A comparison of three different media, yeast dextrose agar, tomato dextrose agar and acetate agar (which is selective for lactobacilli) showed that the acetate medium was satisfactory for the isolation and counting of lactobacilli from Cheddar cheese during ripening. Lactobacilli were isolated on this medium in the early stages of ripening when the large numbers of starter streptococci growing on the other media were completely suppressed. Lactobacilli isolated were identified biochemically and serologically. Serological typing was found to be a useful method of identifying large numbers of isolates and of assessing the incidence and distribution of particular types in the cheese.

We wish to thank Dr A. T. R. Mattick for his interest and helpful advice in this work; Dr L. A. Mabbitt for preparation of the cheese samples; Miss H. R. Chapman for making the experimental cheese; and Mrs P. Jarrett for technical assistance.

This study investigates the potential of Fourier transform infrared spectroscopy (FTIR) to monitor glycation-induced changes in protein structure. Aqueous solutions of sodium caseinate and glucose (1:2 w/w, pH 6·7) were heated at 90°C for 0, 10, 20, 40 and 60 min. Evidence for caseinate glycation was obtained by mass spectrometry techniques (electrospray (ESI) and matrix-assisted laser desorption ionisation (MALDI)). FTIR was able to discriminate between glycated and non-glycated sodium caseinate, when the data were analysed by multivariate statistical methods; principal component analysis (PCA) and soft independent modelling of class analogy (SIMCA). The techniques used were complementary and provided different levels of information about the glycated samples.

The influence of pH, temperature and Ca depletion on bovine casein micelle suspensions in D2O containing simulated milk ultrafiltrate was studied by 1H-NMR spectroscopy.

In the pH range of 5·8–7·5 the spectrum of the micelles showed very little pH dependence, indicating that no changes occurred in the dynamic behaviour of the proteins constituting the micelle.

The NMR spectrum of casein micelles was strongly temperature dependent, particularly in the temperature range of 60–98 °C. Increase in temperature resulted in a strong increase in spectral intensity concomitant with changes in the spectral characteristics. In micelle suspensions these changes were reversible, and indicated that at clevated temperatures the rigid structure of the casein micelle started to melt, leading to an increased mobility of appreciable parts of the proteins in the micelle.

Ca depletion of the casein micelles by addition of EDTA resulted in an increase in spectral intensity, which arose from the presence of casein components in the serum phase, The spectrum of these serum phase particlcs resembled closely the spectrum of a solution of total casein in simulated milk ultrafiltrate and was quite different from the spectrum of casein micelles.

The implications of these results with respect to models of the structure of bovine casein micelles are discussed.

A survey was carried out in 2003 in 49 dairy herds to determine the overall and pathogen-specific prevalence of intramammary infection (IMI) in Dutch dairy herds, and to compare the distribution with four studies performed from 1973 to 1985 in The Netherlands. Herds were randomly selected stratified over the 12 Dutch provinces, had at least 40 lactating cows and participated in the Dutch milk recording system. Quarter milk samples were collected from all 408 cows with a somatic cell count (SCC) ⩾250 000 cells/ml and 145 heifers with SCC ⩾150 000 cells/ml at the last milk test before the farm visit. Additionally, samples were collected from 519 (approximately 25%) of the remaining low-SCC cows and heifers with a SCC at the last milk test before the farm visit of <250 000 and <150 000 cells/ml, respectively. Bacterial growth occurred in 37·3% of milk samples of high-SCC cows and in 21·1% of low-SCC cows. Coagulase-negative staphylococci (CNS) were the most frequently isolated group of bacteria (10·8% of quarters) and were found in all herds. Prevalence of Staphylococcus aureus IMI was lower in 2003 than in 1973, respectively 1·8% and 6·2% of quarters. Prevalence of Streptococcus uberis and Str. dysgalactiae IMI was almost the same in the five samplings during the 30-year period, at 1·1–1·7 and 0·9–1·5%, respectively. Str. agalactiae was not found in this study. Prevalence of CNS IMI was higher in lactating heifers, while prevalence of Str. uberis, Str. dysgalactiae and penicillin-resistant Staph. aureus IMI was higher in older cows. Because distribution of pathogens changes over time, herd-level samples for bacteriological culturing must be taken regularly to monitor udder health. Additionally, national mastitis prevalence studies give important information through monitoring the national udder health status.

Two feeding systems trials were carried out to determine the antioxidant activity of soft goats' milk cheeses, and also to evaluate the presence of bioactive polyphenolic compounds. Two groups (A and B), each one with 20 (BW 50±5 kg) French Alpine goats were employed. All animals had between 70 to 80 milking days and were milked once a day. Group A included daily grazing on shruby rangeland vegetation, and group B was kept in full indoor confinement. Thirty kg of goats' milk from each group were collected; 15 kg from each were pasteurized and the remaining 15 kg were not pasteurized (raw), resulting in four treatments (two feeding system×two milk treatments). Soft goat's cheese antioxidant activity can be modified by the animals feeding system; grazing management represents a better option than indoor feeding to produce a healthy profile of bioactive compounds; providing an increase of total polyphenol, hydroxycinnamic acids and flavonoid concentrations. Pasteurization did have a significant effect on these metabolites, and diminished total polyphenol concentration. More research is needed to elucidate the potential of soft goat's cheese as a functional food.

Teat and gland cistern of the mammary glands of five dairy cows, five goats and five sheep were scanned in a water bath during α- and β-adrenergic agonist and oxytocin administration. A 5 MHz linear array scanner was used to create vertical cut pictures with the scan plane longitudinally through the teat channel. The i.v. injection of the α-adrenergic agonist phenylephrine (30 μg/kg) induced diminution of the section area through teat and gland cistern by 38±17% on average within 1 min in all three species. In contrast, the i.v. injection of the β-adrenergic agonist isoproterenol (1 μg/kg) did not change the cisternal areas. The i.v. injection of oxytocin (2·0 × 10−3 i.u./kg) elicited an enlargement of teat and gland cistern area by 48±12% on average. Ultrasonography proved to be a valuable system for visualizing changes of the cisternal volume. Smooth muscle contractions in response to phenylephrine administration are thought to cause area reduction, whereas an expected smooth muscle relaxation after injection of isoproterenol could not be observed by ultrasonography. Milk ejection as induced by oxytocin administration caused dramatic enlargement of the cistern area in all three species.

Three cationic materials markedly reduced the rennet clotting time of casein micelle suspensions, the efficacy of each being primarily dependent on the charge and the amount absorbed by the micelles. The reduction in coagulation time was unaffected by components of the milk serum other than salts. No enzymic action by lysozyme on casein micelles was detected. All materials acted by the same mechanism, increasing the affinity of rennet for the micelles and accelerating the aggregation phase. Coagulation did not occur until a minimum amount of κ-casein had been hydrolysed to para-κ-casein. All additives increased the proportion of added rennet retained by the casein in the coagulum. The results indicated that coagulation occurs by specific interactions between micelles modified by rennet.

The combination of ultrasound and heat (thermoultrasound) is an emerging food preservation technique that retains higher quantities of bioactive components compared with current thermal pasteurization practice, but has not yet been assessed for pasteurizing human milk. Artificially contaminated human milk samples were treated with ultrasound (20 kHz, 150 watts) with and without heating. The retention of four human milk proteins was quantified by biochemical assay and laser scattering particle sizing was used to determine the extent of homogenization. While ultrasonic treatment was effective at inactivating Escherichia coli (D4 °C=5·94 min), Staphylococcus epidermidis exhibited resistance (D4 °C=16·01 min). Thermoultrasonic treatment was considerably more effective (Esch. coli D45 °C=1·74 min, D50 °C=0·89 min; Staph. epidermidis D45 °C=2·08 min, D50 °C=0·94 minutes) with a predicted retention (2·8 min treatment, 50°C) of secretory IgA lysozyme, lactoferrin and bile salt stimulated lipase of 91, 80, 77, and 45%, respectively. Homogenization of the milk samples occurred after 5 min and 2 min of ultrasonic and thermoultrasonic treatment, respectively. Thermoultrasonic treatment is an effective method for pasteurizing donor human milk and retaining a greater proportion of bioactive components compared with current practices. However, further studies are required to assess the practicality of applying this technique routinely to donor human milk.

The effects of 2, 4, 7 and 10% supplements of tallow to a basal diet low in fat on the composition of volatile fatty acids (VFA) in the rumen and on the secretion in milk of fat and its component fatty acids are reported. There were no significant effects of the tallow on rumen VFA or on the secretion of total milk fat. The yields in milk of stearic (18:0) and oleic (18:1) acids were positively correlated and those of palmitic (16:0) and myristic (14:0) acids negatively correlated with their respective dietary intakes. Apart from butyric acid which increased, the yields of other short-chain acids synthesized within the mammary gland decreased with increased intake of tallow. Possible factors influencing the output of total milk fat through a balance between increased transfer to milk of dietary fatty acids and decreased intramammary synthesis of fatty acids are discussed.

One hundred and thirty-seven (Holstein (41), Montbéliarde (42) and Tarentaise (54)) dairy cows in first or second lactation received during winter one of two levels (high, H; low, L) of energy intake, and were later fed identically at pasture. Thrice in winter and twice at pasture, the chemical composition and coagulation properties of individual milks were measured. Milk from Holstein cows had lower casein and calcium contents, and poorer coagulation properties (curd firming time and curd firmness) than that from Montbéliardes and Tarentaises (P < 0·01). These differences practically disappeared when taking into account the distribution of the different κ-casein variants and milk casein content. κ-BB milks had coagulation properties 20–50% superior, according to characteristic, to those of AA milks. In the three breeds, animals from the H group had casein contents higher by 1·4 g/l than those of the L group, which induced a significant improvement in curd firming time, curd firmness and cheese yield. Turning out to pasture induced an increase of 0·02 in milk pH, and improved milk coagulation properties. These changes did not appear to result entirely from the parallel increase in milk casein content.

A method of extracting cheese juice is described. Juice from a single one-month-old Cheddar cheese was used to investigate the relationship between the composition of the cheese juice and the occurrence of crystalline aggregates in the cheese. Two classes of crystalline aggregates were identified by light microscopy and also by electron microscopy in combination with X-ray microanalysis: the larger class contained both Ca and P whereas the smaller class contained Ca but not P. Concentrations of ions in the cheese and cheese juice were determined and corrected for the excluded volume of co-solutes and other phases present. When this was done, comparison of the concentrations of Na, K, Cl and lactate in the cheese and the cheese juice indicated that they were virtually entirely in solution, whereas appreciable amounts of the total Ca, P and P1 in the cheese were not extracted in the cheese juice. The amounts of the non-extractable salts were consistent with the volume fractions of the crystalline aggregates found by microscopy; calculations of the ion equilibria in the cheese juice showed that it was supersaturated with respect to various Ca phosphate salts and to tricalcium citrate. It is concluded that the physicochemical origin of the crystalline aggregates was the nucleation and growth of crystals from a supersaturated solution, though the sites of nucleation may have been formed by the microbial activity in the cheese. Of the free amino acids found in the juice, none was at a sufficiently high concentration to form a saturated solution, indicating that in this relatively young cheese the crystalline aggregates were not formed from amino acids.

Molecular biology techniques have been used for species identification in food of animal origin in relatively recent years. A polymerase chain reaction (PCR) based method, the multiplex PCR, was recently applied to species identification in meat and meat products. It allows co-amplification of separate regions of a single gene or specific fragments, each typical of a different animal species in a single PCR reaction, using different pairs of primers in the same reaction mix. In the present paper, the duplex-PCR technique is proposed to identify bovine and water buffalo DNA in a single PCR assay in milk and mozzarella cheese (a typical Italian cheese, originally made from pure water buffalo milk). Because of its lower cost, undeclared bovine milk is added to water buffalo milk for making different kinds of mozzarella cheese. The results of this experiment indicate the applicability of this method, which showed an absolute specificity for the two species and a high sensitivity even down to low DNA concentrations (1 pg). In bovine and water buffalo mixtures of both milk and mozzarella cheese, the minimum concentration tested was 1% of bovine in water buffalo milk and water buffalo in bovine milk. The importance of the somatic cell content in raw milk is also discussed with special reference to the evaluation of mixtures (milk or cheese) of the two species.

Short-term associations between disease and milk yield were studied in 1594 lactations occurring between 1977 and 1982 in 732 Friesian, Ayrshire and Holstein crossbred cows. Statistically significant differences in milk yield between one week before and one week after clinical diagnosis were observed for ketosis (5·l kg/d), hypomagnesaemia (4·1 kg/d), mastitis occurring after peak yield (2·1 kg/d) and lameness (1·1 kg/d). Milk yield declined for as much as 2–4 weeks before diagnosis of disease, and total losses in milk yield associated with ketosis or hypomagnesaemia were estimated to be 60–70 kg. No significant differences were found for endometritis or for mastitis when it occurred before peak yield. Milk yield was suppressed for about 4 weeks after calvings with retained placenta, but there were no corresponding effects of dystocia or hypocalcaemia on milk yield. It is suggested that if automatic daily milk recording is available it may be possible to detect deviations from normal, and hence detect subclinical disease 2 or more weeks before its clinical appearance.

Analytical electrophoresis of native and of rennet-treated casein micelles was carried out at 26 and at 5°C in a sucrose density gradient in a medium of the same ionic composition as milk. Under normal circumstances, the micelles were negatively charged and showed little heterogeneity in the electric field, the fastestmoving ones having at 26°C a mobility not more than 30% greater than that of the slowest. Native micelles were more highly charged at 5 than at 26°C; at each temperature, the mobility was approximately halved by rennet treatment. The results suggest that the effects of rennet treatment and of alterations in temperature on the tendency of the micelles to clot can be entirely explained as being caused by changes in charge.

Comparisons are made between the sulphur-containing volatiles of 4 Cheddar cheeses, using a gas chromatograph equipped with a flame photometric detector.

Two of the cheeses were made aseptically from whole milk, with and without starter, the third was made from whole milk with starter in an open vat, and the fourth was made from skim-milk also in an open vat. Only the cheeses made from whole milk with a starter culture developed normal Cheddar flavour; the cheese made without starter and the skim-milk cheese had little or no flavour.

Considerable differences were found in the chromatograms of the 4 distillates and in particular methanethiol was found only in the distillates from the cheeses having Cheddar flavour.

Considering that several health promoting properties are associated with kefir consumption and a reliable probiotic product requires a complete identification of the bacterial species, the present work evaluates several proved markers of probiotic potential of eleven isolates of homofermentative lactobacilli isolated from kefir grains and molecular identification and genotypic diversity. Using restriction analysis of amplified ribosomal DNA (ARDRA) and analysis of the 16S–23S rRNA internal spacer region we confirmed that all homofermentative lactobacilli belong to the species Lactobacillus plantarum. RAPD-PCR analysis allowed the discrimination of lactobacilli in five clusters. All isolates exhibited high resistance to bile salt. High survival after one hour of exposure to pH 2·5 was observed in Lb. plantarum CIDCA 8313, 83210, 8327 and 8338. All isolates were hydrophilic and non autoaggregative. Isolate CIDCA 8337 showed the highest percentage of adhesion among strains. All tested lactobacilli had strong inhibitory power against Salmonella typhimurium and Escherichia coli. Seven out of eleven isolates showed inhibition against Sal. enterica and five isolates were effective against Sal. gallinarum. Only CIDCA 8323 and CIDCA 8327 were able to inhibit Sal. sonnei. We did not find any correlation between the five clusters based on RAPD-PCR and the probiotic properties, suggesting that these isolates have unique characteristics.

The objective of the present work was to identify the compositional parameters of raw milk that affected ethanol stability at natural pH when natural milk conditions were not modified. Heat stability, measured as coagulation time (CT), was included in the analysis to verify relation to alcohol test. Statistical models were proposed for alcohol and heat (CT) stabilities. Milk samples of good hygienic quality from dairy farms were classified in two groups according to their alcohol stability. Unstable samples to ethanol (72%, v/v) presented lower values of pH, somatic cells count, casein and non-fat-solids relative to ethanol stable samples (ethanol at 78%, v/v or more); whereas freezing point, chloride, sodium and potassium concentrations were higher in the unstable group. Logistic regression and multiple regression were applied to modelling alcohol and heat stability behaviour respectively. Chloride, potassium, ionic calcium and somatic cell count were included in the alcohol regression model, whereas calcium, phosphorous, urea, pH and ionic calcium were part of CT model. Ionic calcium was the only measured variable that contributed to both models; however coagulation time was noted to be more sensitive to ionic calcium than alcohol. The relation between ionic strength and casein was found to contribute to the alcohol model but not to the CT model. However, the interaction calcium plus magnesium plus phosphorous and casein contributed only to CT model.