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.

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.

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.

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.

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.

Five hundred and seven samples of iso-electric caseins were typed by starch-gel electrophoresis and their polymorphic compositions were determined in terms of αs1-, β- and κ-casein variants. Clotting times in minutes were determined on 50 ml of 3% casein solution in milk dialysate containing 0·02 M-Ca as CaCl2 and 2 mg commercial rennin powder at pH 6·60–6·80. The clotting times ranged from 4·06 to 7·41 min. The data indicated that the polymorphic composition of casein significantly influenced its stability to rennin. The polymorphic combinations αs1B+βA+κB and αs1B+βAC+κAB, were the most resistant to rennin action (clotting times of 7·41, 7·39 min respectively). The combinations αs1B+βB+κAB and αs1BC+βB+κB were the least resistant to rennin action (clotting times of 4·25 and 4·06 min respectively). In most cases, caseins with lower stability to rennin contained κB or βB or both in their composition.

The variations in the composition of milk over an 18-week period from lactating British Alpine and Anglo–Nubian goats imported into Trinidad are reported. The animals were fed Napier grass (Pennisetum purpureum) ad lib. and 2 lb of a proprietary concentrate mixture daily.

The mean percentage contents of the milks of British Alpine and Anglo–Nubian goats were: total solids 11·49±0·22, 12·17±0·28; butterfat 3·42±0·18, 4·06±0·22; total N 0·462±0·04, 0·530±0·07; ash 0·78±0·02, 0·79±0·03 and ‘lactose’ 4·38±0·28, 4·05±0·55. Anglo–Nubian goats had a higher content of percentage total solids, fat, total N and ash. For all constituents the coefficient of variation between weeks was higher for Anglo–Nubian goats. No significant trends were found between weeks for each of the components analysed for both breeds. Statistically significant correlations (P < 0·01) were found between percentage fat and percentage total N for both breeds.

The mean mineral contents (mg/100ml) for the milks of British Alpine and Anglo–Nubian goats were: Na 52·6±4·6, 55·5±1·9; K164·0±8·4, 133·4±11·4; Ca 85·5±11·6, 89·9±9·8; Mg 13·2±3·8, 10·2±1·6 and P 74·7±3·9, 82·1±3·9. British Alpine goat's milk had a higher content of K and that of Anglo–Nubian goats had a higher content of P; both differences were statistically significant (P < 0·01).

The milk composition figures in this study together with those from a similar study in Guadeloupe suggest that the values are low and considerably lower in comparison with the same breeds of goats in a temperate environment. This could be a feature of dairy goats imported into the tropics due perhaps to inadequate nutrition. Much more information is needed to verify this possibility.

The effect of heat treatment on the rennet coagulation times (RCTs) of various casein–whey protein systems, the effect of pre-renneting centrifugal serum on the RCT of casein subsequently mixed with such serum, the influence of repeated centrifugation and resuspension at constant protein level on the RCT of such suspensions, and the rate and completeness of the hydrolysis of sialic acid in micellar and non-micellar caseins, all lead to the conclusion that κ-casein does not occur in milk in 2 functionally different states, as proposed by Parry & Carroll (1969).

Storage of aseptically packed ultra-high-temperature (UHT) milk has been shown to be accompanied by pronounced changes in the molecular weight distribution of the pH 4·6 insoluble casein. These changes were both time-dependent and temperature-dependent, proceeding much more rapidly at 37 °C than at 30 °C, but even at 4 °C the changes were considerable. The proportions of high molecular weight material present before and after storage have been studied by gel filtration in dissociating solvents using Sephadex G-200. Measurements have also been made on casein material isolated from in-bottle sterilized milks and canned evaporated milk for comparison. The results of gel filtration have been compared with sedimentation coefficients recorded by ultracentrifugation and with changes in the content of amino groups titratable with trinitrobenzene-sulphonic acid. The results are compatible with the suggestion that the Maillard reaction occurred at ambient temperatures, and over a period of several months led to browning and sediment formation due to covalent cross-linking of polypeptide chains. The implications of this are discussed with reference to spoilage of UHT milk on storage and the phenomenon of gelation.

Radioactive labelling of intact fat globules with 125I gave at least one labelled protein in each of the 4 fractions of the fat globule membrane. Similar treatment of isolated membrane gave extensive labelling of all membrane proteins in each fraction.

It was concluded that all fractions are partially exposed at the membrane surface and the existence of well-defined layers is unlikely.

The effect of temperature and time of heating whole milk on the renninclotting time, the primary phase of rennin action and the protein (mainly β-lactoglobulin) soluble in 2% trichloroacetic acid (TCA), have been studied. Considerable changes in these parameters occurred above 60°C. The primary phase was inhibited (the degree of inhibition being both temperature and time-dependent), the clotting time was increased, and the protein soluble in 2% TCA decreased considerably.

It is suggested that the inhibition of the primary phase was due to complex formation between κ-casein and β-lactoglobulin, the increase in clotting time to a combination of complex formation and a change in the distribution of Ca, and the decrease in β-lactoglobulin to both its interaction with κ-casein and its heat denaturation. The relevance of such changes to the heat stability of milk is discussed.

Twenty-four Murrah buffalo cows were divided into 4 groups and were fed 0·3, 0·4, 0·5 or 0·6 kg of concentrate mixture per litre of milk produced. Energy and N balance studies were conducted on 2 animals from each group in the sixteenth and seventeenth weeks of the study. The efficiency of conversion of gross energy into milk energy ranged from 10·9 to 12·7%. The efficiency of conversion of metabolizable energy (ME) and ME above maintenance into milk energy ranged from 25·0 to 32·2% and from 51·7 to 78·6% respectively. Differences amongst groups were not significant for all the 3 parameters.

The conversion of digestible N into milk N varied between 23·6 and 27·3% in different groups. The efficiency of utilization of metabolizable N for milk production ranged between 47·6 and 56·4%. Various groups however did not differ significantly from each other in these respects.