Analysis of 448 milk samples (11 herds) from caprine udder halves showed that microorganisms were isolated from 21·8% of the samples. California Mastitis Test (GMT) and N-acetyl-β-glucosaminidase (NAGase) were superior to antitrypsin in detecting subclinical infections. Coagulase-negative staphylococci and micrococci were the main species isolated from halves showing no clinical disease. Coagulase-positive staphylococcal infections were associated with a significant increase of all inflammatory parameters. Significantly increased CMT and NAGase occurred when streptococci, other staphylococci or micrococci were present. Infection within one half was reflected as an increase in the inflammatory parameters in the milk of the infected half as well as a slight increase in the inflammation parameters in the adjoining half.

The effect of errors that occur in the diagnosis of intramammary infectious mastitis on the precision of experiments measuring the efficacy of mastitis therapy has been investigated. Diagnostic errors within the range found by experienced workers can create large biases in the apparent cure rate of therapy particularly at cure rates of less than 0·5. Using confirmed methods of diagnosis rather than single samples and reducing the probabilities of false positive and false negative diagnoses to 0·01 and 0·05 respectively, the biases in the apparent cure rates are reduced to acceptable levels. A method is given for calculating the rates of occurrence of false positive and false negative diagnoses from the results of trials using confirmed diagnoses. These errors cannot be calculated from therapy trial data when diagnosis is based on single milk samples.

Because the bias in the measurements of the cure rate is greatest at the lowest levels of elimination, estimates of spontaneous recovery in untreated quarters have the greatest error. For this reason experiments incorporating an untreated control group of infected quarters usually reduce the precision of the therapy trials. An experiment in which the efficacy of a test product is measured relative to a reference product has advantages. It minimizes the difficulties arising from scale of measurement, diagnostic errors and herd differences in response rate, and makes possible comparisons between trials. Further investigations are required on the importance of spontaneous recovery, particularly for studies of Escherichia coli therapy and dry period therapy. The results of this investigation have relevance to all types of mastitis investigation that measure the change in mastitis status of udder quarters, i.e. new infection rates.

Changes in the teat apex before and after different milking treatments were measured with a spring-loaded caliper device known as a cutimeter which could detect changes in thickness of the tissues of the teat end, presumably due to congestion and/or oedema, with a high degree of accuracy (± 2%) and repeatability (r = 0·99). Teat end thickness increased with increasing vacuum level. The mean increase immediately after milking with a conventional cluster was 2% for 24 teats milked at 30 kPa, 8% at 50 kPa and 21% at 70 kPa. At these vacuum levels, the mean increases for the same teats milked with an unconventional (PKME) teatcup were 10, 18 and 25% respectively. Cyclic application of 35 kPa positive pressure to the pulsation chamber of a conventional teatcup operating at 50 kPa reduced teat end thickness by 8% compared with the mean premilking value. Although most teats returned to within ± 2% of their premilking thickness values by 1 h after milking, differences were apparent between different milking systems for up to 4 h postmilking.

The levels of N-acetyl-β-glucosaminidase (NAGase) and acid phosphatase were analysed in tissue from the teat and lactiferous sinus epithelia of dairy cows at different stages of lactation. Enzyme levels were lower in the epithelia of the teat sinus than of the lactiferous sinus. For both enzymes, levels were highest in tissue from post-partum glands, lowest in those from dry and mid-lactation glands. In involuting glands the levels were high, but not as high as the post-partum glands.

The variability of the erythrocyte concentration of the tripeptide glutathione was studied in four flocks of Massese sheep. A relationship was found between glutathione level and stage of lactation in which the second month showed the lowest content. Genotype at transferrin and haemoglobin loci was associated with glutathione levels. Homozygotes at the transferrin locus yielded higher levels, while the D allele at the same locus was associated with lower concentrations. Animals with haemoglobin AA showed higher contents of glutathione. Also, a negative correlation was found between daily milk production and glutathione level.

A reference milk system (Clarke system) using primary reference milks made from preserved natural bovine milks (PNM) and standard reconstituted milk (SRM) has been developed to enable accurate calibration of milk analysing instruments. The PNM have values of 2, 3, 4, 5 and 6% fat and 3·5, 2·7, 3·4, 4·2 and 3·3% protein respectively and can be stored for 4 months without detectable change in fat or protein content. The above reference milk system utilizes SRM as a secondary reference milk to enable regular checking of the stability of the instrument calibration during routine testing (e.g. after every 100 samples). Over several months seven laboratories using 13 fat-testing instruments and seven protein-testing instruments achieved high levels of accuracy in weekly calibrations (coefficient of variation 1·1%) when they used the reference milk system and adhered to the prescribed calibration criteria.

Milk fat was fractionated into liquid (m.p. ⋍ 12 °C), intermediate (m.p. ⋍ 21 °C) and solid (m.p. ⋍ 39 °C) fractions by three different processes—melt crystallization, short-path distillation and supercritical CO2 extraction—and the cholesterol content of these fractions determined. Cholesterol was enriched in the liquid fractions from all three processes, in particular about 80% of the cholesterol being found in the liquid fraction obtained by short-path distillation. The basis of migration of cholesterol into various milk fat fractions was explained by its affinity to various triglycerides (melt crystallization) and by vapour pressure and molecular weight (short-path distillation). It was more complex in the supercritical CO2 extraction process; the interplay of cholesterol affinity toward CO2 and its molar volume, and its vapour pressure enhancement under applied pressure play a role.

Cultures of Pseudomonas spp. strains P10, P12 and P15 grown in whole milk which contained ∼ 1 × 108 viable bacteria ml−1 demonstrated near linear increases in the concentration of short-chain free fatty acids and trichloroacetic acid soluble free amino groups at 20 °C, following either ultra high temperature (UHT) treatment (140 °C for 5 s) or dual heat treatments (140 °C followed by either 57, 60 or 65 °C). The dual heat treatments reduced the rates of lipolysis and proteolysis compared to the UHT treatment by up to 25-fold. The dual heat treatment utilizing 60 °C for 5 min also effectively limited both lipase and proteinase activities in raw milk culture samples which had contained either 6 × 106, 5 × 107 or 1 × 108 viable bacteria ml−1. In this system enzyme activities were reduced by up to 10-fold following dual heat treatment compared to UHT treatment alone.

Soluble proteins and Ca and P salts in the fouling deposit on a mineral microfiltration membrane obtained in static conditions were analysed and compared with those found using dynamic filter conditions in a laboratory pilot installation for milk processing. The serum milk proteins were retained by the porous micellar deposit under both static and dynamic conditions, resulting in progressive fouling of the dynamic micellar membrane, enabling milk to be processed with a mineral microfiltration membrane. Ca and P salts increased fouling probably by allowing better adsorption of casein micelles on the alumina and by acting as intermicellar bonds in the deposit. Fat globules modified porosity, permeability and resistance to matter transfer of the deposit. The dynamic conditions gave a deposit of the same type and structure as with the static conditions although made thinner by the velocity effect.

Samples of caseins having different Ca contents as used in cheese processing were analysed by techniques using differential scanning calorimetry and thermally stimulated currents (TSC) before and after treatment with Na poly-phosphate, a food additive used in the manufacture of processed cheese. These techniques revealed structural changes induced by the salt, and the different types of water molecules associated with the protein are evident. This characterization is in agreement with results obtained by other techniques, particularly X-ray diffraction of proteins. Transmission electron microscopy of the same samples confirmed that the changes observed by TSC were associated with an unravelling of the protein.

To compare the resolving power of starch-urea gel (SUGE) and polyacrylamide-agarose gel electrophoresis (PAAGE) in caprine casein analysis, polyacrylamide gel isoelectric focusing (PAGIF) was used as reference method. The PAAGE or SUGE patterns in the first dimension were allowed to migrate by PAGIF in an orthogonal direction giving rise to two-dimensional (2-D) separations. Using this procedure, some individual bands considered to be homogeneous by SUGE or PAAGE were found to be complex mixtures of casein components. A detailed analysis of the analytical capabilities of SUGE and PAAGE was performed. Procedures based on the densitometric reading of SUGE and PAAGE patterns seemed to give inaccurate results on the quantitative composition of caprine casein. Among the electrophoretic methods assayed, the 2-D procedure gave the best resolution of casein fractions.

The half-life (∼ 2 h) of commercial yeast lactase (Kluyveromyces marxianus) in milk at 45 °C was 20 times greater than in milk salts and 50 times greater than in phosphate buffer. K was a more effective stabilizer than Na, both in milk salts and buffer. Stability was markedly reduced by the absence of divalent cations. Lactose and caseinate both stabilized the enzyme about 5-fold in milk salts, but together they stabilized it almost 50-fold. At equimolar concentrations, galactose was almost as effective as lactose as a stabilizer, but glucose was much less effective and sucrose had no effect. Stability in milk was independent of enzyme concentration, but varied with concentration of milk solids, reaching a maximum at about 25% solids. In milk, enzyme denaturation was more sensitive to changes in temperature in the range 42–53 °C than in the range 30–40 °C. At a concentration of 10 O-nitrophenyl-β-d-galactopyranoside units/ml it took 19 min at 45 °C to achieve 80% hydrolysis of lactose in milk, compared to 87 min at 30 °C.

When the antimutagenic activity of milk or cultured milk components on the pepper-induced mutagenicity to streptomycin-dependent strain SD 510 of Salmonella typhimurium TA 98 was investigated, whole casein showed a significant antimutagenic activity. Heating at 121 °C for 15 min completely destroyed the antimutagenic activity of casein, which was temperature dependent. While acid or papain digestion resulted in the loss of antimutagenic activity of casein, trypsin digestion had little effect although the digestion of casein by each proteinase was over 75%. β-Casein, egg albumin, and bovine serum albumin also had a similar antimutagenic activity to that of whole casein.

Undenatured whey protein (UWP) content of skim milk acidified with lactic acid or cultured with lactic cultures was estimated by a dye-binding method. The UWP content decreased with increase in acidity and the denaturation was only partly reversible on neutralization to the original acidity. The decrease in UWP was higher in cultured milk than in the milk acidified to the same extent with lactic acid, indicating the effect of lactic cultures in denaturation of whey proteins during fermentation of milk. Among the lactic cultures the denaturation effect of Lactobacillus delbrueckii subsp. bulgaricus was highest, followed by Streptococcus salivarius subsp. thermophilus, Lactococcus lactis subsp. lactis and Lact. lactis biovar diacetylactis. Denaturation of whey proteins by lactic cultures was found to be partly irreversible.

The microflora of ten batches of La Serena cheese, made from raw milk of Merino ewes and using vegetable rennet as coagulant, was monitored throughout a 60 d ripening period. After 15 d, lactic acid bacteria predominated in the interior of the cheese, whilst lactic acid bacteria and lactic acid-utilizing species of yeasts and moulds predominated on the cheese surface. Coagulase-positive staphylococci were not detected in the interior or on the surface of any of the cheeses after 45 d and faecal coliforms were not found after 60 d. Higher death rates of staphylococci and coliforms were recorded for cheese made in spring than for the cheese made in winter.

Casein breakdown and free fatty acids formation were studied in ten batches of La Serena cheese throughout a 60 d ripening period. A rapid degradation of αs1-casein occurred, with only 18·6% residual αs1-casein being detected in 60 d-old cheese, whereas 49·5% β-casein remained unattacked. High pH values, low NaCl-in-moisture concentrations and high moisture contents enhanced proteolysis. Lac-tobacilli and yeasts were the only microbial groups which significantly influenced αs1-casein breakdown, and only yeasts affected β-casein hydrolysis. No significant effect of chemical characteristics or microbial groups on FFA levels was detected, an average level of 12·7 mequiv./100 g fat being recorded for 60 d cheese. Rheological characteristics of the cheese reached their minimum values after 15–30 d of ripening and were dependent on αs1- and β-casein breakdown, pH value, NaCl-in-moisture concentration and moisture content.