A complete range of methyl ketones with odd numbers of carbon atoms from C3 to C15 was isolated by steam distillation at atmospheric pressure from fresh butter-oil, cream and Cheddar cheeses of various ages. Evidence was produced to show that the greater part of these methyl ketones was formed during the heat treatment of milk fat. The maximum quantities of methyl ketones obtainable from butter-oil, determined by exhaustive steam distillation at atmospheric pressure, averaged from 14 ppm. for undecan-2-one to 46 ppm. for pentadecan-2-one. Some artifact formation of methyl ketones also occurred, although to much less extent, when dairy products containing milk fat were steam distilled under reduced pressure at 40 °C. Possible mechanisms of formation of the methyl ketones are discussed.

Since it proved possible to extract methyl ketones in low concentration from mature cheese at room temperature, it is evident that milk fat may contain precursors which break down to methyl ketones slowly during cheese ripening, this breakdown being accelerated at higher temperatures. Methyl ketones may therefore play a part in Cheddar flavour, but a previous report from this Institute that the time of first appearance of certain methyl ketones of odd numbers of carbon atoms above C5 in steam distillates, at atmospheric pressure from Cheddar cheese, coincided with the appearance of the typical Cheddar flavour was not confirmed.

The accuracy of methods that utilize the colour-forming reaction between pyridine, acetic anhydride and citric acid for the determination of citric acid in milk and milk sera has been examined. A method based on that of Saffran & Denstedt (1948), in which a trichloroacetic acid (TCA) filtrate is used, gave values 3–5% low for the citric acid content of both milk and milk ultrafiltrate. The method of Merier & Boulet (1958), in which aqueous samples are analysed, gave an accurate value for the citric acid content of milk. The same technique but applied to aqueous-NaOH samples (Marier & Boulet, 1960) gave values about 7% high for the citric acid content of milk and about 3% high for the citric acid content of ultrafiltrate. However, a method using the technique of Marier & Boulet and TCA filtrate gave accurate values for the citric acid content of both milk and milk ultrafiltrate.

A study was made of the machine milking rates of a sample of Jersey cows comprising daughter-dam pair groups, obtained from thirteen New Zealand herds during mid-lactation.

Twenty-one per cent of the variation in maximum rate of flow occurred within herds and the remainder between herds. Differences in the type of preparation of cows for milking did not have a significant effect on the average milking rates for herds. The variance in milking time between cows within poorly prepared herds was greater, however, than that in the better prepared herds.

Heritability estimates for maximum rate of flow, derived from the regression of daughters' records on dams' records, were found to be of the order of 80%.

In an earlier paper, one of us (Oosthuizen, 1962) showed that vegetable rennets produce a fall in the viscosity of sodium caseinate solutions which follows the equation of first-order chemical kinetics; but that the proteolysis involved is stronger than that of calf's rennet since the vegetable rennets attack a greater proportion of the casein ensemble.

To investigate the effect of replacing part of the concentrates by roots, a 16-week winter-feeding experiment was made using twelve Ayrshire cows. All the cows received 8 lb of hay per day and enough grass silage for a measurable residue to be left at each feed. Two rations were supplemented with 45 lb of fodder-beet per day but the other two contained no roots. At each level of root feeding, concentrates were fed at either 3·50 or 1·75 lb per 10 lb of milk.

All the fodder-beet was eaten (8·4 lb dry matter) and, as this caused a reduction in the intake of silage dry matter of only 3·4 lb per day, there was a net increase in drymatter intake. The level of concentrate feeding had little effect on the intake of the other feeds. Rations which included roots contained significantly less crude fibre than rations without roots.

The mean daily milk yields for the treatments with the low and high concentrate levels were 29·5 and 33·9 lb, respectively, without roots and 31·8 and 35·8 lb with roots. The fat percentages of the milk were similar on all four treatments whereas the solids-not-fat (S.N.F.) increased significantly from 8·42% on the treatment without roots and low concentrates to 8·64% on the treatment with roots and high concentrates. The response per 1 lb of extra S.E. was 1·0 lb milk and 0·02% S.N.F. between the low and high concentrate treatments and 0·7 lb milk and 0·05% S.N.F. between the two root treatments. The analysis of milk from individual quarters of all the cows during each period showed the continuous presence of some subclinical mastitis. It was estimated that this lowered the general level of S.N.F. percentage by 0·2% but did not bias the results from any one feeding treatment. For milk from healthy quarters only, the response to 1 lb extra S.E. from concentrates was 0·03% S.N.F. and from beet it was 0·08% S.N.F.

To investigate whether milk of abnormal quality from some quarters of twelve cows on a Latin square type feeding trial would bias the results for chemical composition, the compositions of milk from normal and affected quarters were compared with each other and with that of the milk obtained from the whole udder by normal milking.

The average number of quarters producing abnormal milk in each of the four periods was eighteen, with only small variation between periods. Cell counts ranged from 50000 to 25 × 106/ml with 31% of them below 500000/ml; as cell count increased, lactose percentage and casein number fell. Pathogenic bacteria were detected in only 70% of the abnormal milks. The solids-not-fat (S.N.F.) percentage of milk from affected quarters was lower on average than that from healthy quarters by 0·43, the decrease resulting entirely from a lowered lactose percentage. The total nitrogen content was the same in both types of milk, but there was 4·5% less casein in milks from affected quarters.

Because in this particular experiment the distribution of the abnormal milks was almost uniform over the four feeding treatments, the results obtained for treatment effect on milk composition by the normal milking method were not biased by the occurrence of disease, but the general level of composition was depressed by 0·2% fat and 0·2% S.N.F. In other experiments the incidence of disease might happen by chance to differ between treatments, with the result that the findings about milk composition could be erroneous.

Goat's milk heated at temperatures in the range 94—120 °C underwent the same colour changes as previously found for cow's milk, i.e. whitening followed by browning. The rate of browning varied with temperature according to Arrhenius's Law, and had a Q10 between 95 and 120 °C of 2·6—2·7. This is slightly lower than the value found for cow's milk. It was difficult to produce whitening curves for milk heated at 75—100 °C because of unexplained reflectance variations. It appeared that the amount of whitening which could be produced became less as the interval after milking increased.

Changes in dried skim-milk and in lactose-casein in the ‘dry’ state during storage at 45 °C and 75% r.h. have been studied by the determination of free amino-N, ε-amino groups of lysine, galactose, lactulose, tagatose and 1-amino-1-deoxy-2-ketoses, and by the measurement of changes in colour, solubility and ferricyanide reducing power.

In both systems there is initially a close relationship between the formation of 1-amino-1-deoxy-2-ketoses and the decrease in free amino-N. This conforms with an Amadori rearrangement of an initially formed lactose-protein complex. Change in colour is rapid only after there has been a rapid formation of 1-amino-1-deoxy-2-ketoses and a corresponding decrease in free amino-N. This conforms with browning being due to a breakdown of the Amadori rearranged complex.

It is postulated that galactose and tagatose may be formed by both the basecatalysed degradation of lactose and also by breakdown of the Amadori rearranged lactose-protein complex. Lactulose is postulated to be formed only by base-catalysed degradation of lactose.

A modified entrainment method is described for the estimation of microquantities of hydrogen sulphide in cheese. Optimum recovery is only possible if the conditions are very acid, if oxygen is excluded and if appreciable loss by diffusion is avoided by minimizing the surface area of the sample and the time it is exposed to the atmosphere. The reproducibility of determinations from the same cheese was satisfactory.

The concentration of H2S in New Zealand Cheddar cheese curd at hooping was less than 20 μg/100 g but increased after ripening for 1–4 months to an average concentration of 55 μg, thereafter remaining fairly constant. There appeared to be no simple relationship between characteristic Cheddar flavour and H2S concentration.

Immature ovariectomized mice were used to compare the oestrogenic activities of different parts of the same clover plants; to estimate the relative potencies of biochanin A, genistein and diethylstilboestrol; and to compare the effects of different methods of storage on the oestrogenic potency of red clover leaf and petiole. Test materials were incorporated in the diet fed to the mice and the uterine weight response was used to measure oestrogenic activity.

With material harvested at four different times, the leaf or leaf and petiole had the highest activity; small and large stem fractions of the plant were both relatively less active, and blossom and seed head were inactive.

Comparison of successive estimates of the relative potency of isoflavones and diethylstilboestrol indicated that the relative responsiveness to the two types of oestrogen did not remain constant. Thus comparisons of estimates of oestrogenic activity of plant material, obtained in terms of diethylstilboestrol in different experiments, could be invalid.

The potencies of alcohol, acetone and freeze-dried preparations were compared after storage for 18, 115, 212 and 230 days. Of the procedures tested, the most satisfactory was that in which fresh material was placed in 95% alcohol and the liquor and residue dried and stored at room temperature over concentrated sulphuric acid at reduced pressure.

A survey was made of the frequency of β-casein variants in the milk of cows of five major British breeds. Three variants A, B and C differing in electrophoretic mobility were found to occur either singly or in pairs, as expected if each were determined by a single allele. The A variant was the most common and found in all breeds. Ayrshires and Shorthorns produced no other variant, whilst the B variant occurred in Jerseys and, at low frequency, in Guernseys and Friesians. Production of the C variant was restricted to the Guernsey breed in which it occurred at low frequency. The technique of paper electrophoresis, used for β-casein ‘typing’ of some 600 cows, is described in detail.

It has been shown by Hipp, Groves, Custer & McMeekin (1952) that the differential solubility in urea of the casein components of cow's milk can be utilized for preparative purposes. Fractionation is achieved by step-wise dilution of a solution of all the casein components in strong (6·6 molar) urea. In connexion with the work on the three genetically distinct β-caseins discussed in the preceding paper, the need arose to prepare the variants A, B and C from the milk of appropriate homozygotes. This led to the development of the modified procedure described in this note, a procedure more sparing in urea and more effective in the initial isolation of the β-casein fraction than the original method of Hipp et al.