese manufacture. [Copyright &y& Elsevier]

Despite having well-documented effects on several constituents of milk, high pressure (HP) had little overall effect on the heat stability of raw, pre-heated or serum protein-free skim milk at pH values in the range 6.1–7.0. HP treatment at 600 MPa considerably increased the heat stability of concentrated skim milk at pH values >6.7. The ethanol stability of raw skim milk was reduced by HP treatment, shifting the somewhat sigmoidal ethanol stability versus pH profile to more alkaline values; however, these changes were partially reversible during subsequent storage at 5°C for 24 h. Ethanol-mediated temperature-induced dissociation of casein micelles occurred in both untreated and HP-treated milk and was not dependent on storage of milk subsequent to HP treatment. These findings provide further insight into how the HP-induced changes in the constituents of milk influence milk properties. [Copyright &y& Elsevier]

Creaming of raw whole bovine milk at refrigeration temperatures is generally regarded as an undesirable phenomenon; traditionally, creaming is prevented by homogenising the milk. The effects of high pressure (HP) processing on the creaming of raw whole bovine milk were examined in this study. HP treatment at pressures ≤250 MPa increased the rate and level of creaming, whereas treatment at ≥400 MPa reduced both of these parameters. On treatment at 200 or 600 MPa, creaming increased or decreased, respectively, with increasing treatment time. At 400 MPa, HP-induced changes in the rate and level of creaming were strongly treatment time-dependent. Treatment at 100–600 MPa for 0–60 min had little effect on milk fat globule size, whereas the viscosity of skimmed milk increased with increasing pressure and treatment time. The amount of milk protein associated with the milk fat globules was increased by HP treatment, the extent of the increase being maximal at 200 MPa. Although increased viscosity and the level of protein associated with the fat globules may partially explain the reduced rate and level of creaming, HP-induced aggregation and denaturation of agglutinins and lipoproteins are likely to have significant effects on HP-induced changes in the creaming characteristics of milk. [Copyright &y& Elsevier]

High pressure (HP) treatment has significant and, in many cases, unique effects on many constituents of milk. The structure of casein micelles is disrupted and the whey proteins, α-lactalbumin and β-lactoglobulin, are denatured, with the former being more resistant to pressure than the latter. Pressure-induced shifts in the mineral balance in milk also occur and moderately high pressures (100–400 MPa) induce the crystallisation of milk fat. However, milk enzymes seem to be quite resistant to pressure. As a result of pressure-induced effects on individual milk constituents, many properties of milk are affected. HP treatment increases the pH of milk, reduces its turbidity, changes its appearance, and can reduce the rennet coagulation time of milk and increase cheese yield, thereby indicating potential applications in cheese technology. However, to fully understand the effects of HP treatment on milk and to evaluate the full potential of this process in dairy technology, further research is required in several areas, including the reversibility of pressure-induced changes in milk and the physical stability of HP-treated milk. [Copyright &y& Elsevier]

In this study, protein and salt distributions in the milk of 48 Holstein-Friesian cows were studied. Gross composition of milk samples and variation between individual cows was in line with expectation. However, the mineralisation of the casein fraction, expressed in mmol protein-associated calcium per 10 g casein, differed >2-fold between the milk samples. Reasons for this variation are unknown and could not be correlated to casein composition and/or genetic variants of caseins. Furthermore, notable differences (>5-fold) in non-sedimentable (100,000× g for 60 min) casein were observed. Percentages of non-sedimentable caseins differed for κ-casein genetic variants (BB > AB > AA) and increased with increasing degree of glycosylation. Higher levels of non-sedimentable caseins with increasing degree of glycosylated κ-casein could be attributable to increased repulsion between the micelles, leading to the formation of a less cohesive sediment on centrifugation. [ABSTRACT FROM AUTHOR]

Acidification is an important process in the production of several dairy products and has an impact in taste, viscosity, and shelf life of the products. This paper deals with the development of an empirical mathematical model to describe milk acidification in terms of pH dynamics. The model is built upon experiments of pasteurized skimmed milk acidification for acid-induced casein precipitation and extended to predict the partitioning of calcium and phosphates in the whey and the dynamics of pH during fermentation of yoghurt manufacture. Furthermore, the model can be used directly or in optimization problems to provide recommendations about product design. [ABSTRACT FROM AUTHOR]