1. The addition of 1 µg. menadione/ml. to milk had no effect on the souring of the milk at 37° C. With higher concentrations of menadione the effect on the keeping quality at 37° C. varied with different milks. In some milks the clot-on-boiling stage was delayed by 1 hr. with 10 µg. menadione and by 2 to over 5 hr. with different milks containing 100 µg. menadione per ml. Some milks, however, showed no alteration in the keeping quality at 37° C. with as much as 1000 µg. menadione/ml.

2. The response of individual milks to the presence of menadione appeared to be related largely to the bacterial flora of the milk, The relative insensitivity of Gram negative rods, including coliform bacteria and of enterococci, to menadione was confirmed. Milks containing large numbers of coliform bacteria showed the least and those free of such bacteria the greatest response to menadione.

3. Menadione fed to milking cows at the rate of 100 mg·/day for a period of 3 weeks had no effect on the keeping quality of the milk when it was held at 37, 22 or 15·5° C. The time of incubation required for the milk to attain a titratable acidity equivalent to 2 ml. N/9-NaOH, to become unstable to 68 % alcohol or to boiling showed no difference between the milk from the cows given menadione and that from the control cows.

4. The menadione had no demonstrable effect on the appetite or the well-being of the cows nor on their milk yield.

5. When as much as 100 μg. menadione was given per cow per day, no menadione was detected in the milk under conditions suitable for the detection of 1 μg. menadione/ml.milk.

The freshly formed surface of milk or cream obtained by overflowing in a double funnel is nearly free from microscopically visible fat.

When this surface is disturbed, either by repeated touching with a platinum ring or by allowing air bubbles to burst there, the fat globules and clumps are brought on to the surface, appearing there as such, or being stretched to lenses, or being spread as patches.

The amount of fat brought onto the surface increases with the extent of disturbance, viz. the number of touches with a platinum ring or the number of air bubbles burst, and with the fat percentage of cream.

Ageing of milk or cream slightly promotes the transfer of fat globules onto the surface.

At 30° C. the bursting of about 10–15 air bubbles is enough to cover the milk surface in the overflow outfit with an almost continuous fat blanket, while at 20° C. the globules and clumps occur separately.

The fat globules rendered hydrophobic by mechanical treatment of the milk surface, as well as the fat patches on the surface, are likely to be accessible to the action of lipase. This may explain the agitation activation of lipolysis in raw milk during certain stages in machine milking and during transportation.

The theory of the scattering of light in colloidal solutions is considered. As a result it is suggested that the reflectance changes in milk which involve a rise or fall in the general level of reflectance are caused by an increase or decrease in the mean size of the colloidal particles. Whether the particles responsible are the casein micelles or the soluble protein depends on the phenomenon to be explained.

The change in reflectance on the browning of milk, which is dependent on wavelength, is considered to have a more complex cause, involving the production of absorbing molecules.

1. A study of the compositional factors which affect the heat coagulation of milk has been undertaken.

2. Calcium-ion concentration and colloidal phosphate content appear to be the chief factors determining the tendency of a milk to coagulate on heating.

3. Acidity (mainly derived from thermal decomposition of lactose and casein) and heat denaturation of casein are supplementary coagulation factors which develop during the heating process.

4. Lactose, as the main source of heat-developed acidity, is an important secondary factor in heat coagulation, but not an essential one. Coagulation can proceed, though more slowly, in its absence. The serum proteins play no part in the phenomenon.

5. A provisional theory of the heat coagulation of milk based on these findings is put forward.

The fat globules in milk and cream by taking up the fluorescent dye phosphine from aqueous solution are rendered fluorescent, and show under the blue light fluorescence microscope a bright yellowish green coloration against the black background. Even very small fat globules (in homogenized milk, cream, skim milk, or buttermilk) and very thin fat layers on the milk-air boundary or on glass can be distinguished owing to the high contrast.

By using glycerol containing two fluorochromes, phosphine for the fat and basic fuchsin for the proteinaceous matter, a very sharp differentiation of these two components in milk-powder particles is attained. Differences in the state of dispersion of fat caused by manufacturing technique and storage conditions, and affecting the properties of powders, are clearly made visible.

The Gerber method (B.S. 696:1936) and the Röse Gottlieb method (B.S. 1741:1951) for the determination of the fat content of milk have been compared on 208 samples of milk covering the range of 2·5–6·0% fat. The following relationship was found between the Gerber percentage (G) and the Röse Gottlieb percentage (RG):G = 1·036 RG – 0·097. Thus, for milks containing 3·0, 4·0, 5·0 and 6·0% fat, as determined by the gravimetric Röse Gottlieb method, the Gerber test gave results which were higher, on the average, by 0·01, 0·05, 0·08 and 0·12% fat respectively.

If the capacity of the Gerber milk pipette were reduced from 11·04 ml. of water, as specified at present, to 10·94 ml., the average results obtained by the two methods would be in agreement for milks with a fat content around 3·6%, the average for milk in England and Wales, and the difference between the results by the two methods would, for most purposes, be negligible over the normal range of fat content.

Tables are given, for the 11·04 and 10·94 ml. milk pipettes, showing the average differences between the results by the two methods for various values of Gerber fat percentage.

The density of raw milk between 10 and 45°C. has been examined. The effect of composition on the expansion of raw milk has been studied and the variation of the densitytemperature coefficient quoted for different values of milk composition.

The contributions of lactose and chloride to the total freezing-point depression of milk have been measured by an incremental procedure. Successive additions of these substances to watered milk have enabled direct determination of the partial freezing-point depression to be made in a medium substantially the same as the original.

In previous work the browning reaction in milk was examined by measuring the fall in optical reflectance which occurred during browning. It was then found that the heating of milk caused an initial rise in its reflectance, and, in the present paper this rise in reflectance, or whitening of milk, is examined in more detail. It is shown that the reaction causing it is independent of the subsequent browning. Whitening occurs at temperatures above 60°C., and takes place more rapidly at higher temperatures. The curves of reflectance against time are not exponential, and there is some evidence that the maximum amount of whitening depends on the temperature at which the milk is held. Reduction in pH of the milk causes an increase in the amount of whitening for a particular time-temperature treatment. From these data and other experiments it is concluded that the rise in reflectance is brought about by the denaturation of the soluble proteins of the milk and their subsequent coagulation into particles large enought to reflect light.

1. The problem of unsatisfactory curd formation in cottage-cheese manufacture has been studied in relation to milk composition.

2. Addition of calcium chloride to the milk did not produce significant improvement.

3. There was a distinct breed difference in the curd formation; Jersey milk produced satisfactory curd whilst Friesian milk invariably produced unsatisfactory curd.

4. Dilution of Jersey milk to the same level of precipitable casein as Friesian milk resulted in unsatisfactory curd.

5. The presence of 10 % Friesian milk in Jersey milk rendered the latter unsatisfactory.

6. The Walker formol titration for determination of casein gave significantly high values with Friesian milk. This is attributed to the different distribution of nitrogen in Friesian milk.

The effect of natural variations in the pH, and in the casein, soluble-protein and lactose contents on the whitening and browning of separated milk has been studied by holding samples of known composition, obtained from individual cows, at a temperature of 110°C. for various times and determining their reflectances after treatment.

The rate of browning, measured as a rate of loss of reflectance at a wave-length of 4260 Å., was found to depend on the pH of the milk. Apparent variations of the rate of browning with protein content are considered to have been caused by associated variations of pH with protein content in the milk from the different cows. The rate of browning varied over a range of 2:1 for the samples examined.

The whitening of milk, measured as the maximum rise of reflectance occurring on heating, was found to be much more variable, and over the same range of samples varied by 5·5:1. The soluble-protein content and pH affect the amount of whitening, but there appears to be some other factor of importance which was not covered by the chemical analyses that were made.

A considerable range of reflectances is shown by different milk samples after a fixed heat treatment. These differences are determined more by variations in the amount of whitening than by variations in the rate of browning.

1. Steam distillates containing the flavouring substance(s) from Cheddar cheese were examined chemically. After the volatile fatty acids had been removed, the only substances identified in the flavour concentrates were ethanol, butyraldehyde, ethyl acetate and ethyl butyrate. None of these compounds appeared to be connected with the cheese flavour.

2. The essential flavour compound(s) could not be identified but some of its properties were elucidated.

3. The findings of other workers that the lower volatile fatty acids, diacetyl and acetyl methyl carbinol contribute to Cheddar-cheese flavour could not be confirmed. Flavour tests with numerous other compounds failed to show that they contributed to the typical flavour of Cheddar cheese.

The author gratefully acknowledges the helpful criticism and advice of Dr H. R. White-head throughout the investigation.

The C6–C11 2,4–dienals have been identified in distillates from skim milk with oxidized flavour. The C4–C11 2–enals were isolated from the same distillates in a previous investigation. The most abundant individual compounds in the two groups were 2–octenal, 2–nonenal, 2–4–heptadienal and 2,4–nonadienal. These compounds when flavour–tested in skim milk in dilutions of 10–7–10–9 closely resembled oxidized (cardboard) flavour. It is concluded that they are the main constituents of this flavour defect and that they originate from the oxidation of the more highly unsaturated fatty acids in milk lipids.

Using chromatographic techniques, a number of compounds was isolated from the steam distillates of skim milk containing oxidized (cardboard) flavour. The following compounds were definitely identified: acetone, acetaldehyde, n–hexanal, crotonaldehyde, and the C5 to C11 2-unsaturated aldehydes. Presumptive evidence for the presence of several 2,4-diunsaturated aldehydes of medium chain length was obtained also. Acetaldehyde and acetone were also isolated from normal skim milk; these two compounds appear to play no part in the defect.

2-Enals, in particular the C8 and C9, were considered to be the principal flavour-determining compounds. In milk at dilutions of 1 part in 107 to 109 they impart an oxidized type of flavour resembling that known as cardboard. Evidence was obtained that 2,4-dienals were also present and they produced a similar flavour.

It may further be deduced that cardboard flavour in milk is caused by the preferential oxidation of di- and polyunsaturated fatty acids.

Butterfat oxidation occurred in both salted and unsalted butters during storage at 14° F. Butterfat oxidation values, after storage, were much lower in unsalted and in highly salted butters than in butters of normal salt content.

Butterfat oxidation in salted butters during storage was retarded by treatment with antioxidants. These included fat-soluble and water-soluble substances, surface-active agents and copper-complexing compounds.

Unsalted butter, salted butter and salted butter treated with antioxidants all developed ‘storage’ flavour during storage for eight months.

Many of the antioxidants added to salted butter were effective in retarding further fat oxidation and further increase in intensity of storage flavour when the butters were transferred to a temperature of 60–65° F. after storage.

Quantitative data have been obtained concerning the amounts of individual amino-acids present in the aqueous phase of Cheddar cheese during the ripening process. They differed from the amounts found in casein by the larger amounts of basic amino-acids, smaller quantities of proline and the presence of ornithine.

Tasting tests showed that amino-acids contribute an important background flavour to Cheddar cheese.

An unidentified substance or group of substances, representing 7–9% of the total ninhydrin-positive material in the serum of ripe cheese, has been observed.

The author gratefully acknowledges the interest and advice of Dr N. J. Berridge, and the technical assistance of Mrs K. Kelly. Thanks are also due to Miss H. R. Chapman for making the cheese.

1. Detailed analyses for the major constituents of the colostrum and milk of four sows are reported. In all cases the initial colostrum is characterized by a very high protein, and a low lactose and fat content. As with the colostrum of other species, the transition to milk occurs progressively during the course of about 4–7 days.

2. Analyses for mineral constituents, calcium, magnesium, phosphorus and chloride are reported on a range of samples covering the whole lactation of two sows. In contrast to the ash of the colostrum of most other species, the ash of the colostrum of the sow is lower than that of normal milk, and as lactation is established there is a rise in the total ash content, and in its main constituents, calcium and phosphorus.

Cheese has been successfully made from raw and pasteurized milk by a process similar to that employed for Cheddar or Cheshire-type cheese but omitting the starter inoculum.

In the preferred method gluconic acid lactone was used as the acidifying agent during the setting of the curd and after milling.

The flavour of the best products was acceptable to a number of people not necessarily experienced in cheese-tasting, but it was different from that of normal Cheddar.

No improvement in flavour was achieved by inoculation of the cheese milk with a strain of L. casei and L. brevis.

Further detailed investigation is needed to perfect the process and to determine whether its use in industry is justified or desirable.

The detailed composition of samples of milk from three blue whales (Balaenoptera sibbaldi) is reported in terms of total solids, fat, solids-not-fat, total protein, casein, soluble proteins, non-protein nitrogen, lactose, chloride, ash, calcium, phosphorus, sodium, potassium, magnesium, vitamin A, thiamine, biotin, riboflavin, nicotinic acid, vitamin B6, pantothenic acid and vitamin B12.

The composition of the milk of the whale is compared with that of other species.