The volatile fatty acids produced during fermentation in the rumen have been shown to vary in their nutritive properties. Armstrong & Blaxter (1957) found that for lipogenesis in the adult sheep the value of the acids increases with increasing chain length. Rook & Balch (1961) showed that the individual acids have characteristically different effects on the synthesis of the various constituents of milk. In consequence the nature of the end products of fermentation must be one factor affecting the utilization of foods for productive purposes.

Results are given for the effect of different ultra-high-temperature milk sterilizing processes on the thiamine, vitamin B6 and vitamin B12 contents of milk. For all the processes examined, the loss of thiamine is negligible, and the losses of vitamins B6 and B12 lie between zero and 35%. Indirect-heating processes appear to cause more loss of vitamin B12 than of vitamin B6, but the reverse is true of directheating processes.

The role of the essential fatty acids, linoleic and arachidonic acids, in human nutrition has been widely studied, particularly with respect to their possible action in preventing arterial disease in adults, e.g. Kinsell (1963). In addition, Hansen, Haggard, Boelsche, Adam & Wiese (1958) have emphasized the importance of linoleic acid in the nutrition of infants. Although milk fat contains only relatively small amounts of linoleic and arachidonic acids, the part played by milk and milk products in contributing essential fatty acids to the human diet has received considerable attention (Combes, Pratt & Wiese, 1962; Kon, 1962; Hansen et al. 1963; Garton, 1964). However, despite the initial dependence of many infants on dried milk as an exogenous source of essential fatty acids the effects of commercial drying processes on the constituents of milk fat have not been much investigated. A comparative study of the fatty acid compositions of raw and dried milk was therefore undertaken.

A C20 multibranched fatty acid earlier isolated from butterfat in trace amounts has been conclusively identified by means of mass and infra-red spectrometry and gas-liquid chromatography as 3,7,11,15-tetramethylhexadecanoic acid.

A strain of Streptomyces albus, presumed to have originated in raw milk, was found in large numbers in a pair of experimental cheeses. The numbers of streptomyces in both cheeses remained constant over the 4-month period of sampling and a comparison of the numbers obtained from cheese dissolved in citrate with and without mechanical aid revealed no differences, suggesting that the streptomyces was present in the conidial state. The heat resistance of mycelium and of conidia was determined at 62·7 °C (145 °F) and 71·7 °C (161 °F). The mycelial cells showed no resistance to either temperature, there being 100% kill after 15 min at 62·7 °C and 17 sec at 71·7 °C. The conidia, however, were very much less affected after 2 h at 62·7 °C, and 3% remained viable even after 30 min at 71·7 °C. Although the strain was found to be proteolytic, lipolytic and saccharolytic, it appeared to be inactive in the cheese, being present in the conidial state.

Microscopical and chemical studies of seaminess in Cheddar cheese revealed that the white lines or seams characteristic of the defect are sections through layers of crystals lying between the milled curd particles. The crystals were identified from their X-ray diffraction pattern and by their refractive index as calcium orthophosphate dihydrate, CaHPO4. 2H2O. On each side of the adjoining curd surfaces in affected cheese there is a zone about 20 μm thick of strongly contracted protein which is almost devoid of crystals.

Adding sodium chloride to cheddared curd increased the quantities of calcium, phosphorus and water released. The increases were proportional to the amount of salt applied within the range 0–2·5 g NaCl per 100 g curd.

The solubility of calcium orthophosphate was found to rise from about 0·0025 M in water to a maximum of 0·008M in 2 M sodium chloride solution.

It is postulated that calcium and phosphate ions released from the curd into the seam crystallize in the form of CaHPO4. 2H2O as the solubility of the compound is lowered by diffusion of salt from the surfaces into the curd particles.

The effects of stage of lactation and of age on milk and composition yield of cows kept under controlled conditions of feeding and management were investigated. Two groups each of 3 Friesian heifers were used: one group (A) was given a daily diet of 18 lb hay and concentrates at the rate of 3·8 lb/10 lb of milk and kept on experiment throughout the first 3 lactations; a second group (B) was given the same amount of hay and a constant daily amount of concentrates of 10·7 lb and was kept on experiment throughout the 1st lactation only.

The total yields of milk and peak yields for the 1st lactation were similar in both groups. In all the cows, fat content was high early and late in lactation and varied little throughout the mid-lactation period. With cows of group A, the content of solids-not-fat declined until about the 5th week of lactation and then remained steady until a marked rise occurred late in lactation. With cows of group B, however, the content of solids-not-fat was at a minimum between the 5th and 10th weeks of lactation and then increased progressively until late lactation when a more marked rise occurred. Lactose content increased rapidly in the first few days of lactation and then remained constant for several months, eventually declining late in lactation. Characteristic changes were also observed in the contents of total protein, and of the various protein fractions, and of the major minerals of milk.

The concentrations of all major constituents in milk secreted from the 2nd–5th months of lactation tended to decrease from lactation to lactation.

The results are discussed in relation to the development of knowledge of the changes in milk composition throughout lactation.

When crude к-casein was precipitated at pH 3 in the presence of 0·4m-NaCl the supernatant contained up to 80% of the total sialic acid but no detectable cystine or cysteine. Two fractions were obtained from this supernatant by chromatography on DEAE cellulose; one containing 4–6% sialic acid and the other only onetenth of this amount.

Most of the sialic acid of the sialic acid-rich fraction was soluble in 12% trichloracetic acid following treatment with rennin. It is suggested that the glycopeptide released by the action of the enzyme on casein originates from this fraction.

A laboratory method is described which it is hoped will be of value in the search for some of the chemical factors in milk which control the formation of deposits on heated surfaces during commercial processing. The method uses an electrically heated platinum wire as the surface on which deposits are formed under controlled heat transfer conditions. Preliminary results are given on the effect of milk pH on deposit formation, differences in the sensitivity to deposit formation of different bulk milk supplies, and the effect of forewarming on the reduction of deposition.

Similar, marked variations in the freezing-point depressions of jugularvenous blood and of milk throughout a day were observed in cows when drinkingwater was offered for a single, short period each day. Values for milk were found to agree more closely, however, with those for mammary-venous blood than with those for jugular-venous blood. It appears that milk is in osmotic equilibrium with the blood flowing through the udder continuously throughout the period the milk remains within the udder and not only during its formation, and that milk secretion causes a slight alteration in the osmotic pressure of fluids within the immediate locality of the mammary gland. Changes in the milk composition that occurred in association with the observed changes in freezing-point depression were consistent with a movement of water into or out of the udder in response to any change in the osmotic pressure of blood.

A method is described by which the microbial flora of a raw milk sample was reconstituted on different occasions. After segregation on selective media into groups consisting of lactic acid bacteria, Gram-negative rods including coli-aerogenes, staphylococci, streptococci, and microbacteria, and propagation by replica plate techniques on optimal media, suspensions of these groups of organisms were then added in approximately the original proportions to 40 gal batches of heated milk of low bacterial count. When this was repeated on 18 different occasions over a period of 11 weeks, the milk flora was found to be almost identical with the original one.