In growing rats from 3 weeks to 3 months old, 0·1 % potassium thiocyanate (KSCN) decreased the plasma protein-bound iodine level by 47 % and the total DNA in the mammary gland by 11 %, but had no effect on the total KNA. Administration of thiocyanate in the form of 0·1, 0·3 and 0·5 % KSCN during pregnancy and 14 d of lactation lowered the protein-bound iodine level by 48–66 %, the total DNA by 11–47 % and the total RNA by 14–63 %, depending on the KSCN dosage. The 14-d-old litters of rats receiving thiocyanate weighed 4–41 % less than those in the control group.

The effect of intramammary infusion of Escherichia coli endotoxin upon mammary blood flow was studied in lactating goats and cows. Blood flow was recorded by means of an electromagnetic flow probe chronically implanted around one mammary artery.

Endotoxin mastitis was always accompanied by a significant increase in mammary blood flow, characterized by 2 conspicuous peaks. The flow returned to control values by the thirteenth hour after infusion. Other symptoms of acute mastitis were: fever, increased heart rate, swelling, heat and pain of the gland, increased chloride and total cell count in milk.

A new procedure is described for the preparation of cytoplasmic droplets from goat's milk and the metabolic potential of these droplets has been surveyed. Acetate was incorporated into fatty acids of varying chain lengths and acetate and glucose were oxidized to CO2 by these cytoplasmic droplets in vitro. There was a low rate of protein synthesis but no detectable DNA or lactose synthesis. It is concluded that the cytoplasmic droplets can provide an alternative to biopsy material for studying certain aspects of goat mammary lipid metabolism in vitro.

The composition of whole casein of 5 herd-bulk and 42 individual-cow milks from a single herd of Ayrshire cows has been determined. The percentage composition of the herd-bulk samples varied relatively little over a period of more than a year with the whole casein consisting on average of 38·4 % αs1,0-casein, 36·5 % β-casein, 12·5 % κ-casein, 10·5 % minor αs-caseins and 2·1 % γ-casein. For the individual-cow samples from mid-lactation, casein composition also was relatively constant, but in early and late lactation composition varied more with the relative amount of β-casein often being lower and those of κ- and γ-caseins often higher than in mid-lactation, these differences tending to be more marked in samples from older cows. Stage of lactation appeared to have little effect on the relative amounts of αs1,0-and minor αs-caseins.

The concentrations of all casein fractions were significantly positively correlated (P < 0·001) with the concentration of whole casein in the milk. Also, there were significant negative correlations (P < 0·001) between the percentages of whole casein present as β- and κ-caseins, β- and γ-caseins and minor αs- and γ-caseins, and a significant positive correlation (P < 0·001) between the relative amounts of κ- and γ-caseins. The relative amount of the major αs1,0-casein fraction, however, was not closely related to those of any of the other fractions.

Generally, milks with high lactose and low Na values yielded casein which was comparatively rich in β-casein and comparatively poor in κ- and γ-caseins.

The components of whole casein from water buffalo (Bubalis L.) have been re-investigated in the light of recent studies elucidating the primary structure of all the bovine caseins (αs1, αs2, β & κ). Whole casein samples obtained from individual Italian buffaloes all contained 2 αs1- and 2αs2-casein fractions. These 4 components were isolated and identified by their amino acid compositions and terminal amino acid sequences. The 2 αs1-casein fractions seem to have identical peptide chains as do the 2 αs2 fractions, with the individual fractions within each group differing only in their phosphate content. Buffalo β-casein was also isolated and characterized by its amino acid composition and terminal sequences. The isolation of different buffalo κ-casein fractions was reported earlier (Addeo, Chobert & Ribadeau-Dumas, 1977). These fractions were purified and analysed. They were found to have the same amino acid compositions and C-terminal sequences, but to differ in their carbohydrate content. The prominent component, κ1, was treated with chymosin; the caseinomacropeptide and para κ-casein were separated from the digest and analysed. Starchgel electrophoresis at alkaline pH showed no polymorphism of αs1-, β- and κ-caseins in 170 individual buffalo whole casein samples. On 5 occasions the electrophoretic pattern of αs2-casein suggested genetic polymorphism. The behaviour of buffalo αs1−and αs2-caseins in the presence of Ca2+ was also studied.

Bovine milk-fat globule membrane (MFGM) has been fractionated in to 3 membrane components by isopycnic sucrose density gradient centrifugation. The 3 components, designated as heavy, medium and light material, were characterized by particular polypeptide, lipid, carbohydrate and enzyme compositions.

The heavy material (density > 1·145 g/ml) was red-brown in appearance and consisted of 63% protein, 32% lipid and 5% carbohydrate. The lipid moiety contained 40% triglyceride and 60% phospholipid, while the protein consisted of 3 major polypeptides (apparent mol. wt 135000, 70000 and 53000) in the ratio of 3:6:1. This membrane class was also characterized by the presence of both xanthine oxidase and acid phosphatase. The medium density material (density 1·055–1·145 g/ml) was light red to pink in colour and consisted of 35% protein, 58% lipid and 6% carbohydrate. The lipid contained 45% triglyceride and 55% phospholipid, with nearly 70% of the original MFGM phospholipid being found in this material. The ratio of the 3 major polypeptide bands was 2:4:4 and high levels of both alkaline phosphatase and 5'-nucleotidase were present. The light material (density < 1·055 g/ml) was white to pale pink in colour and was composed of 88% lipid of which 94% was triglyceride, together with 8% protein and 4% carbohydrate. There were virtually no enzymes present and 70% of the protein consisted of a polypeptide with apparent mol. wt of 53000. The 3 membrane classes also differed in carbohydrate content and in the fatty acid composition of their triglycerides.

The morphology, protein and glycoprotein composition, amino-acid analysis, phospholipid and carbohydrate contents and 3 phosphoesterase activities of the milk-fat globule membranes were studied in 4 cows during their whole period of lactation. No differences were found in the morphology and the overall chemical composition. However, glycoprotein composition varied with the cow and, for each cow, with the stage of lactation. The differences were more marked for membranes obtained from colostrum. Acid phosphomonoesterase was practically unchanged during the whole period of lactation, while alkaline phosphomonoesterase and phosphodiesterase increased as lactation proceeded.

Bovine milk-fat globule membrane was solubilized with a zwitterionic surfactant and subjected to chromatography on agarose, with the surfactant in the eluant. Fractions were tested for their effects on the oxidation of buffered linoleate. The maximum oxidative capability was greatly enhanced by the addition of Cu, and became associated with the phospholipids.

Further chromatography of the retarded protein peak from agarose on Sephadex G-200, again in the presence of surfactant, gave 2 protein peaks. Oxidative effectiveness resided almost entirely in the first peak, which was devoid of phospholipid, but high in xanthine oxidase activity. This fraction was subjected to isoelectric focusing, and the xanthine oxidase from this was highly pro-oxidative. Furthermore, its oxidative capability was almost doubled on heat treatment.

Differential scanning calorimetry (DSC) was used to study thermal transitions of the following whey proteins and enzymes in milk ultrafiltrate solution: β-lactoglobulin, α-lactalbumin, serum albumin, γ-globulin, apo- and Fe-lactoferrin, lysozyme, ribonuclease, α-chymotrypsin and xanthine oxidase. Denaturation enthalpies (ΔHD), denaturation temperatures (TD) and the half width of the denaturation peaks in DSC thermograms (ΔT½D) were determined and the degree of renaturation was estimated by rescanning previously denatured samples. A fair correlation between the results obtained by DSC and other more classical methods was found in general. However, for some proteins (α-lactalbumin, lysozyme, ribonuclease and xanthine oxidase), which have so far been considered relatively thermostable, calorimetry reveals conformational changes starting at temperatures as low as about 45 °C. In these cases thermostability observed after heat treatment of milk should be interpreted in terms of renaturation and not of high temperatures of denaturation.

Three cationic materials markedly reduced the rennet clotting time of casein micelle suspensions, the efficacy of each being primarily dependent on the charge and the amount absorbed by the micelles. The reduction in coagulation time was unaffected by components of the milk serum other than salts. No enzymic action by lysozyme on casein micelles was detected. All materials acted by the same mechanism, increasing the affinity of rennet for the micelles and accelerating the aggregation phase. Coagulation did not occur until a minimum amount of κ-casein had been hydrolysed to para-κ-casein. All additives increased the proportion of added rennet retained by the casein in the coagulum. The results indicated that coagulation occurs by specific interactions between micelles modified by rennet.

The specificity of chymosin on αs1-casein was shown to be dependent on the reaction pH and on the state of aggregation of the substrate. In aqueous solution αs1-casein was optimally hydrolysed to αs1-I at pH 5·8; if the casein was solubilized in the isoelectric region by the use of 5 M-urea, optimum proteolysis occurred at pH 2·8. Hydrolysis of αs1-I to yield αs1-II, αs1-III and αs1-IV occurred at pH values > 5·8 in the presence or absence of urea. In the isoelectric region αs1-II, αs1-III and αs1-IV were not formed in the absence of urea where the substrate was aggregated: instead a peptide αs1-V was produced; at the same pH and using urea as a solubilizing agent αs1-II, αs1-III and αs1-IV were formed together with a further peptide αs1-VI.

A method for lactose hydrolysis in sterile milk or whey with Saccharomyces lactis lactase is described. The properties and stability of this enzyme are very favourable for use in milk and neutral whey. The long shelf life of sterilized milk and whey products is utilized for a prolonged incubation time – one to several weeks – at room temperature. Thus, minimal amounts of enzyme are needed which makes enzyme costs very low.

The nutritional protein quality of lactose-hydrolysed milk after some industrial processes was studied with N balance experiments on growing rats.

Ultra-high-temperature sterilization and evaporation at 25 °C did not influence the nutritional value significantly, whereas spray-drying under conditions usually used for ordinary milk gave a considerable reduction in protein quality. This was caused mainly or entirely by loss of biologically availabe lysine.

Confirmation was obtained for the occurrence of an interaction between high and low molecular weight fractions of milk during its pasteurization, resulting in the formation of germinant(s) for Bacillus cereus. Various milk fractions were added to supernatants or dialysates of raw skim-milk, pasteurized and assayed for germinant. Micellar casein obtained by high speed centrifugation of raw milk stimulated germinant formation, but whole casein obtained by acid precipitation was less stimulatory and individual casein fractions showed no stimulation. A membrane rich ‘fluff’ layer obtained by high speed centrifugation of raw milk was highly stimulatory and suggested the possibility that the somatic cell count of milk may be related to germinant production.

Using milk from endotoxin infused and infected quarters of individual cows, a correlation between cell count and germinant formation was clearly demonstrated. Adjustment of the cell counts of individual milk samples was generally accompanied by corresponding changes in germinant formation, though removal of cells by filtration did not have this effect, possibly since germinant precursor had leached from the cells and remained in the milk. Pasteurization was necessary, not simply to express germinant from cells but to effect an interaction of germinant precursors. It is not clear whether the cell associated germinant precursor is derived from the cells themselves or from a related component. Addition of blood serum proteins was without stimulatory effect.

Since low cell count milks sometimes supported appreciable germination after pasteurization, but showed still higher levels when the cell count was raised, germinant may be formed via 2 pasteurization dependent processes, one between milk constituents alone and the other involving both milk constituents and somatic cells.

Several factors which influence the shape of activation curves relating the degree of agitation-induced lipolysis in raw milk to the temperature of agitation were investigated. Curves of the type previously reported (Fitz-Gerald, 1974) containing a maximum at 12–15 °C resulted from low speed agitation with incorporation of air, with fresh (< 12-h old) milk, with milk of fat content ≥ 3·0 % approx. and by low temperature incubation of activated milks. Activation curves containing no distinct maximum at 12–15 °C were obtained from high speed agitation and homogenization, with milks of low fat contents and with aged (≥ 24-h old) milk. Agitation at low temperatures resulted in a maximum degree of activation in fresh milk after 2–4 h cold storage.

During agitation of raw milk redistribution of lipase activity between the cream and skim-milk phases occurred. The extent of redistribution depended on the time and temperature of agitation. Cream prepared from milk agitated at low temperatures contained lipase activity several times greater than cream from unactivated milk. The practical significance of this effect is discussed.