The composition and weight of deposit formed in all sections of an ultra-high-temperature milk sterilization plant were determined. Deposits formed in the preheating, heating and cooling sections during sterilization of pasteurized whole milk were analysed for dry matter, protein, fat and mineral contents. The weight and composition of components of the deposit varied in different sections of the plant and with the heating temperature. Two categories of deposit could be distinguished: one in the preheating section consisting of (w/w) protein 50%, minerals 40% and fat 1% and another in the heating section consisting of minerals 75%, proteins 15% and fat 3%. Concerning the rate of formation of these deposits, a comparison of the results with those obtained for pasteurization shows that fouling was more rapid during pasteurization of raw milk than during sterilization of previously pasteurized milk. Hypotheses concerning mechanisms of formation of protein deposition are discussed.

Seven variables – electrical conductivity (EC), somatic cell count (SCC), N-acetyl-β-D-glucosaminidase (NAGase), lactose, protein, fat and pH – were compared in four quarter milk fractions (MF1: strict foremilk; MF2: first 12–15 ml foremilk; MF3: subsequent 40–45 ml milk; MF4: strippings) and in one cow composite milk sample (CC) per cow. The study used 142 quarters from 37 lactating cows of the German Black Pied breed. To rule out any possible effect due to management, animal physiology and analytical procedures, the collection and processing of milk samples from each cow was repeated for three consecutive days, and the means of 3-d values were used. All variables were affected significantly by milk fraction and udder health. Compared with foremilk, EC, lactose and protein levels in strippings decreased, while SCC, NAGase and fat increased. The pH of foremilk and strippings did not differ significantly in healthy or in mastitic quarters. The difference between MF1 and MF2 was significant for EC in mastitic quarters, and for SCC in healthy quarters only. In general, mastitis resulted in a significant increase in EC, SCC, NAGase and protein but in a decrease in lactose and fat contents of milk in one or more of the milk fractions studied. Comparison of cow composite milk samples from healthy and mastitic cows revealed the significance (P<0·01) of udder health for EC, SCC and lactose. Of the different parameters that can distinguish between healthy and mastitic quarters or cows, EC could be used to classify 76% of quarters and 73% of cows correctly, while the lactose content permitted correct identification of 81% of quarters and 76% of cows. NAGase and pH could be used to determine the status of 73% and 61% of quarters, respectively. In general, the correlation observed in strippings was higher than in foremilk for almost all the variables studied. Surprisingly, EC, SCC, NAGase and lactose in milk from healthy quarters of mastitic cows (with at least one mastitic quarter) differed significantly (P<0·05) from those from healthy quarters of cows with all four healthy quarters, indicating an inconsistent effect of mastitic quarters on neighbouring healthy quarters (quarter interdependence).

The thermal behaviour of β-lactoglobulin was studied by differential scanning calorimetry (DSC) in the temperature range 40–160 °C. The DSC curves revealed, in addition to the usually observed denaturation peak near 80 °C, a distinct endothermal peak between 130 and 150 °C. When the pH was increased from 6·5, the area under the peak near 80 °C (denaturation heat) decreased significantly, whereas the peak area near 140 °C increased. The temperature of maximum heat absorption in the peaks near both 80 and 140 °C gradually increased as the pH decreased. Addition of sugars and variation of the heating rate both caused a temperature shift of the endothermal heat effect at 140 °C, similar to that at 80 °C. No peak near 140 °C was observed when β-mercapto-ethanol was added to the β-lactoglobulin solution before scanning. The origin and nature of the high temperature denaturation peak is discussed in terms of conformational changes of the protein.

A comparative study was carried out on the flavour constituents of bovine, ovine, caprine and water buffalo fresh raw milks. The volatiles were isolated from milks by means of vacuum distillation and liquid–liquid extraction. Eighty neutral volatile compounds were identified using high resolution gas chromatography (HRGC) and HRGC-mass spectrometry. About 30 of these components have not been detected previously in milk. The volatiles in milk were similar for the four species, although several quantitative differences might explain the different odours. The volatiles consisted mainly of ethyl esters, especially those derived from butyric and hexanoic acids. Dimethylsulphone alone comprised ~ 25% of the volatile components in bovine, caprine and ovine milk, but only 4% in buffalo milk. Among the aldehydes, pentanal and nonanal were the most representative. Other aldehydes were present selectively: 3-methylbutanal was found only in buffalo milk; phenylacetaldehyde and benzaldehyde were present in large quantities in caprine milk, and in trace amounts in the other milks. The content of ketones, mainly 2-methylketones, was higher in buffalo milk than in the other three types. Alcohols varied between species, from 1·5% (bovine) to 5% (buffalo). Among these, 1-octen-3-ol and phenylethanol could be particularly important for the aroma of milk. The level of l-octen-3-ol in the milks was: buffalo > ewe > goat ≫ cow. Phenylethanol was not found in ewes' and goats' milk and its concentration in buffalo milk was 100 times higher than in bovine milk. Finally, indole and 4-methylphenol, interesting because of their odorant properties, were present in higher quantities in buffalo, ewes' and goats' milks than in cows' milk.

The highest incidence of lipolytic activity among the psychrotrophic Gram-negative flora of commercial raw milks was found in strains of Pseudomonas fluorescens and Ps. fragi. The lipases of all of the lipolytic strains remained wholly or partly active after heat treatment at 63°C for 30 min. Two of the strains tested further had lipases which retained 20–25% of their activity even when heated at 100 °C for 10 min. Cheeses made from milks in which strains or a single strain of lipolytic Gram-negative rods (GNR) had been allowed to multiply to > 107 colony forming units/ml became rancid after 4 months even though the GNR had been killed by pasteurization. The rancidity was characterized by a soapy off-flavour in cheeses containing free fatty acid concentrations from 3 to 10 times higher than those in control cheeses made from stored milks with low counts of GNR. Strong rancidity could be reproduced by adding the culture supernatant of a pre-grown lipolytic strain, but not the washed cells, to milk and pasteurizing it immediately before cheese-making, demonstrating the extracellular nature of the rancidity-inducing lipases.

Small numbers of Escherichia coli were infused into both lactating and non-lactating udders. Twelve of the 17 lactating quarters infused became infected, and all 12 showed clinical symptoms of udder disease. The 5 lactating quarters which did not become infected all had pre-infusion somatic cell counts > 300000 cells/ml milk, whilst all the quarters which became infected had cell counts < 300000 cells/ml milk. E. coli was subsequently recovered from only 6 of the 16 non-lactating quarters infused. In only 2 of these quarters did clinical infection follow, both quarters being in a cow infused 2 d before calving. The remaining 4 quarters from which E. coli was recovered were all negative within 5 d of infusion. These differences in susceptibility are discussed, particularly with reference to the frequent occurrence of coliform mastitis at and shortly after calving.

Destabilization of emulsion droplets is described in terms of flocculation, coalescence and adsorption processes, and then discussed with reference to various technological aspects of dairy emulsions. A semi-quantitative measurement of homogenization-induced flocculation of cream is described using measurements on the time-dependent decrease in viscosity that occurs during shear. The whipping of cream is discussed in terms of the adsorption of fat droplets to air bubbles and the formation of a fat particle network with the fat directly in contact with air. The whipping of homogenized creams is shown to be dependent upon the structure of the newly formed milk fat globule membrane. Since the major protein component of the membrane is casein, any change in casein micelle stability is reflected in the whipping properties of the cream.

The presence of crystalline fat within emulsion droplets is essential for many destabilization processes. Fat crystals pierce the film between 2 approaching interfaces, thus leading to aggregation. The contact angle between fat crystal, oil and aqueous phase can be used to describe the susceptibility of an emulsion to destabilize.

A quantitative measure of emulsion destabilization under shear is described kinetically in terms of reversible flocculation followed by coalescence. The measurement of emulsion viscosity as a function of time at constant shear stress is used to monitor the aggregation processes and the 3 rate constants evaluated by computer curve fitting.

Heat stability profiles of a number of indigenous bovine milk enzymes were examined with the object of being able to monitor heat treatments slightly more severe than typical pasteurization conditions by measurements of residual enzyme activity after heating. Assay procedures were limited to simple fluorimetric, or preferably colorimetric, methods that would be most likely to form the basis of a quick, simple and inexpensive test. Both lipoprotein lipase and α-fucosidase were relatively sensitive to heat and were totally inactivated at temperature/time combinations below those of pasteurization, but the latter may be satisfactory for studying temperatures in the range 55–65°C. Rather more heat stable were N-acetyl-β-glucosaminidase and γ-glutamyl transpeptidase, which may be most appropriate for 65–75°C and 70–80°C respectively. Higher temperature treatments between 80 and 90°C could best be investigated by following α-mannosidase or xanthine oxidase activity.

Opioid antagonists were sought in the fragments of κ-casein which were obtained by chemical synthesis and enzymic digestion. A synthetic bovine κ-casein peptide (35–41), Tyr-Pro-Ser-Tyr-Gly-Leu-Asn (casoxin A) showed opioid antagonist activity at 200 μM in the guinea pig ileum assay. A synthetic peptide Tyr-Pro-Tyr-Tyr (casoxin B) which is found in bovine and human κ-casein, also showed opioid antagonist activity at 100 μM. Another opioid antagonist peptide (casoxin C) was isolated from tryptic digests of bovine κ-casein by reverse-phase HPLC. The structure of the peptide was Tyr-Ile-Pro-Ile-Gln-Tyr-Val-Leu-Ser-Arg, which corresponded to κ-casein (25–34). Casoxin C was active at 5 μM in the guinea pig ileum assay. Thus, bovine κ-casein contains three potential opioid antagonist sequences.

In situ light scattering, where light scattered from a sample is measured directly while the sample is heated in the instrument, is presented as a simple and effective technique for studying the heat-induced aggregation of β-lactoglobulin. This technique was shown to be applicable not only to monitoring the initial aggregation steps, but to following the overall aggregation process with time. The experiments gave results similar to measurements carried out after a heat-quench treatment, but were more informative. From experiments on a standard NIZO β-lactoglobulin sample, a strongly desalted standard NIZO sample, different genetic variants of β-lactoglobulin and a mixture of these, we concluded that the standard NIZO sample was suitable for studying heat-induced aggregation. This sample has been investigated more extensively. Results with β-lactoglobulin (10–100 g/1) at 65 °C fitted a kinetic model for the denaturation and aggregation of β-lactoglobulin. This model, which held for β-lactoglobulin dissolved in water at near neutral pH and at 60–75 °C, recognizes an initiation, propagation and termination reaction, by analogy with polymer radical chemistry. It gave a quantitatively correct description of the dependence of the scattering intensity on the initial β-lactoglobulin concentration. Salt composition, pH and temperature strongly influenced the aggregation of β-lactoglobulin. Particle size increased with salt concentration in the range studied (up to 20 mM-NaCl and 1·0 mM-CaCl2). When the pH increased from 6°9 to 8·0 particle size was strongly reduced, whereas it strongly increased when pH was lowered to 6·2. Between 61·5 and 70 °C temperature did not affect particle size, whereas aggregation rate strongly increased. These effects could be incorporated in the kinetic model via the reaction constants of the reaction kinetic pathway.

Thirty-two lactating Karagouniko ewes were allocated at random to four groups for 6 weeks, to examine the effect of four diets: C (control treatment, ration without algae); LA (ration with low level of algae); MA (ration with medium level of algae) and HA (ration with high level of algae); containing 0, 23·5, 47 and 94 g algae, respectively, on the enrichment of milk and dairy products. Addition of algae reduced (P<0·001) DM intake for treatments MA and HA. Milk yield did not differ between treatments but milk composition was significantly affected by dietary inclusion of algae. Milk fat content was significantly increased (P<0·001) for treatment HA whereas milk protein content was significantly increased (P<0·001) for all treatments containing algae. Milk from treatments LA, MA and HA was significantly enriched in the following PUFA: C20[ratio ]5 (n-3) (0·4–2·1%), C22[ratio ]5 (n-6) (0·8–4·1%), C22[ratio ]6 (n-3) (4·3–12·4%) (P<0·001) and C22[ratio ]5 (n-3) (2·1–3·1%) (P<0·05), which were not detected in control milk. Feta cheese and yogurts produced from the enriched milk had identical composition with the milk, and would be characterized as healthy foods. The ratio of n-6 to n-3 fatty acids was 2·5–4·5.

During the last two decades the traditional subjective appraisal of the body fat stores in farm animals, made by eye and touch, has been rationalized by the introduction of numerical systems of rating specific anatomical points.

Palpation of the lumbar vertebrae, the pin and hook bones (tail head) (Lowman et al. 1973), and, occasionally, width behind the shoulders (Treacher et al. 1986) provides an assessment of the fatness of the animal. This is calibrated from standard photographic charts, in the use of which the operator is trained. Body condition scoring (CS) by this method has been widely developed for dairy cows (Earle, 1976; Mulvany, 1977; MacCarthy, 1978; Scott & Smeaton, 1980; Wildman et al. 1982; Aalseth et al. 1983; Anon. 1986; Garcia Paloma, 1990).

The actual numerical scales have varied among systems. Thus over the range from very thin to very fat cows the scale is 1, 2…7, 8 (Earle, 1976) and 0½, 1,…4½, 5 (Mulvany, 1977), for example. CS is thus a discrete variate with a limited number of readings. Several authors have sought to decrease the division size, for example 1, 1 1/3; 1 2/3;…4 2/3, 5 (Ducker et al. 1985a, see also Dewhurst et al. 1996) and by using the means of the separate values obtained by two operators judging CS independently (W. H. Broster, V. J. Broster, A. J. Clements, J. W. Siviter and T. Smith, unpublished results). In this review CS will be stated in the units given by Mulvany (1977), to which other ranges have been scaled. Inspection of CS data has usually been conducted by analysis of variance, but also by the Mann–Whitney signed rank test (Moorby et al. 1996).

Evans (1978) and Nicoll (1981) studied the variation in recording CS. Both investigators concluded that a system of observation by two independent assessors per recording occasion is advantageous and that revision training is necessary to maintain operator standardization. Of total variance in CS, some 60–70% was found attributable to ‘between-animal’ differences, <5% to assessor variation and <10% to animal×assessor variation. Croxton & Stollard (1976) found good repeatability of CS measurements ‘between’ and ‘within’ operators. It is regrettable that few reports of experimentation give full details of method of and number of operators engaged in body score recording.

The nature of the αs-casein complex of bovine milk has been investigated by cation-exchange chromatography on columns of sulphoethyl Sephadex C-50 of purified preparations of αs-casein and of whole acid-precipitated casein. Three main fractions were separated from each. Two behaved as single homogeneous proteins as judged by starch-gel electrophoresis; they were the main constituent of the complex, αs1-casein, and a closely related phosphoprotein, designated αs0-casein, which was present in small amounts only. The third fraction also constituted only a small part of the total complex. It was heterogeneous on starch gel electrophoresis and contained 2 major and 2 minor components. This fraction, while similar to other members of the αs-casein complex and to β-caseins hitherto described in that it contained phosphorus, nevertheless differed significantly from these since 3 at least of its components contained sulphur either in the form of disulphide bonds or of sulphydryl groupings.

Information is presented on the composition of the 3 fractions including C-terminal end group analysis.

Current trends in the global milk market and the recent abolition of milk quotas have accelerated the trend of the European dairy industry towards larger farm sizes and higher-yielding animals. Dairy cows remain in focus, but there is a growing interest in other dairy species, whose milk is often directed to traditional and protected designation of origin and gourmet dairy products. The challenge for dairy farms in general is to achieve the best possible standards of animal health and welfare, together with high lactational performance and minimal environmental impact. For larger farms, this may need to be done with a much lower ratio of husbandry staff to animals. Recent engineering advances and the decreasing cost of electronic technologies has allowed the development of ‘sensing solutions’ that automatically collect data, such as physiological parameters, production measures and behavioural traits. Such data can potentially help the decision making process, enabling early detection of health or wellbeing problems in individual animals and hence the application of appropriate corrective husbandry practices. This review focuses on new knowledge and emerging developments in welfare biomarkers (e.g. stress and metabolic diseases), activity-based welfare assessment (e.g. oestrus and lameness detection) and sensors of temperature and pH (e.g. calving alert and rumen function) and their combination and integration into ‘smart’ husbandry support systems that will ensure optimum wellbeing for dairy animals and thereby maximise farm profitability. Use of novel sensors combined with new technologies for information handling and communication are expected to produce dramatic changes in traditional dairy farming systems.

Cathepsin D is an indigenous aspartic proteinase in bovine milk. By competitive enzyme-linked immunosorbent assay the amount of immunoreactive cathepsin D and procathepsin D in bovine skim milk was estimated to be 0·4 μg/ml. Immunoreactive cathepsin D purified from whey consisted of a small fraction of mature cathepsin D, but the major form was the proenzyme procathepsin D. A preparation of bovine milk procathepsin D was, like mature cathepsin D, able to degrade purified αs1-, αs2-, β- and κ-casein and α-lactalbumin, while β-lactoglobulin was resistant to cleavage. The cleavage sites in these proteins were determined and compared with those of chymosin. Cathepsin D was capable of generating the αs1-I, β-I, β-II and β-III fragments originally described from the action of chymosin on the respective caseins, and these fragments were subjected to further proteolysis. Cathepsin D was also able to liberate the caseinomacropeptide from purified κ-casein, and to coagulate bovine skim milk. This demonstrated that milk contains an indigenous coagulation enzyme present mainly in the whey fraction.

The principal chemical components of milk from the Arabian camel (Camelus dromedarius) were monitored in Jordan over one year. The analyses included total solids, fat, protein, vitamins, minerals and organic acids. Large seasonal variations in total solids and fat were apparent, with maxima in mid-winter of 139 and 39·0 g/l, respectively, and minima in August of 102 and 25·0 g/l. These differences may be sufficient to alter the sensory properties of the milk, and the fat: casein ratio may need standardisation for cheesemaking. The mean values of trace elements like zinc (5·8 mg/l), iron (4·4 mg/l) and manganese (0·05 mg/l) in Jordanian camel milk could provide valuable additions to the diet of urban populations, as could the mean concentration of vitamin C (33 mg/l). The levels of organic acids were generally higher than in bovine milk and, as with all the constituents of the milk, there were discernible patterns linking concentration and season of the year.

Systematic factors affecting the activities of L-lactate dehydrogenase (LDH) and N-acetyl-β-D-glucosaminidase (NAGase) and somatic cell count (SCC), the association between the activities of LDH and NAGase and SCC with respect to udder health status, and the ability of LDH and NAGase to classify cows in udder health categories for early detection of mastitis were studied. A dataset of records from 74 Danish Holstein, 76 Danish Red and 47 Jersey cows on one research farm was used. Cows were grouped into healthy and clinically mastitic. A healthy cow was defined as having no veterinary treatment and SCC<100000 cells/ml. A clinically infected cow was one receiving veterinary treatment after showing clinical signs of mastitis and SCC >800000 cells/ml. Breed, month of production, and days in milk significantly influenced (P<0·001) LDH activity, NAGase activity and SCC in both healthy and clinically mastitic cows. In healthy cows, LDH activity, NAGase activity and SCC started at a high level immediately after calving and decreased to low levels approximately 30–40 d post partum. All the three parameters increased due to clinical mastitis. NAGase activity had numerically higher variation in healthy cows than in clinically mastitic cows (CV=56·2% v. CV=53·5%). The relationship between LDH activity and SCC was stronger in milk from clinically mastitic than from healthy cows (r=0·76 v. r=0·48 and r=0·67 v. r=0·44 for correlation of observed values and residuals, respectively). LDH activity had higher sensitivity than NAGase activity (73–95% v. 35–77%) while specificities were in a similar range (92–99%). Further, sensitivities for LDH activity were more robust to changes in the threshold value than those for NAGase activity. Opportunities for automated, in-line real-time mastitis detection are discussed.

A total of 169 Lactobacillus strains from 12 species (Lb. acidophilus, Lb. brevis, Lb. buchneri, Lb. casei, Lb. delbrueckii subsp. bulgaricus, Lb. delbrueckii subsp. delbrueckii, Lb. delbrueckii subsp. lactis, Lb. fermentum, Lb. helveticus, Lb. paracasei subsp. paracasei, Lb. plantarum and Lb. rhamnosus), isolated from raw milk and various milk products, and 9 Lactococcus lactis strains were evaluated for peptidase activities with five chromogenic substrates and a tryptic digest of casein. Within each species, the peptidase activity of the cell-free extracts of the strains varied. Furthermore, differences were observed between the Lactobacilhis species and Lc. lactis. Lb. helveticus had by far the highest hydrolysing activities towards all substrates, indicating the presence of powerful aminopeptidases, X-prolyl-dipeptidyl aminopeptidases and proline iminopeptidases. Lb. delbrueckii subsp. bulgaricus possessed high hydrolysing activities towards substrates containing proline, alanylprolyl–p–nitroanilide and prolyl–p–nitroanilide. On the other hand, Lb. fermentum and Lb. brevis could be considered as weakly proteolytic species. A more detailed study with highly proteolytic Lactobacillus strains indicated that at least three different proteinases or endopeptidases were present. Compared with Lc. lactis, the Lactobacillus strains had a much lower hydrolytic action on glutamyl-glutamic acid, suggesting that glutamyl aminopeptidase was absent in lactobacilli.