The objective of the studies reported in this research communication was to investigate differences in composition and enzymatic activities in bulk milk samples provided from Swedish dairy farms with different management systems, i.e. automated (AMS) and conventional milking systems (CMS). A bulk milk sample was collected from each of 104 dairy farms, 51 using AMS and 53 using CMS, located in the same geographical region. Sampling took place within two consecutive days during the indoor period (October). Milk samples were analysed for contents of total fat and protein, free fatty acids (FFA), caseins and whey proteins, somatic cell count (SCC), pH, plasmin and plasminogen derived activities, and total proteolysis. Our results showed a lower protein content and higher SCC in bulk milk from AMS herds compared with milk from CMS herds. Plasmin, plasminogen and total plasmin/ plasminogen derived activities were lower in milk from AMS herds but despite this, total casein and the ß-casein fraction as % of total protein were lower in milk from AMS herds than in milk from herds using CMS. Total proteolysis was higher in milk from AMS herds, suggesting that other proteases than plasmin, e.g. cellular and bacterial proteases, contributed to the degradation of casein. This was supported by a positive correlation between SCC and total proteolysis (P < 0·01), as well as a negative correlation between total proteolysis and ß-casein fraction (P < 0·05). In conclusion, comparing the quality of bulk milk from commercial dairy herds using AMS and CMS, respectively, several differences were observed, suggesting a significant effect from management system.

The prevalence of type 2 diabetes mellitus (T2DM) is increasing and it is estimated that by 2030 approximately 366 million people will be diagnosed with this condition. The use of dipeptidyl peptidase IV (DPP-IV) inhibitors is an emerging strategy for the treatment of T2DM. DPP-IV is a ubiquitous aminodipeptidase that cleaves incretins such as glucagon like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), resulting in a loss in their insulinotropic activity. Synthetic DPP-IV drug inhibitors are being used to increase the half-life of the active GLP-1 and GIP. Dietary intervention is accepted as a key component in the prevention and management of T2DM. Therefore, identification of natural food protein-derived DPP-IV inhibitors is desirable. Peptides with DPP-IV inhibitory activity have been identified in a variety of food proteins. This review aims to provide an overview of food protein hydrolysates as a source of the DPP-IV inhibitory peptides with particular focus on milk proteins. In addition, the proposed modes of inhibition and structure–activity relationship of peptide inhibitors are discussed. Milk proteins and associated peptides also display insulinotropic activity and help regulate blood glucose in healthy and diabetic subjects. Therefore, milk protein derived peptide inhibitors may be a unique multifunctional peptide approach for the management of T2DM.

Bulk tank ewe's milks with low (<500,000 ml−1), medium (1,000,000–1,500,000 ml−1) and high (>2,500,000 ml−1) somatic cell counts (SCC) from three breeds were used to manufacture hard ewes’-milk cheese. Physico-chemical analysis and capillary electrophoresis of fresh cheeses and cheeses that had been ripened for 1, 2, 3 and 6 months were carried out. The results showed that high SCC levels in milk affected the moisture content of only freshly made cheeses and the pH, fat content and fat acidity of ripened cheeses. Regarding proteolysis, the levels of all β-CNs in freshly made cheeses were significantly lower as the SCC values increased and the Castellana breed was the most affected by SCC levels because a significant decrease in all α-CNs was also observed as SCC levels rose. Analysis of the casein profile by principal component analysis (PCA) revealed that there were no clear differences according the SCC up to the third month. However in the third and sixth months cheeses with low levels of SC were closely grouped and characterised by the highest levels of intact caseins. Regarding the effect of breed, the results point to a more intense proteolytic activity in the Assaf breed, whose more matured cheeses showed the highest content of casein proteolytic fragments.

The changes in milk fat globules and fat globule surface proteins of both low-preheated and high-preheated concentrated milks, which were homogenized at low or high pressure, were examined. The average fat globule size decreased with increasing homogenization pressure. The total surface protein (mg m−2) of concentrated milk increased after homogenization, the extent of the increase being dependent on the temperature and the pressure of homogenization, as well as on the preheat treatment. The concentrates obtained from high-preheated milks had higher surface protein concentration than the concentrates obtained from low-preheated milks after homogenization. Concentrated milks heat treated at 79°C either before or after homogenization had greater amounts of fat globule surface protein than concentrated milks heat treated at 50 or 65°C. This was attributed to the association of whey protein with the native MFGM (milk fat globule membrane) proteins and the adsorbed skim milk proteins. Also, at the same homogenization temperature and pressure, the amount of whey protein on the fat globule surface of the concentrated milk that was heated after homogenization was greater than that of the concentrated milk that was heated before homogenization. The amounts of the major native MFGM proteins did not change during homogenization, indicating that the skim milk proteins did not displace the native MFGM proteins but adsorbed on to the newly formed surface.

The incorporation of caseins and whey proteins into acid gels produced from unheated and heat treated skimmed milk was studied by confocal scanning laser microscopy (CSLM) using fluorescent labelled proteins. Bovine casein micelles were labelled using Alexa Fluor 594, while whey proteins were labelled using Alexa Fluor 488. Samples of the labelled protein solutions were introduced into aliquots of pasteurised skim milk, and skim milk heated to 90 °C for 2 min and 95 °C for 8 min. The milk was acidified at 40 °C to a final pH of 4·4 using 20 g glucono-delta-lactone/l (GDL). The formation of gels was observed with CSLM at two wavelengths (488 nm and 594 nm), and also by visual and rheological methods. In the control milk, as pH decreased distinct casein aggregates appeared, and as further pH reduction occurred, the whey proteins could be seen to coat the casein aggregates. With the heated milks, the gel structure was formed of continuous strands consisting of both casein and whey protein. The formation of the gel network was correlated with an increase in the elastic modulus for all three treatments, in relation to the severity of heat treatment. This model system allows the separate observation of the caseins and whey proteins, and the study of the interactions between the two protein fractions during the formation of the acid gel structure, on a real-time basis. The system could therefore be a valuable tool in the study of structure formation in yoghurt and other dairy protein systems.

The effects of high pressure treatments (100–300 MPa; 15 min; 9 °C or 20 °C) on the distribution of minerals and proteins of raw skim milk (RSM) and of a dispersion of industrial phosphocaseinate (PC) were studied after separation of the micellar and soluble phases by ultracentrifugation (UCF). Whatever the temperature of high pressure treatments, the pressure-induced dissociation of the casein micelles was accompanied by calcium (Ca), phosphorus (P) and casein release from the micelles. The released Ca and P were or became bound to soluble proteins since progressive increases in Ca and P concentrations were observed in the UCF supernatants of RSM and of the PC dispersion but not in the ultrafiltrates from these UCF supernatants (free of soluble proteins). Simultaneously, αS1-, αS2-, β- and κ-caseins were progressively released from the micelles, as seen by electrophoretic analysis. The pressure-induced solubilisation of αS1- and αS2-caseins, essentially located in the core of the micelles, suggests that high pressure destabilised micelles including their internal structure.

Changes in nitrogen compounds during ripening of 40 batches of Manchego cheese made from raw milk (24 batches) or pasteurized milk (16 batches) at five different dairies throughout the year were investigated. After ripening for six months, degradation of p-κ- and β-caseins was more intense in raw milk cheese and degradation of αs2-casein in pasteurized milk cheese. Milk pasteurization had no significant effect on breakdown of αs1-casein. Hydrophobic peptide content did not differ between raw and pasteurized milk cheese, whereas hydrophilic peptide content was higher in raw milk cheese. There were no significant differences between seasons for residual caseins, but hydrophobic peptides were at a higher level in cheese made in autumn and winter and hydrophilic peptides in cheese made in winter and spring. Raw milk cheese had a higher content of total free amino acids and of most individual free amino acids than pasteurized milk cheese. The relative percentages of the individual free amino acids were significantly different for raw milk and pasteurized milk cheeses. The relative percentages of Lys and Ile increased, while those of Val, Leu and Phe decreased during ripening. There were also seasonal variations within the relative percentages of free amino acids. In raw milk cheeses, Asp and Cys were relatively more abundant in those made in autumn, Glu and Arg in cheeses made in winter, and Lys and Ile in cheeses made in spring and summer. Biogenic amines were detected only in raw milk cheese, with the highest levels of histamine, tryptamine and tyramine in cheeses made in spring, winter and spring, respectively.

The changes in milk fat globules and fat globule surface proteins during concentration of whole milk using a pilot-scale multiple-effect evaporator were examined. The effects of heat treatment of milk at 95 °C for 20 s, prior to evaporation, on fat globule size and the milk fat globule membrane (MFGM) proteins were also determined. In both non-preheated and preheated whole milk, the size of milk fat globules decreased while the amount of total surface proteins at the fat globules increased as the milk passed through each effect of the evaporator. In non-preheated samples, the amount of caseins at the surface of fat globules increased markedly during evaporation with a relatively small increase in whey proteins. In preheated samples, both caseins and whey proteins were observed at the surface of fat globules and the amounts of these proteins increased during subsequent steps of evaporation. The major original MFGM proteins, xanthine oxidase, butyrophilin, PAS 6 and PAS 7, did not change during evaporation, however, PAS 6 and PAS 7 decreased during preheating. These results indicate that the proteins from the skim milk were adsorbed onto the fat globule surface when the milk fat globules were disrupted during evaporation.

Effects of atropine on blood plasma amino acid profile and on the yields and concentration of milk components were investigated in 12 Friesian cows in early lactation. Cows were housed indoors and fed with cut pasture ad libitum. Each cow received four treatments over 12 d during a replicated 4×4 Latin square experiment. Treatments were: control (saline); low dose (L; 30 μg atropine/kg body weight (BW)); medium dose (M; 40 μg atropine/kg BW); and 2×L dose, 2 h apart (2×L). On each of four treatment days, cows were milked at about 7.00, after which treatments were administered by subcutaneous injection. Cows were milked again at 2 h, 6 h and 10 h after injection. Milk samples were collected at each milking. Immediately after the 2 h milking, blood samples were drawn from each cow and the second injection was given for the 2×L treatment. Atropine reduced hourly milk yield, and concentrations and hourly yields of total protein, casein, whey protein, α-casein, β-casein, κ-casein, β-lactoglobulin and α-lactalbumin, but by differing amounts. Milk concentrations of bovine serum albumin and immunoglobulin G were increased by atropine, and overall yields of these proteins were mostly unchanged. Atropine lowered concentrations of most, but not all, amino acids in blood plasma, with essential amino acids reduced more than non-essential amino acids. Concentrations of α-amino N in whole blood, and glucose and insulin in blood plasma, fell after atropine injection. There was no difference between the L and M doses of atropine, but the 2×L dose had greater effects on milk composition than the single doses. For yields of milk and milk components, the effect of the 2×L dose was also more persistent. The results highlight the differential synthesis of individual milk proteins, and suggest that atropine might be useful for evaluating the mechanisms regulating milk protein composition.

Here we report the entire cDNA sequences for equine αS1-, β- and κ-casein. Based on interspecies comparison, nine exons were found in equine β-casein and five in κ-casein. In equine αS1-casein cDNA the exon 5 was missing, which resulted in the total of 18 exons instead of 19 theoretically possible exons in αS1-casein cDNA. Comparison of DNA sequences representing exon 5 in other species with corresponding equine genomic region confirmed the presence of cryptic exon in horse genomic DNA. Equine αS1-casein mRNA was present in three forms in the lactating mammary gland and we showed that the two shorter forms were produced by skipping either the exon 8 or exon 15. In horse, as in some other mammals, β- and κ-casein are considerably more conserved (sequence identity 53% to 59% and 57% to 67%, respectively) than αS1-casein which appears as the most variable casein among species (sequence identity 40% to 54%). Interestingly, horse caseins resemble human much more than bovine caseins which may also explain the high dietetic value of mares' milk.