Since Indian law requires curds to be made from heat-treated milk, a means for distinguishing between curds made from raw and from heat-treated milks was sought. Curds contain whey proteins that are partly or completely denatured by heat treatment; the kinetics of the reaction are first order. The concentrations of native whey proteins in raw and heat-treated milks and in curds made from those milks were measured. No difference was found between the concentrations in heattreated milk and in the curds made from it, so that identical values were obtained for the half-life on heating and for the activation energy of denaturation. The acidity and microbial growth occurring during the production of curd did not affect the whey proteins. On electrophoresis, curd from raw milk gave a few whey protein bands, but curd from milk boiled for 10 min gave none, showing complete denaturation of the whey proteins.

Samples of the mammary gland were obtained from heifers, lactating and dry cows by a freeze-clamping technique. Amounts of lactate, pyruvate, malate, ATP, ADP and AMP were determined in the sample extracts and calculated per g fresh weight and per mg DNA. Pyruvate, lactate and AMP amounts showed only minor changes at different stages of lactation, whereas quantities of malate, ATP and ADP were significantly higher in cows giving high milk yields. Pyruvate levels showed seasonal variations parallel to changes in milk composition. NAD: NADH ratios in mammary cytoplasm showed no significant differences between different groups of cattle, whereas ATP: AMP ratios in mammary gland samples were highest in lactating animals.

Low-angle X-ray diffraction techniques have been applied to the study of the structure of the fat-globule membrane of milk and of Cheddar cheese. Membrane was prepared by freeze-thawing, churning and ether extraction, the endproduct of each method being a pellet produced by centrifuging. High-angle and low-angle reflexions from membrane could be related to triglyceride spacings, and low-angle reflexions due to spacings at about 5·5 nm to phospholipid bilayers. Spacings due to triglycerides were observed in mature Cheddar together with spacings that agreed well with values for some of the amino acids.

Aliphatic monocarbonyls have been quantitatively estimated in casein and skim-milk powder during storage. Concurrently these products have been evaluated organoleptically. A close relationship was evident between monocarbonyl level and the flavour or age of the lactic casein. Furthermore, the greater flavour stability of rennet casein and skim-milk powder was coupled with reduced monocarbonyl content. Fractionation of monocarbonyls into classes and individual compounds has shown that the higher levels in lactic casein compared with other low-fat products can be accounted for by a high level of acetone. The absence of appreciable quantities of other odd-numbered methyl ketones suggests that either acetone is derived from a non-lipid constituent of acid casein or decarboxylation of acetoacetate is specifically catalysed at acid pH. All methyl ketones identified in these low-fat dairy products were present in subthreshold concentrations. Saturated and unsaturated aldehydes were present at similar levels in stored lactic casein, rennet casein and skim-milk powder samples irrespective of their degree of musty or stale flavour.

More than 90% of the C2,4,6,8,10 fatty acids and C8,10, δ-lactones added at quantities between 0·5 and 40 ppm were recovered from volatile-free butter oil by cold-finger molecular distillation at 35°C, while approximately 65% of the C12 fatty acid and of the C12 δ-lactone was recovered. Cold-finger molecular distillation at 50°C increased the recovery of the C12 compounds to more than 90%. The acids and lactones were estimated quantitatively as the free compounds by gas chromatography on a mixture of Carbowax 20 M and isophthalic acid as the stationary phase.

A simple in-line milk sampler is described for determining the bacterial contamination from the udders of cows milked in recorder machines. When sterilized, and used with a sterile cluster, it collects a milk sample bacteriologically representative of the cow's total yield and it can be used with minimum disruption of the milking routine.

The nutritional quality of milk treated by 2 previously described processes for the removal of cationic fission products has been evaluated by the use of the baby monkey (Macaca irus).

The first process involves acidification of the milk to pH 5·2–5·3 and, when the treated milk was tested on baby monkeys, it was found to be nutritionally unsatisfactory. This result confirmed those previously obtained with baby pigs, from which it was concluded that the process cannot be recommended for the treatment of milk intended for young babies.

Two resin beds are used in the second process and no acidification is involved. Milk treated by this process was first tested on baby rats and pigs and then on baby monkeys. No change in the nutritional value of the milk was detected and it was concluded that this is the process which should be used if it should ever become necessary to remove fission products from milk intended for young babies.

A method for obtaining distillates from whole Cheddar cheese is described. The distillate has an aroma at −80°C closely resembling that of the cheese before distillation. Gas chromatograms of the distillate were obtained by sampling the vapour over the distillate at −80°C, using both a 15-m Apiezon surface-coated open tubular column and a 1·5-m glass column packed with Porapak Q. The aroma of the effluent was evaluated and the chromatograms simultaneously recorded by passing the vapour through a splitting device before the flame-ionization detector of the gas chromatograph. The compounds responsible for the aromas detected in the effluent were identified using a gas chromatograph directly linked to a mass spectrometer. Of the compounds identified in the distillate, H2S, methanethiol, dimethyl sulphide and diacetyl had the most intense aromas, and these compounds are discussed in relation to their importance to Cheddar-cheese aroma.

The kinetics of the primary phase of rennin action on casein micelles and on total casein prepared by ultracentrifugation have been studied. It was observed that the values of Km and V varied for the different casein samples. Addition of whey proteins to the reaction mixture or variation of the concentrations of Na+ and K+ had no effect on Km and V and V, but there was a consistent increase in the values of both these parameters when κ-casein was added. It was concluded that these changes were due to an increase in the accessibility of the κ-casein resulting from the rearrangement of the casein micelles. These results are in agreement with our earlier conclusion that the Km for rennin action on casein is dependent on the carbohydrate composition of the molecule.

Results are presented demonstrating quality control of the analytical procedures used during the application of metabolic profile tests to dairy herds over a period of 3 years. The significance of analytical variance is discussed in relation to the average population variance in dairy herds.

It is concluded that analytical variance can be restricted to reasonable proportions providing that careful quality control is continuously employed.

Four experiments were carried out with Friesian cows in different stages of lactation to determine the influence of the crude-protein content of the diet on the digestibility and utilization of dietary constituents and on the cow's performance and milk composition.

The rations were composed so that they met the energy requirements of the cows, but crude-protein content was widely variable.

Our findings on the digestibility of the dietary constituents were in agreement with the data given in the literature.

The utilization of dietary N for milk secretion was influenced by the level of N intake only when the crude-protein content of the diet was lower than a limiting value, which varied according to stage of lactation. When this value was not attained the daily milk production was affected, but not the protein content of the milk.

The optimal crude-protein content of the diet was 15–16% (dry-matter basis) when milk production exceeded 20 kg/d, 12–13% for a production of 15–17 kg/d and 11–12% for cows giving less than 10 kg of milk daily.

β-Casein is highly resistant to proteolysis in Cheddar cheese. A decrease in NaCl concentration reduced its resistance, but even in the absence of salt the amount of proteolysis of β-casein was slight. Proteolysis in Cheddar cheese increased when the moisture levels were raised by adding water. The relative susceptibility of β-casein to proteolysis by rennin was reduced considerably when the concentration of a sodium caseinate solution was raised from 10 to 20%. Sequestering the Ca2+ by means of EDTA had no significant effect on proteolysis of β-casein. It would appear that the resistance of β-casein to proteolysis is due to the substrate rather than the enzyme and it is suggested that the reduced relative susceptibility to proteolysis is due to some concentration-dependent physical change in the casein molecule which renders the β-casein inaccessible. The salt concentration would also appear to influence this change.

Cheddar-cheese flavour is largely independent of rennet concentration and it is possible to manufacture cheese of satisfactory quality using half-normal rennet levels.

A technique is described for preparing ultrathin sections from cheese for electron-microscopic examination. The internal structure of fresh Domiati cheese was found to be composed of a framework of large, spherical casein aggregates held by bridges and enclosing fat.

After pickling, the casein aggregates were partly disintegrated into small spherical particles forming a loose structure.

Large differences in new infection rates occurred with half-udder milking machines in which one half of the cluster operated substantially free from vacuum fluctuations while the other half was subjected to various combinations of different types of fluctuation in vacuum. To increase the rate of new infection all teats were contaminated before and after each milking by immersion in a suspension of Streptococcus agalactiae and Str. dysgalactiae. A series of short-duration trials indicated that neither irregular nor cyclic fluctuations in vacuum acting alone were able to increase new infection rate. However, either the Nyhan and Cowhig irregular fluctuation, or a variant of it in combination with cyclic fluctuations in vacuum, was able to do so under the particular experimental conditions used.