The effects of varying salt contents and cream-cooling treatments on thermograms of the resultant butters were determined by differential scanning calorimetry (DSC). A procedure is described for loading the calorimeter without erasing the thermal history of the sample. Unsalted butter had only one melting transition associated with the aqueous phase, at −0·5 °C. Salted butters had two such transitions. One occurred at a constant −22 °C and corresponded to melting of a NaCl–water eutectic mixture. The other varied with the salt content and probably corresponds to melting of the ice in a NaCl solution. Slow-cooling treatment of cream resulted in butter thermograms similar at 10 and 25 °C to those from the Alnarp treatment, but differed between 22 and 25 °C. Shock-cooling resulted in higher amounts of crystallization than the other 2 treatments. The DSC was shown to be useful in following the effects of cream treatment upon the melting characteristics of the resulting butter.

Deposit formation from the milk of 2 individual cows was measured throughout lactation, using the hot-wire laboratory apparatus previously described. The amount of deposit fell slightly to a minimum at about the tenth week of lactation, and then rose to a maximum towards the end of lactation. The ratio of the maximum to the minimum was about 2:1. No correlation was found between amount of deposit and the fat, solids-not-fat, ash and calcium contents of the milks. The presence of mastitis in 1 cow and the administration to it of antibiotics did not affect the amount of deposit formed from its milk.

Milk protease, the naturally occurring proteolytic enzyme from fresh raw bovine milk, was purified 629-fold. Purification methods are described which included acid precipitation, ion-exchange and gel chromatography and ammonium sulphate fractionation. It was necessary to use a large-scale purification as the amounts of enzyme in milk are very low.

The basic properties of the enzyme were elucidated from experiments on this partially purified fraction. Under the conditions of assay these showed a wide pH optimum from 6·5 to 9·0 and a temperature optimum of 37°C. The protease was fairly heat stable, the stability being pH dependent.

The source of the enzyme appeared to be the mammary gland, where the enzyme was also detected.

The dephosphorylation of β-casein, type A1, by dilute aqueous solutions of sodium hydroxide has been studied. It has been found that the mechanism whereby inorganic phosphate is liberated by the action of alkali is one of β-elimination from O-phosphoserine residues which are themselves converted initially to dehydroalanyl residues.

Ceramide, an N-acyl derivative of sphingosine bases, has been isolated for the first time from bovine milk in the free form and its constitution studied. Sixteen component fatty acids were found, among which C23:0 (38·1%), C24:0 (29·5%), C22:0 (17·9%) and C16:0 (7·2%) were predominant. Seven component long-chain bases were detected. The principal bases were C18-sphingosine (35·0%) and C16-sphingosine (31·6%).

Solid fractions obtained by a commercial process from anhydrous milk fat were refractionated and the softening point (SP), iodine value (IV), and melting thermograms determined. The content of high melting fats and liquid fat content at the SP were calculated for each fraction from its thermogram. Refractionation at 28 °C did not alter the properties of the resultant solid fat. The small amount of liquid fat obtained by refractionation resembled intact milk fat in the properties measured. Refractionation at 31–32 °C yielded a solid fat having a higher SP, lower IV, and increased high melting fat content. Triple refractionation resulted in a solid fraction having a restricted melting range and capable of crystallizing in an unstable polymorphic form upon quick cooling. Tempering the refractionated solid fats at the melting gap temperature of 20–22 °C resulted in elimination of phases melting below −10 °C and enhancement of the melting gap. The content of high melting fat was correlated with the SP. The SP occurred when 95 % of the fat (S.D.±2·7 %) had melted.

An investigation was made into the effect of subclinical mastitis on the accuracy of the Amido Black method for measuring the crude-protein percentage of the milk of individual cows. Values obtained by the dye-binding and Kjeldahl methods on a sample of milk from each quarter of 46 cows, 11 of which were sampled at regular intervals during lactation, were compared. It was concluded that, even in cases of severe subclinical mastitis, the effect is so small as to constitute no objection to the use of the dye-binding method. The accuracy of the Amido Black method, irrespective of disease, was less in milk produced in the first and last months of lactation.

The kinetics of the release of glycopeptides by the action of rennin on bovine whole milk have been studied. The initial rate of release of glycopeptides was proportional to the concentration of rennin. Using the integrated form of the Michaelis–Menten equation, values have been obtained for Km and V. These values varied between milk samples from individual cows, and for a single milk sample the value for Km increased with increasing rennin concentration. It is suggested that the Km value is partly dependent on the carbohydrate composition of individual κ-casein molecules.

The milk-clotting enzyme found in the flowers of Cardo (Cynara cardunculus) was investigated as to its suitability as a substitute for traditional animal rennet used in cheese-making. The influence of milk pH, temperature and quantity on the clotting activity of this enzyme was studied. Rheological behaviour of cow's-milk and sheep-milk curds, from renneting to cutting, was determined with the Plint cheese curd torsiometer for various Ca contents and pH values. Edam, Serra and Roquefort cheeses were made and the protein breakdown which occurred in the cheese during the ripening period was determined. Animal rennet was used as a control in all the experiments. The enzyme from Cardo was a satisfactory substitute for animal rennet with cow's milk and was even more suitable for sheep's milk. It was found to be a very good clotting enzyme for soft-bodied cheese like Serra, but because of its high proteolytic activity it presented some problems in Edam cheese-making. In Roquefort cheese it gave satisfactory results, but with some loss in yield.

The effects of feeding lactating cows a daily supplement of 1 kg formaldehyde-treated casein–safflower oil (1:1, w/w) on the milk composition are reported. Three breeds, Jersey, Sahiwal and Sahiwal × Jersey crossbred were used.

The formaldehyde treatment not only eliminated the suppressing effect on the milk, fat and protein yields and on the fat and protein contents usually encountered when such a level of unsaturated oil is fed to lactating cows, but also resulted, on the average, in 15 and 6% increases in the fat and protein contents respectively.

The formaldehyde-treated dietary supplement also caused a decline of 5% in the solids-not-fat content, presumably due to a decrease in the lactose content.

It is suggested that the formaldehyde treatment protects the casein from the ruminal proteolysis and this in turn prevents the encapsulated unsaturated oil from biohydrogenation and eliminates the diverse effects on rumen microflora and environment.

The rennin coagulation time of cow's milk was inversely proportional to the amount of glycopeptides released by rennin action on the milk and to the initial velocity of the release of the glycopeptides. It was shown that the rennin coagulation of milk is largely determined by the primary phase of rennin action and, therefore, by the amount of κ-casein that is susceptible to attack by rennin.

When milk was chilled for 12 and 24 h at 0 °C, a decrease in the calcium and phosphorus contents of the casein micelle of both buffalo and cow's milk was observed. This decrease was directly proportional to the cooling period. A proportionate increase with cooling in the sialic-acid content of the casein micelle of chilled milk was noticed. Casein micelle isolated from chilled milk exhibited low opacity compared with the normal counterpart.

A decrease in micellar casein and an increase in soluble casein were observed in both buffalo and cow's milk, in proportion to the cooling period. Similar results were obtained when casein micelles were resuspended in milk dialysate and centrifuged.

Casein micelles from chilled milk showed different patterns on starch-gel electrophoresis compared with normal micelles. The intensity of the κ-casein band was relatively higher in the chilled samples. Gel-filtration studies suggest that some molecular rearrangement occurs in the casein micelle when milk is chilled.

The release of sialopeptide from micellar casein by rennet was not influenced by chilling. However, a decrease in the rate of turbidity development in renneted suspensions of casein micelles was noted in chilled milk, which suggests a change in the structure of the casein micelle.

No difference was noticed between buffalo and cow's milk in these respects.

The plasma levels of individual amino acids were studied in 6 dairy cows from 4 days before to 3 days after calving. During this sampling period, the concentrations of 13 amino acids showed significant changes. The levels of several amino acids were depressed markedly in the sample collected immediately before calving. Following parturition, the concentration of most amino acids gradually returned to values obtained 3 days before calving. The glutamine and alanine contents of the plasma rose to a peak value 1 day after calving and subsequently decreased. The mean concentrations of glycine and α-aminobutyric acid did not change before parturition but rose significantly thereafter. These observations are discussed in terms of amino-acid utilization for milk protein synthesis and gluconeogenesis at the onset of lactation. The changes in plasma amino acid levels appear to be synchronized with those reported for prolactin and progesterone in the 24 h before parturition. This may indicate an important influence of both hormones on the lactogenic process in the cow. The highly significant correlations obtained between the concentrations of 14 individual amino acids are discussed.

This study reports the effect of feeding formaldehyde-treated or untreated spray-dried casein–safflower oil (1:1, w/w) particles on the fatty-acid composition of milk and plasma lipids of cows.

When the formaldehyde-treated particles were given to Jersey, Sahiwal and Jersey × Sahiwal crossbred cows (1 kg per cow per day) the linoleic acid (18:2) present in the safflower oil was not hydrogenated by the rumen micro-organisms and was incorporated into milk fat.

When the untreated supplement was fed, however, the 18:2 fatty acid was hydrogenated in the rumen and there was an increased proportion of octadecenoic acid (18:1) in the milk fat.

The increased proportions of 18:2 (treated supplement) and 18:1 (untreated supplement) were associated with decreased proportions of palmitic (16:0) and myristic (14:0) acids in the milk fat. All 3 breeds showed similar responses.

The fatty-acid composition of plasma triglycerides, which are an important source of long-chain fatty acids for mammary-gland lipogenesis, was similarly affected. Furthermore, there were significant changes in the fatty-acid composition of other plasma lipids (e.g. phospholipids and cholesteryl esters). The interrelationships between dietary, plasma and milk fatty-acid compositions are discussed.

A large number of samples (433) from the milk of Friesian herds was taken during the period November 1968 – September 1969, and a smaller number (159) from Jersey herds during the dairy ‘season’ September 1969 – April 1970, and analysed for total nitrogen (TN) and for non-protein nitrogen (NPN). The Friesian milk sample varied in TN from 0·456 to 0·624% (average 0·531 ± 0·021%) and in NPN from 0·024 to 0·054% (average 0·035 ± 0·004%). The Jersey samples varied in TN from 0·467 to 0·718% (average 0·584 ± 0·036%) and in NPN from 0·022 to 0·051% (average 0·033 ± 0·006%).The average NPN value for all the milks was 0·034 ± 0·005%.

There was a seasonal trend in NPN and TN for the Jersey and in TN but not in NPN for the Friesian milks. The proportion of NPN as a percentage of TN varied widely – for the Friesian samples from 4·9 to 10·2% (average 6·46%) and for the Jersey samples from 3·7 to 8·7% (average 5·74%).

Urea N also was estimated in 125 of the Friesian and in all the Jersey milk samples. It varied from 0·012 to 0·029% (average 0·020 ± 0·004%) in the Friesian and from 0·009 to 0·031% (average 0·020 ± 0·004%) in the Jersey samples. For all the milks the urea N as a percentage of NPN varied from 33 to 79 (average 56·5%).

It is suggested that values for ‘protein content’ of milk should refer only to ‘true’ protein ((TN – NPN) × 6·38) and that in the absence of an analytical result for NPN the use of an average value such as that above would be justified.

Domiati cheese from homogenized and unhomogenized pasteurized milk was pickled for 4 months at room temperature. During pickling, the soluble tyrosine and tryptophan contents of the cheese gradually increased, indicating progressive proteolysis.

Gel filtration of cheese extract on Sephadex G-25 revealed the presence of nitrogenous substances of various molecular weights. The maximum formation of amino acids and related substances was observed after 15 days storage.

The changes in the electrophoretic patterns of proteins in the cheese during pickling indicated that both αs - and β-caseins were attacked. β-Casein, however, was much less affected.

Homogenization was found to affect the formation of soluble nitrogenous substances, but was without effect on the electrophoretic pattern of the protein in the cheese.

The flavours of the following compounds were determined in synthetic butter prepared from 84% steam-deodorized butter oil and 16% water: C6, 8, 10, 12, 14 δ-lactones, C12 γ-lactone, C2, 4, 6, 8, 10, 12, 14n-alkanoic acids, phenol, m- and p-cresols, o-methoxyphenol, indole and skatole. C6, 8, 10 δ-lactones, C2, 4, 6, 8, 10, 12, 14n-alkanoic acids, phenol, m- and p-cresols, o-methoxyphenol and volatile fractions from butter oil were also evaluated in bland butter. None of the compounds listed constitute basic butter flavour on their own, but C8, 10 δ-lactones, C10 acid, phenol, p-cresol, indole and skatole contribute to butter flavour.

The adsorption of whole casein and some of its constituent caseins by halloysite and kaolinite in the presence and absence of urea and 2-mercaptoethanol has been studied. The order of adsorption generally observed for both clays in the absence of urea and 2-mercaptoethanol was temperature sensitive casein component (TS) > αs1-casein B > αs1-casein A > β-casein in the pH range 7·5–9·5, confirming that these two clays have structurally similar surfaces. In the presence of urea and 2-mercaptoethanol the rate of adsorption on to halloysite increased, although the quantity adsorbed decreased and the relative affinities of the major casein components at pH 8 were altered. However, urea and 2-mercaptoethanol did not alter the relative affinities of the caseins to kaolinite, although the quantity adsorbed did decrease. The casein components are probably adsorbed as monomers, and it may be the superior dispersing properties of the urea solution that decrease the amount adsorbed. The halloysite structure was altered by absorption of urea and the altered relative affinities of the various casein components in the presence of urea can be ascribed to that effect.

The results support the hypothesis that adsorption occurs because the energy of the system is lowered due to changes in protein-solvent, clay-solvent and solvent-solvent (solvent structuring), as well as to electrostatic interactions.

Changes in the microflora and titratable acidity of bovine colostrum stored at 4 and 30 °C were monitored for 21 days. Colostrum did not inhibit the indigenous microflora, and increased titratable acidity may have accounted for the observed decrease in the numbers of Enterobacteriaceae after an initial rapid growth period.

A method for the partial fractionation of the αs-casein complex is described. It involves removal of κ-casein from iso-electric casein by the method of Zittle & Custer (1963) followed by fractionating the residue (αs- and β-casein) by the urea procedure of Hipp et al. (1952). αs0- and αs1-caseins precipitate from 3·3 M urea at pH 4·6, but much of the αs2-, αs3- and αs4-casein remains in solution and co-precipitates with β-casein from 1·7 M urea at pH 4·9. Chromatography on DEAE cellulose clearly separates β-casein from the αs2-, αs3- and αs4-caseins, which are not resolved by the conditions employed. The method is suitable for the fractionation of iso-electric casein into all its major components (i) κ-casein; (ii) αs0- and αs1-caseins; (iii) αs2-, αs3- and αs4-caseins; (iv) β-casein; (v) γ-casein.