All teats of a herd of lactating cows were contaminated after each milking with Staphylococcus aureus. Two teats of each cow were subsequently dipped in an iodine solution, while the remaining 2 teats were not dipped. For cows with a single infection the interval to infection in dipped and undipped quarters was 64 and 60 d respectively, while for the first infected quarter of cows with multiple infections the interval to infection in dipped and undipped quarters was 50 and 39 d respectively. For the second quarter infected in cows with multiple infections, the period between the first and second infection was 21 and 12 d for dipped and undipped quarters respectively. It is suggested that while teat skin disinfection was effective in reducing the rate of new infection, it had little effect on the process of infection in those quarters becoming infected. The occurrence of an infection in one quarter doubled the rate of infection in the other quarters.

The mass flow-rate (FR) of milk from the bovine teat within individual pulsation cycles was measured by continuous computation of the average optical density of the milk–air mixture within a teatcup. Measurements during milking were made on both live and excised teats using a range of teatcup liners, vacuum levels and pulsation characteristics. During a typical pulsation cycle, soon after the start of milking, milk FR from live teats reached a peak within 100 ms of the start of the flow period and fell to about 60% of the maximum value between 0·5 and 1·5 s of flow. If the liner was held open for longer than 1·5 s, the FR typically declined a further 10% over the next 10–15 s. After 10–15 s little or no further change occurred in milk FR at normal milking vacuum levels. Milk flow from excised teats reached a steady value within 100 ms of the start of the flow period and showed no subsequent fall in FR.

Within individual pulsation cycles the changes in FR from live teats are affected by: (i) the degree of compressive load applied by the collapsed liner to the teat in the preceding cycle; and (ii) the duration of application of the compressive load. Increasing the degree of compressive load or the length of time of loading increases the peak milk FR of the next cycle by reducing the degree of congestion in the tissues of the teat surrounding the teat canal. Muscular effects are of secondary importance. The relatively small changes in milk FR associated with muscle contractions of the teat can be seen most clearly at low milking vacuum levels (below about 30 kPa) or with an unsupported teat (e.g. using a very distensible, thin-walled liner).

Subcutaneous injections of 30 mg atropine into lactating cows induced a 20–40% decrease of free amino acid (AA) levels in arterial plasma. Minimum levels were observed after 30–50 min. The decline persisted for more than 6 h. The greatest fall in concentration was noted for tyrosine, methionine, lysine, arginine, phenylalanine and threonine. Arterial glucose levels remained unaffected. The effect of atropine on milk secretion was studied in 2 cows which were milked every hour with the aid of oxytocin. Maximal effects were observed after 3–4 h. They included reduction in concentration of casein and ±-lactalbumin (±-la) and a decline in production of milk (20%), casein (35%), ±-la (45%) and lactose (18%). Uptake by the lactating udder over a period of about 1 h after injection of atropine was studied in 2 cows. Mammary blood flow and glucose uptake remained unaffected. There was a positive correlation between arteriovenous differences of essential AA and arterial plasma concentrations. The uptake of essential AA decreased by approximately 50 %. There was no evidence that atropine has a direct inhibiting effect on the udder. It is suggested that the decrease of ±-la synthesis might induce an inhibition of lactose synthesis and milk production.

The acid-soluble ribonucleotides of cow's, goat's and sheep's milks were measured by enzymic and ion-exchange chromatographic procedures at different stages of lactation. Colostra and milk from ruminant species contained orotic acid and 13 well-identified nucleotides: AMP, CMP, GMP, UMP, UDP, GDP, UDP-glucose, UDP-galactose, UDP-N-acetyl-glucosamine, UDP-N-acetyl-galactosamine, UDP-glucuronate, GDP-mannose and GDP-fucose. Cow's, goat's and sheep's colostrum contained significant amounts of nucleotides, which increased in amount from the moment of parturition, to reach a maximum 24–48 h later. The nucleotide concentration decreased thereafter with advancing lactation. Cow's milk contained substantial amounts of orotic acid, which increased during lactation, whereas in goat's and sheep's milk no increase took place. The cytidine and adenosine derivatives in ruminants' milk did not change significantly during lactation. The UDP-glucose/UDP-galactose ratio was measured in ruminants' milk at different stages of lactation.

Samples of milk from silo tanks were stored at refrigeration temperatures and examined at intervals for pyruvate content and total colony count. Significant relationships between pyruvate, μg/ml, and log colony forming units (cfu)/ml were established for samples stored at 2°C for 2, 3 and 4 d (3, 4 and 5 d of age respectively) but at 5 and 7°C the relationships after 2-d storage (3 d of age) were not significant. From an overall relationship it was predicted that 4 μg pyruvate/ml would correspond to a bacterial content of 3·7 x 106 cfu/ml with 95% confidence limits of 6·6 x 10 cfu/ml. 2·1 x 107 cfu/ml.

The free glucose concentration in the aqueous phase of samples of goat, sheep, cow, rat and rabbit milk was about 0·1–0·3 mn, while that in human milk was about 2 mM. During starvation the glucose concentration of goat milk fell considerably (by about 80 % in 2 d) in parallel with the decreased rate of lactose production. With rats fed ad lib., glucose concentration in the milk was greater at 12.00 h than at 18.00 h, when lactose synthesis has been shown to decrease. 3-O-Methyl-D-glucose injected into the goat mammary gland via the teat canal specifically entered the blood. These findings support the idea that glucose equilibrates across the apical membrane of mammary secretory cells, so that milk glucose concentrations reflect intracellular glucose concentrations.

The frequency distribution of aggregates of casein micelles was determined inelectron micrographs of rennet-treated skim-milk. The average degree of aggregation was constant until after 60% of the coagulation time, then increased linearly to 100% of the coagulation time and subsequently rose more slowly. The observations indicated that the rate of aggregation of casein micelles was determined by the random collision of particles, with no preference for the formation or reaction of aggregates of any particular size. The linking together of micelles was not rate-determining.

Use of a model of the renneting reaction has led to the definition of the amounts of soluble casein present in milks of different concentrations, at the time of clotting. It is shown that, although the clotting time (RCT) is relatively little affected by the concentration of milk by ultrafiltration, the proportion of casein which is soluble at the RCT is highly dependent upon the concentrations of both milk and rennet. This may affect the structure of the curd.

The isotherms for Ca2+ binding to bovine β-casein have been measured at 5 temperatures in the range 4–40 °C and at 4 different ionic strengths. The results are interpreted by an interactive-site binding model, and are compared with results previously obtained on αs1-casein. The affinity of β-cesein for the first Ca2+ to bind is similar to the affinity of αsl-casein for the same binding event: however, binding of subsequent Ca2+ to β-casein is weaker than the binding to αs1-casein. The results are discussed in terms of precipitability of the 2 caseins caused by the binding of Ca2+.

A modegl is proposed for the equilibria between the components of the salts in milk. The model includes complex formation between calcium ions and the various ionized forms of citric, lactic and phosphoric acids, and makes allowance for the effect of ionic strength. A computer program has been written to calculate the pH of the milk salt solutions and the concentration of each of the complexes formed. Calculated pH values agree with observed values for solutions of known composition.

The computer program described by Wood, Reid & Elvin (1981) has been extended to include the complexes formed in alkaline solutions of Ca citrate and phosphate. Mg complexes are also included. Supersaturation with respect to various solid phases is tested for and the composition of the aqueous phase adjusted accordingly. Additional tests of the program have confirmed its accuracy and shown how the results depend on the values chosen for the relevant equilibrium constants.

The effect of physicochemical characteristics (pH, temperature, composition) of the aqueous phase on the mineral balance in milk and milk retentate has been studied. The ratio of colloidal Ca to total protein decreased with pH, but at any given pH the higher the protein concentration, the higher was the ratio of colloidal Ca to total protein. The solubilization of Ca during cooling and the decrease in soluble Ca during heating were approximately the same in retentates and in milk. Among the components of the aqueous phase, soluble Ca and citrate ions were related to the amount of colloidal Ca.

Additions of potassium iodate to milk at 0·05 and 0·1 mM (10 and 20 ppm) before UHT treatment markedly reduced the rate at which pressure built up during processing. This permitted the use of longer processing times before unacceptable pressures were reached in the heat exchangers. Iodate reduced the amount of protein deposited, particularly in the higher temperature sections of the plant, but had no effect on the deposition of minerals. The more compact nature of the highly mineral deposits offered less resistance to the flow path. Reduction in the amount of protein deposited is likely to be caused by increased denaturation of β-lactoglobulin and oxidation of heat activated sulphydryl groups by the iodate, thus reducing the formation of high molecular weight polymers of sulphur-containing proteins at the heated surfaces. Increasing the level of sulphydryl groups in the milk through the addition of L-cysteine-HCl caused an increase in the amount of deposit formed during UHT treatment. Whilst little detrimental effect on the quality of the milk resulted from additions of iodate at 0·05 mM, milks with 01 mM-iodate became bitter during subsequent aseptic storage. Bitterness was a result of iodate-induced proteolysis of casein.

The addition of potassium iodate to milk at 0·1 mm before UHT treatment resulted in rapid breakdown of αs- and β-casein during subsequent aseptic storage. Maximum rates of proteolysis were observed at storage temperatures of 37–45 °C, but the reaction was strongly inhibited by storage at 55 °C and by increased holding time at 140 °C during the UHT sterilization. Iodate-induced proteolysis of purified αs1-and β-casein was detected only with solutions in the serum phase of raw milk; no proteolysis occurred with solutions in 01·M-phosphate buffer (pH 6·7) or in milk ultrafiltrate, irrespective of whether whey proteins and lactose were also added. Thus, it appears that iodate increased the activity of one or more proteolytic components which were present in milk and were unable to pass through an ultrafiltration membrane. However, it is unlikely that iodate acts by increasing the activity of proteinases produced by contaminant bacteria; the presence of iodate did not affect the activity of a proteolytic enzyme isolated from Pseudomonas fluorescens PM-1. Furthermore, iodate promoted protein breakdown during storage of milk drawn aseptically from the cow and subsequently UHT processed. It is suggested that iodate increased the activity of native milk proteinases, other than plasmin which was inactivated by UHT treatment, possibly by preventing thiol-disulphide exchange reactions during the heating process.

As determined by the standard subjective assay procedure, the minimum in the heat stability–pH curve of milk persisted down to at least 116 °C. However when samples were not agitated during heating the minimum became progressively less pronounced as the assay temperature was lowered and it disappeared at approximately 116 °C. Activation energies (Ea) for unagitated samples were approximately 30 Kcal/mole at pH 6·87 (maximum) and at pH 7·18, throughout the temperature range 116–145 °C and for the pH 6·95 (minimum) sample at 116–125 °C; however Eα for the pH 6.95 sample increased to approximately 100 Kcal/mole in the range 127–135 °C suggesting that some highly temperature-dependent reaction had occurred and caused premature coagulation at certain pH values, i.e. to a heat stability minimum. The stability of concentrated milk (20% total solids) was very low at pH values above 6·9, regardless of whether the samples were agitated or not during heating and the maximum/minimum in the heat stability–pH curve persisted down to at least 90 °C in both agitated and quiescent samples.

Eight samples of milk fat were selected for softening point (SP) range. They were separated into high, medium and low molecular weight triglyceride fractions by silicic acid-column chromatography to enable further separation into triglyceride classes by silver ion adsorption thin-layer chromatography. Correlation between triglyceride class content and SP was low. The molecular species composition of the triglyceride classes was determined and correlated with SP. The best correlations were between SP and some low and some high molecular weight triglycerides of the total fat and the trisaturated (SSS) triglyceride class. Correlation coefficients were determined between SP and mole percentage of individual fatty acids and groups of acids. The highest correlations were between SP and individual short chain-length fatty acids (C4–C10) and groupings of short chain-length acids (C4–C10) and groupings of long chain-length acids (C16–C20). The triglyceride class composition of a sample of milk fat was determined before and after interesterification. Interesterification increased the SP from 31·6 to 36·3 °C and produced increased amounts of both low and high and decreased amounts of medium molecular weight triglyceride molecular species in all triglyceride classes. The increases in the amounts of high molecular weight triglycerides were several times greater than the increase in the amounts of low molecular weight triglycerides.

Soluble extracts of 20 strains of thermophilic lactobacilli (Lactobacillus helveticus, L. lactis and L. bulgaricus) were prepared and added to milk for the culture of 10 strains of Streptococcus thermophilus. Acid production was stimulated in 64·5% of cases for 9 of these 10 strains. The L. helveticus extracts were the most stimulatory, but the same extracts did not always strongly stimulate each strain of Str. thermophilus. The stimulatory effects observed varied with the volume of extract and the strain of Str. thermophilus. The exception was Str. thermophilus 385, which was never stimulated. The stimulatory effects observed were due to aminopeptidases present in the lactobacillus extracts and were not related to a general caseinolytic activity. The possible addition of such extracts to milk for cooked hard cheese is discussed.

Cheese whey was used as substrate for submerged cultivation of 8 strains of 6 species of edible mushrooms (morel mushroom): Morchella crassipes (3 strains), M. angusticeps, M. rotunda, M. deliciosa, M. esculenta and an unidentified Morchella sp. Best growth of morel mushroom mycelium was obtained with one of the M. crassipes strains. The optimum growth conditions for the selected mycelium were as follows: initial pH, ~ 5·0–5·5; temperature, 25–28°C; inoculum size, 150–250 mg mycelium/100 ml whey; N sources: peptone and yeast extract; trace elements: K and Fe. More than 20 g/l mycelium was harvested in the form of pellets. Some growth kinetics studies were also performed. The initial carbohydrate (lactose) content was reduced from 5 to 0·4% at the end of the cultivation period. The specific growth rate of M. crassipes ATCC 13227 was from 1.0 to 6·4 x 10–2, depending on the growth phase. The harvested biomass contained about 45% protein, 5% fat and 8·5% ash (on a dry-weight basis). Essential amino acid content was comparable to the FAO standard, except for methionine, and unsaturated fatty acids predominated in the fat. The results with whey are compared with previously reported data on morel mushroom mycelium growth on waste sulphite liquors.