The volatile components of milk have been isolated in a form suitable for application to a gas chromatograph, using the simple rapid technique of entraining them in a gas stream and trapping in a syringe barrel cooled in liquid nitrogen.

The souring process in milk which occurred during incubation at 22 °C was followed by observing the differences between chromatograms of samples taken at intervals. Onset of souring was detected with a sensitivity similar to that obtained by measurement of pH, but the chromatographic method had the advantage of being independent of the initial pH and buffering power of the milk.

With suitable chromatographic apparatus the total analysis time including the preparation of the sample could be about 3 min. Modifications are discussed which would increase the speed of analysis, and thus form a basis for the development of a practical method of assessing the odour of milk before processing.

The lipid content of short rotation ryegrass at two stages of growth was followed at weekly intervals for several months in two spring-early summer seasons. Short succulent ryegrass consisting entirely of leaf tissue contained more lipid (mean, 8·1% of the dry weight) than mature ryegrass which contained appreciable stalk (mean, 5·1% of the dry weight). The lipid from the new growth contained fatty acids with appreciably higher proportions of linolenic acid, which was balanced mainly by lower proportions of linoleic and palmitic acids.

When monozygotic twin milking cows were grazed on the short rotation ryegrass grown to two stages of maturity, it was found that the fatty acid composition of the milk fat from the two groups was different. The milk fat of cows grazed on the new growth contained higher proportions of oleic acid and other C18 acids, whilst the proportions of myristic and palmitic acids were lower. The total proportions of the short-chain fatty acids were not greatly different, although in the group on new growth butyric acid was present in higher proportions and hexanoic and octanoic acids in lower proportions. The higher unsaturation of the fatty acids in the milk fat of this group of cows may be related to the higher levels of unsaturated fatty acids in the young ryegrass diet and to the extent to which these unsaturated fatty acids are hydrogenated in the rumen.

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.

Cheeses collected monthly for 6 months from 6 factories in the same district were stored for a period of 12 months. At intervals the cheeses were sampled and the fats extracted for oxidation tests. There was no increase in peroxide value, no decrease in induction period and only a slight increase in free fat acidity during storage of the cheeses.

The effects of changes in the conditions of preparation on the composition of the k-casein complex have been studied and a method of preparation is suggested which embodies the optimal conditions. The varied conditions include temperature of precipitation of the acid casein, the pH, temperature, CaCl2 concentration and duration of the CaCl2 treatment, and the conditions of centrifuging. Changes in composition caused by alcohol fractionation are reported and the results are discussed from the point of view of k-casein as a complex of three or more proteins.

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.

When k-casein was treated with rennin at neutral pH all the sialic acid contained in the protein was found in the glycopeptide released by the enzyme. From the known molecular weight of the glycopeptide and its proportion in k -casein, a molecular weight of the order of 50000 was calculated for the protein

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.

An apparatus is described which measures at 10—15 sec intervals the viscosity of rennetted milk taken from a cheese vat. The first signs of an increase in this viscosity mark what is at present the earliest measurable stage in the process of coagulation. Coagulation times so determined agreed fairly closely with the observations of a skilled cheese-maker and, for a given milk, were inversely proportional to rennet concentration over quite a wide range. Clotting times obtained by the method of Berridge (1952) for standardizing rennets came 2 or 3 min after those determined by the new method and were linearly related but not proportional to inverse rennet concentration.

The bulked milk from a flock of Awassi sheep was analysed in two successive seasons. In the second season a wider range of analyses of samples taken from the time the first few ewes came into milk until almost the end of the production season (minimum and maximum numbers in milk 8 and 199) gave the following average values: specific gravity, 1·0366; titratable acidity, 0·217%; pH, 6·65; fat, 6·88%; protein, 6·18%; lactose, 5·75%; solids-not-fat, 12·99%; ash, 0·928%; CaO, 0·29%; p2O5, 0·32%; CaO in ash, 31·5%; P2O5 in ash, 34·3%.

The results are compared with the published compositional figures for sheep's and cow's milks.

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.

The numbers and types of non-starter lactic acid bacteria, lipolytic bacteria and group D streptococci in cheese milks and corresponding Cheddar cheeses have been studied and their relationship to cheese flavour discussed. Different milks, heat-treatments and starters were used, and their association with flavour investigated. The pH and fat, salt and moisture contents of the cheeses were also determined.

The non-starter lactic acid flora consisted mainly of Lactobacillus casei, L. plantarum, L. brevis, L. buchnerii, Pediococcus spp. and Leuconostoc spp. Lactobacillus casei was nearly always present in the milks and cheeses, predominating in most of the cheeses, particularly in those made from milk which received the most severe of the three heat-treatments tested (160°F for 17 sec). Leuconostocs were not found in any of the cheeses. Other species sometimes occurred in approximately equal numbers to L. casei, particularly in cheeses manufactured from the milder heattreated milks. Cheeses made from milk receiving the highest heat-treatment contained fewest bacteria and scored lowest for flavour. The average flavour scores increased as the number of species contributing to the non-starter lactic acid flora at the time of tasting increased.

The lipolytic organisms capable of hydrolysing butterfat consisted mainly of Gram-positive cocci, predominantly Staphylococcus saprophyticus. The group D streptococci occurred infrequently, Streptococcus faecium being the most commonly occurring species.

A definite correlation was found to exist between the starters used and the flavour of the cheeses. The pH of the cheeses was associated with the flavour, but the fat, moisture and salt contents of the cheeses showed no definite effect.

In a series of 3 trials there was little or no difference in milk yield when cows were fed the same quantity of dry matter in the form of well-preserved hay or silage from the same sward.

A higher milk yield was obtained from silage made from grass at an early stage of maturity than from silage or hay made from the same crop 5 weeks later.

In 2 trials when hay or silage was fed ad lib. the dry-matter intakes of the cows were higher with hay than with silage, and there was a consequent increase in milk yield and S.N.F. content in favour of hay.

Some of the results indicated that with certain silages a depression in the S.N.F. content of the milk, due to a decrease in the casein content, could occur, although this was not associated with an inadequate energy intake.

Dissolved oxygen in anhydrous milk fat is reacted with an aqueous manganous-ferrous hydroxide suspension at 50 °C. The mixture is acidified and after separation into two layers the amount of ferric iron in the aqueous layer is estimated by iodometric titration. The procedure is relatively simple and is suitable for routine testing of milk fat.

A method is described for the preparation of k -casein and for its purification by chromatography on DEAE cellulose. The conditions of preparation have been chosen so as to avoid drastic alteration of the k -casein and permit the isolation in relatively pure form of one-half to two-thirds of the amount theoretically available.

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.

The effect of the level of pre-partum feeding of Friesian heifers on the yields and composition of the milk in the subsequent lactation has been investigated using 23 heifers on each of 2 treatments. For 1 treatment, over a period of 6 weeks before calving, generous grazing on good pasture was supplemented with 8 lb/cow daily of concentrates, and for the other only restricted grazing of an already sparse sward was allowed.

For the period 3—8 weeks from calving the heifers fed at the high plane pre-partum produced significantly more milk than those fed at the low plane (36·8 compared with 31·9 lb/cow daily). The solids-not-fat (S.N.F.) and fat contents of their milk were also significantly higher (8·71 compared with 8·47%, and 3·72 compared with 3·38%, respectively). For the period 3—14 weeks from calving the effect of milk yield was slightly greater but the effect on composition was less. For the period 3—30 weeks from calving the difference in milk yield remained significant (31·3 compared with 26·1 lb/cow daily), but the average differences in S.N.F. and fat contents over this period (8·63 compared with 8·51%, and 3·75 compared with 3·59%, respectively) were not significant.

The heifers fed at the higher plane increased in liveweight before calving at a rate which was highly significantly greater than that of the heifers fed at the low plane. After calving, the heifers which had been on the higher plane remained almost constant in weight during the first 12 weeks whilst the others regained some of their losses, a difference which was highly significant. This recovery was apparently made at the expense of milk yield and composition.