Non-secretory mammary expiants from virgin goats showed higher RNA and protein synthesis in a low O2 gas phase (air) than in high O2 (95% O2). Lipid and casein synthesis was not affected significantly by the concentration of O2 in the atmosphere during culture. on the other hand, the more developed mammary tissue from primigravid goats showed higher lipid, casein and protein synthesis in 95% O2. The relative response of mammary tissue to hormones was not substantially different when cultured in the presence of a low or high O2 gas phase. As Hepes-buffered medium was found not to need a supply of CO2 to maintain the correct pH and as Hepes did not interfere with biochemical activities of cells, it is recommended to use it for cultures in a low O2 gas phase.

Lactating goats were milked incompletely in one gland and normally in the other gland twice daily for 24 weeks. Yields of the incompletely milked glands were adjusted so that a calculated 100 ml milk remained in the gland at the end of milking. On average this residual volume was greater by 7·6% of the total milk volume than that left after normal milking and was 25·9% greater than the capacity of the alveoli. After 24 weeks, the weekly milk yield of the incompletely milked gland was 23·8% lower than that of the other gland (P < 0·001) when expressed in relation to cell number. The metabolic capacity of secretory cells in the two glands was measured in serial tissue biopsies. Two weeks of incomplete milking had no effect on enzyme activities or metabolic fluxes in the incompletely milked gland, but after 24 weeks the activities of several key enzymes were significantly lower in this gland. This was associated with a reduced rate of synthesis of total protein and casein in expiants freshly prepared from the tissue. The rate of lactose synthesis also tended to be lower in expiants from the incompletely milked gland. Secretory cell number in the two glands was similar at the end of incomplete milking. The data indicate that incomplete milking over a long period caused partial secretory cellular involution via a local chemical feedback mechanism in the gland.

Six lactating, non-pregnant Jersey cows were given subcutaneous injections of recombinantly derived bovine growth hormone for 7 d. Milk yield was increased by 4·5 kg/d on d 7, compared with the average yield of 10·7 ± 0·4 kg/d (mean ± s. e. m.) for the 7d preceding treatment. Concentrations of insulin-like growth factor I (IGF-I) in the milk increased from 0·44 ± 0·04 nmol/1 (mean ± s. e. m.) during the 7 d preceding treatment to 1·6 ± 0·2 nmol/1 on d 7 of treatment. Taking the increase in milk yield into account the total increase in the secretion of IGF-I into milk of one udder half was 6-fold. Plasma concentrations of total IGF-I rose from 15·5 + 1·3 nmol/1 (mean ± s. e. m.) on the day preceding treatment to 56·9 ± 3·6 nmol/1 (mean ± s. e. m.) on d 7 of treatment. Mammary plasma flow increased from 1·6 ± 0·09 to 2·2 ± 0·06 1/min udder half over the same time. Estimates of the amount of IGF-I that reached the mammary gland gave values of 24 and 116 nmol/min udder half before and during treatment respectively. IGF-I in milk of treated cows was associated predominantly with proteins ranging from 40000 to 150000 mol. wt, but a significant proportion (19%) of the total IGF-I was present in the free unbound form. IGF-I crosslinking studies revealed the presence in milk of one specifically labelled band at 31000 mol. wt.

Pituitary-derived bovine growth hormone (bGH) was administered to Jersey cows during late lactation for 7 d. Milk yield increased significantly during treatment and by a maximum of 49·6% on d 7. The magnitude of the increase was similar to that of mammary plasma flow (47·8±18·3%) over the same period. By 15–21 d after treatment, both variables had returned to pretreatment values. With respect to milk composition, bGH had negligible effect on lactose and fat concentrations but there were significant decreases in protein, sodium and chloride. Arterial plasma concentrations of bGH increased substantially during treatment, but the associated rise in insulin was not statistically significant. Haematocrit decreased significantly, the lowest value being recorded 3 d after bGH treatment ceased. Mammary respiratory quotient fell progressively after the start of bGH treatment and reached the lowest recorded value 3 d after treatment ceased (62·2 ± 7·3% of pretreatment value). Glucose and acetate uptake by the mammary gland increased significantly during treatment, increase in glucose uptake being due both to a greater arterio-venous difference and to mammary plasma flow. There was strong evidence that the acute response in increased milk yield was associated with multiple effects in terms of mammary plasma flow and metabolism, as well as haematocrit changes indicative of increased plasma volume.

Concentrations of lactose, α-lactalbumin (α-la), glucose and glucose-6-phosphate were measured in milk obtained from rats under conditions where the rates of milk production varied from 0 to 2·6 g/h. In the milk from rats fed a low protein diet where milk production was 0·9 g/h, the concentration of α-la was 1·5 mg/ml, being significantly lower than that in the milk of control rats at 2·9 mg/ml and where the rate of milk production was 2·6 g/h. No differences were detected in the glucose concentrations. When rats were fed restricted amounts of the control diet and where milk production varied from 0 to 1·7 g/h during the course of the day, no differences in the concentrations of either α-la or glucose were detected. These results suggest that considerable caution must be used in interpreting the significance of milk glucose in the rat.

The term ‘hydraulic milking’ describes a new milking concept in which liner movement is restricted and the liner is flooded with milk beneath the teat. This condition, achieved with a multi-valve claw without air admission to the cluster, reduced milking time by 26% and increased milk flow rate by 20%. Four experiments describe the discovery of hydraulic milking and investigate its potential using equal or different levels of vacuum in the milkline and pulseline. Benefits from hydraulic milking include decreased lipolysis (≤36%) and milk foam (75%), improved teat condition and a high degree of protection against machine-induced infections. Evidence of increased milk yield is inconclusive. Cluster removal is impeded by hydraulic milking and the multi-valve cluster requires modification to facilitate the process. Pulsation characteristics and vacuum levels developed for conventional milking appear adequate for hydraulic milking. Unorthodox vacuum conditions may be needed, however, to exploit fully this novel milking concept.

Results from a field trial involving 23 Norwegian dairy herds support the theory that deflector shields inserted into the teatcup liner can reduce the risk of intramammary infection. However, the effectiveness of this measure is questionable in cows already infected and in problem herds.

Subunit components of ovine, caprine and equine casein micelles were separated by gel chromatography using a TSK-G4000SW high-performance column and the subunit components of the fractions analysed and compared with bovine casein. Molecular weights of the casein complexes were determined by the combined use of high-performance gel chromatography and low-angle laser light scattering. The caprine and ovine caseins were separated into three peaks (F2, F3 and F4) which were similar to those of bovine casein with respect to composition and molecular weight (500, 100 and 23 K). These F2, F3 and F4 peaks consisted mainly of αs- and κ-casein, αs- and β-casein and β-casein respectively. The equine casein was separated into two components corresponding to F3 and F4 of bovine casein. These F3 and F4 peaks consisted mainly of αs- and β-casein and β-casein respectively. The molecular weight of equine F3 (850 K) was different from that of the other three species. The contents of F2 and F4 in these caseins were dependent on the contents of κ-casein and β-casein respectively.

On renneting, the electrical conductivity of milk decreased as viscosity increased. The sigmoidal time course of the decrease resembled the time course of shear modulus, but was more rapid. The total amount of change was independent of the amount of rennet and proportional to milk conductivity and its casein content. The conductivity change was interpreted as a change in the way casein micelles obstructed the path of the charge-carrying ions.

A mathematical model for chymosin action on casein micelles is presented in a two-stage equation which results in a single curve demonstrating the lag time from enzyme addition to the end of coagulum firming. The model uses the Michaelis–Menten enzyme kinetics equation for the first reaction followed by an nth order reaction for the casein micelles agglomeration stage. The computer output using these equations shows that lag time is elongated as enzyme concentration is lowered. Regression analysis of time of gelation against l/E0 shows good correlation. Viscosity of the milk drops at the beginning of the κ-casein hydrolysis and increases thereafter, when the coagulum is being formed.

Effects of the reaction variables pH, temperature, time, enzyme concentration and solids concentration on the hydrolysis and solubilization of lactalbumin slurries by Alcalase have been determined. Reaction progress curves, solubilization v. time, were very unusual with a maximum solubilization of 96% occurring at a short reaction time corresponding to a degree of hydrolysis of 11–12%. Further hydrolysis beyond this point produced a rapid decrease in solubilization to about 67%, followed by a further gradual increase in solubilization with prolonged hydrolysis. The unusual solubilization profile was also produced by increasing enzyme concentration at fixed reaction time. The effects of pH, temperature and solids concentration were similar to those found in the hydrolysis and solubilization of other insoluble proteins. The implications of the results for the design and operation of an enzymic hydrolysis process are discussed.

Dietary manipulation was used to produce a similar series of milks from both Friesian and Jersey cows. The gross compositions of the milks, the fatty acid (FA) composition of the milk fats, the distribution of molecular sizes in the triglycerides of the milk fat, the melting properties of the milk fats, and the whipping properties of creams containing 360 and 400 g fat/kg were measured. Changes in gross composition and FA composition were as expected from the use of dietary oil supplements, but it was established that the mathematical relation between 18:0 and 18:1 differed between breeds, the Jersey yielding a milk fat with a lower proportion of 18:1 for a given value of 18:0. Control diets free from added fat produced milk fats with essentially unimodal triglyceride distributions, whereas fatrich diets produced bimodal distributions. The slight differences in these distributions between breeds were merely a reflection of variations in FA composition rather than in synthetic procedures. Differences in the whipping properties of creams containing 360 and 400 g fat/kg were consistent with literature observations. Dietary manipulation had little effect on the whipping properties of creams derived from Friesian cows, but caused considerable changes in the corresponding properties of the creams from Jersey cows. The only property that behaved similarly in the creams from the two breeds was the butter time, i.e. the time taken for butter granules to form on prolonged whipping of the cream. A major determinant of the butter time appeared to be the proportion of the fat that was molten at the temperature at which the whipping experiments were carried out.

Glutamic acid uptake in Streptococcus salivarius subsp. thermophilus was energy dependent, the source of energy and adaptation to sugar being important to efficiency of uptake. The disaccharides, lactose and sucrose, stimulated uptake, but cells grown in glucose were more active. Optimum temperature was ˜ 40 °C and pH ˜ 7·0. NaCl was strongly inhibitory to the uptake of glutamic acid although not to that of isoleucine. High specificity existed because only L-aspartic acid was inhibitory.

β-Galactosidase from an autolytic strain of Streptococcus salivarius subsp. thermophilus was purified 109-fold to near homogeneity. The yield of purified enzyme was 41% and the specific activity was 592 0-nitrophenyl β-D-galactopyranoside U/mg at 37 °C. Two isozymes were present, but only one subunit was detected, having a mol. wt of 116000. Enzyme stability was 37–83 times greater in milk than in buffer in the range 60–65 °C. At 60 °C the half-life in milk was 146 min. Denaturation in buffer was first-order, but in milk the overall reaction order with respect to enzyme concentration was ˜ 0·5. The activation energy for denaturation was 453 kJ/mol in milk and 372 kJ/mol in buffer. In milk the activation energy for lactose hydrolysis was 35·1 kJ/mol.

Two l·9 1 Upflow Anaerobic Sludge Blanket (USAB) reactors, operated at 35 °C, were used for the digestion of deproteinated cheese whey substrate. The C/N ratio was 19, and the alkalinity requirements of the two reactors were satisfied by adding Ca(OH)2 and Na2CO3 in two different ratios respectively. Gas and effluent parameters indicated that reactor 1 (receiving a higher level of calcium) was superior and eventually a loading rate of 7·1 kg COD m−3 d−1 could be obtained in this reactor, compared to a loading rate of 5 kg COD m−3 d−1 which was obtained in reactor 2. Pellets with good settling abilities formed in reactor 1, while the sludge in reactor 2 developed a granular slimy appearance and settled poorly. Investigation of the ultrastructure of the sludge particles revealed a difference in the types of bacteria present in the granules.

The extent and level of proteolysis were evaluated in Cabrales and five other European blue vein cheese varieties, Bleu de Bresse, Danablu, Edelpilzkäse, Gorgonzola and Roquefort, by analysing their different N-containing constituents and determining the degree of casein hydrolysis. The electrophoretic patterns of the caseins in the cheeses confirmed their strong proteolysis, components featuring the lowest electrophoretic mobility offering the greatest resistance to subsequent hydrolysis. Component αs1 — I was detected in all varieties studied with the exception of Roquefort cheese.

The manufacture of Domiati cheese by ultrafiltration (UF) processing of recombined milk bas been described in several reports (El-Shibiny et al. 1982; Bogaard, 1986). This method has several potential advantages in areas short in milk production. In Egypt, a new plant has been established recently for the manufacture of Domiati cheese on the basis of this technology.

The behaviour of fresh pasteurized skim milk during UF has been described (Glover, 1971; Setti & Peri, 1976; Patel & Reuter, 1985; Chiang & Cheryan, 1986). Similar studies are lacking for reconstituted skim milk or recombined milk. Skim milk powder is usually subjected to variable heat treatments during processing which are known to affect its properties. These heat treatments have been used as a basis for classification of skim milk powders. Therefore, studies on UF of reconstituted milks previously subjected to different heat treatments would be important in the adaptation of this technology to cheese manufacture.

We describe here results obtained for permeation rates of reconstituted skim milk during UF compared with fresh pasteurized skim milk.

It is of industrial importance to investigate the interaction of Streptococcus lactis with phages. Although it has been long recognized that in phage–bacterial relationships the phage-carrier state can occur (Hunter, 1947), relatively little study has been done on this subject. The terras ‘phage-carrier state’ and ‘pseudolysogeny’ have been used synonymously to describe bacterial cultures which are persistently infected with a virus (Barksdale & Arden, 1974, Lawrence et al. 1976). The phagecarrier state differs from lysogenesis in that the bacteria are easily separated from the bacteriophage by a simple plating and re-isolation procedure (Graham et al. 1952). Süssmuth & Tayran (1986) showed that after lysis of one single strain, phage and phage-insensitive bacteria coexist. This work investigates the proportion of phage-insensitive bacteria remaining after lysis of other Str. lactis strains, the effect of calcium on this proportion, and the number of generations required to return to a normal sensitive population.

The major problem encountered in the dairy industry is due to the failure of starter in the manufacture of fermented dairy products such as cheese, Yogurt buttermilk and also the Indian fermented milk products srikhand and dahi, in terms of low acid production and absence of flavour and aroma. Usually, in such cases the presence of antibiotics is detected. Little work has been done on the effect of antibiotic resistance in the starter on flavour production, though many workers have investigated acid production and proteolytic activity (Kondratenko et al. 1978 Ottogalli et al. 1975; Shahani & Harper 1958; Wilkowske & Krienke, 1951). The present investigation has been undertaken to develop antibiotic-resistant strains of lactic streptococci, i.e. Streptococcus lactis biovar. diacetylactis and Lactobacillus delbrueckii subsp. bulgaricus which could be used for the preparation of fermanted milk products.