The objective of this study was to determine the effects of supplementing the diets of dairy cows with Ca soaps of rapeseed fatty acids (CSRFA) and rumen-protected (RP) methionine on their milk yield and composition, including milk protein fractions and fatty acids. Twelve Polish Red Lowland cows were used in a complete balanced two period changeover experiment. The four treatment diets were a control consisting of a total mixed ration of grass silage and concentrates, and the total mixed ration supplemented with RP methionine, CSRFA or RP methionine plus CSRFA. Dry matter intake was not affected by diet. Milk yield increased when cows were given the diet with CSRFA, but supplementation of diets with RP methionine did not affect milk yield. Milk protein content, but not milk protein yield, decreased when CSRFA was given. The addition of RP methionine to the control diet and the CSRFA diet produced similar increases in the milk protein content. Supplementation of the diet with CSRFA significantly changed the milk fatty acid profile: the proportions of 10:0, 12:0, 14:0, 15:0 and 16:0 in milk fat decreased, but those of 18:0 and cis-18:1 increased. We conclude that CSRFA can be used in practical dairy diets to increase milk yield and manipulate its fatty acid composition.

Three groups of 12 lactating Comisana ewes were housed in separate rooms of the same building that contained straw-bedded pens with total areas of 12, 18 and 24 m2. The ewes were assigned to groups with different stocking densities: high (HSD, 1 m2/animal), medium (MSD, 1.5 m2/animal) or low (LSD, 2 m2/animal). The LSD treatment resulted in lower air concentrations of total microorganisms and coliform bacteria than the other two. Ewes in the LSD group gave greater yields of milk, total protein and fat than those in the other two groups. LSD treatment increased milk casein content and improved clotting time and clot firmness. LSD also resulted in ewes giving milk with lower somatic cell counts and smaller concentrations of mesophiles, psychrotrophs and faecal coliforms than MSD and HSD. Subclinical mastitis occurred in three ewes of the MSD group and four ewes of the HSD group, while no cases were recorded in the LSD group. These results indicate that stocking density is a critical factor in dairy sheep housing and suggest that a space allocation <2 m2/animal may adversely affect the performance and health of the lactating ewe.

The distribution of Staphylococcus aureus within herds seems to be related to interactions among the shedding characteristics of the bacteria, their pathogenicity and mammary gland immune status. The aim of the present study was to investigate the relationships between selected mammary gland immune factors and intramammary infections associated with Staph. aureus. Overall, 70 cows from five commercial dairy herds were included in the study and quarter milk samples were assessed using bacteriological and cytological tests. We evaluated differential cell count, lysozyme concentration, N-acetyl-β-glucosaminidase (NAGase) activity, cell viability and respiratory burst activity in randomly chosen quarter milk samples from each cow. Staph. aureus intramammary infection elicited different responses in the mammary gland immune defences investigated. Polymorphonuclear leucocytes (PMN) as a proportion of total somatic cells in milk, cell viability and NAGase activity were higher in infected quarters, while the proportions of macrophages and lymphocytes, respiratory burst activity and lysozyme levels were lower. Mean values differed among herds, but the differences were not significant. These changes were associated with Staph. aureus infection. The reduced respiratory burst activity together with the increase in the proportion of PMN suggests that both the number and activity of PMN could influence the susceptibility of the mammary gland to pathogens. Indeed, the logistic model adopted suggests that impairment of milk immune factors could be concurrent with the development of an infection.

Changes in the contents of retinol, α-tocopherol and β-carotene in plasma, milk and milk fat from 38 Holstein–Friesian cows were followed during their first lactation, and the quantitative and kinetic relationships for secretion of α-tocopherol and β-carotene from blood into milk were determined. The cows were assigned to three groups such that all cows in the same group had the same sire. Milk yield and milk fat content differed with stage of lactation, but not according to sire. The plasma concentrations of retinol, α-tocopherol and β-carotene differed with stage of lactation; in addition, retinol and β-carotene concentration also differed according to sire. The concentrations of all three vitamins in milk and milk fat differed according to sire and stage of lactation. Furthermore, the total secretion of retinol, α-tocopherol and β-carotene into milk (expressed as mg/d) differed with sire and stage of lactation. The quantitative secretion of α-tocopherol and β-carotene from blood into milk followed Michaelis–Menten kinetics for active transport across membranes. Values of maximum secretory capacity Vmax and the half-rate constant Km for both α-tocopherol and β-carotene varied according to sire. Overall means for Vmax for α-tocopherol and β-carotene were 32·4 and 27·5 mg/d. Thus, the daily secretion of α-tocopherol and β-carotene is limited in quantity, and is independent of the yields of milk and milk fat. It follows that continuing breeding and management systems that focus solely on increasing milk and milk fat yield will result in a steady dilution in the milk fat of these vitamins and antioxidants important for the immune defence of the cows and oxidative stability of milk products. The genetic variation found offers the possibility of utilizing these variations in breeding systems.

Associations among quantities and concentrations of individual milk proteins and fatty acids were determined in individual milk samples from 233 Holstein cows. Correlation coefficients among the six major proteins and the eleven major fatty acids in bovine milk were grouped hierarchically. Factor analyses grouped the milk components into seven families: fatty acids 4:0–6:0, 6:0–16:0, 16:0, 18:0, 16:1 plus 18:1 plus 18:2, all milk proteins and β-lactoglobulin alone. Correlation coefficients and groupings by factor analyses coincided with shared pathways of synthesis or genetic origins of milk proteins and fatty acids because they are the basis of the correlation coefficients. Hence, the results from correlations and factor analyses could be used to develop hypotheses for the synthesis of milk components and other coordinately regulated physiological processes.

Quantification of β-lactoglobulin A and B in the milk of heterozygous animals has revealed a differential content of these two variants. Nucleotide sequence analysis of the first 733 bp of the bovine β-lactoglobulin promoter has indicated the presence of ten polymorphic sites, nine of them being allele A and B specific mutations. To study the differential expression of these alleles, constructs containing 753 bp long fragments of the bovine β-lactoglobulin A and B associated promoters were used in transient transfection experiments in HC11 cells. A differential transcription activity directed by the A and B specific promoters was consistently observed. The relative expression levels were 57% for β-lactoglobulin A and 43% for β-lactoglobulin B promoters. An allele-specific mutation has been reported to have a differential binding affinity to the activator protein-2 between the β-lactoglobulin A and B promoters. However, experiments in HC11 cells where the activator protein-2 binding sites were mutated in both β-lactoglobulin A and B promoters showed no major differences in activity between the mutated and native promoters.

β-Lactoglobulin (β-lg) in aqueous solution under pressure showed a marked depolarization of intrinsic fluorescence assigned to a gradually increased rotational diffusion of tryptophyl moieties in pressure-unfolded states. The corresponding change in anisotropy provided a new and more accurate method for determining denaturation volume which, for β-lg in neutral aqueous solution with ionic strength 0·16 (NaCl) at 25 °C, was ΔV°=−73 (SE 3) ml mol−1, corresponding to half denaturation at 123 MPa. The pressure unfolding led to exposure of hydrophobic regions to the protein–water interface that could be probed by fluorescence intensity of a β-lg–1-anilinonaphthalene-8-sulphonic acid (ANS) complex with 1:1 stoichiometry, as determined by Job's method of continuous variation. The unfolding of β-lg impaired the binding capacity of the inner calyx, with a reduction in binding capacity of 50% at 50 MPa, as shown by decreasing cis- parinaric acid fluorescence, decreasing anisotropy and decreasing radiationless energy transfer from tryptophans to this probe with increasing pressure. The pressure-induced reversible exposure of hydrophobic groups to the protein–water interface may, at least partly, explain the initial aggregation reactions, evident from increased Rayleigh scattering from ∼50 MPa, prior to irreversible pressure-induced gel formation of β-lg. Using results from this and previous studies, we propose a three step pressure denaturation model for β-lg for neutral solution at ambient temperature, including an initial pressure-melted state (up to 50 MPa) with partial collapse of the inner calyx and solvent exposure of the free thiol group, followed by a reversible denaturation with exposure of hydrophobic regions (half denaturation at 123 MPa) and with irreversible denaturation with thiol–disulphide exchange becoming increasingly important at higher pressures. Effects of pressure on β-lg, as measured by fluorescence depolarization, were found for the reversible denaturation steps to be similar to the effects of chemical denaturants but different with respect to shift in ANS emission maxima.

The anti-colon cancer effect of dietary fibre results in part from its fermentation into the short-chain fatty acid butyric acid (BA) by intestinal microflora. BA has potent anti-colon cancer properties owing to its ability to induce apoptosis in colon cancer cells. The colon is not the only location where BA may reach high concentrations, because dietary BA is rapidly absorbed and transported to the liver. We have investigated whether BA could induce apoptosis in transformed human liver (Hep G2) cells. Hep G2 cells treated with BA displayed acetylated histones, increased DNA fragmentation and morphological features consistent with apoptosis. These biochemical features of BA-treated liver cells are identical to those of BA-treated colon cells. In addition, we investigated whether BA present in tributyrin, a triacylglycerol more compatible for inclusion into colloidal lipid structures than BA, could also induce apoptosis in Hep G2 cells. Tributyrin induced DNA fragmentation and morphological features characteristic of apoptotic cells in Hep G2 cells. These results are a significant advance towards delivering BA via colloidal lipid particles to cancerous sites in vivo. This study showed that BA and tributyrin are potent apoptotic agents, and we suggest that sources of dietary BA, such as milk fat, may provide anti-liver cancer properties.

We have studied the contents of trace elements of nutritional or toxicological interest in 90 samples of whole, low-fat, skim, condensed, evaporated and powdered milks. Slurries of the samples were prepared with Triton X-100 and analysed using electrothermal atomic absorption spectrometry. The temperature–time programme of the graphite oven was optimized for each element, and the accuracy, precision, selectivity and sensitivity of the method were verified. Concentrations of the trace elements we investigated were: Pb 0–0·211 μg/g, Cd 0–28·985 ng/g, Al 0·528–4·025 μg/g, Cu 0·041–0·370 μg/g, Cr 0–0·177 μg/g, Mn 0·024–0·145 μg/g, Se 0–237·333 ng/g, Zn 0·297–0·827 μg/g and Ni 0·058–1·750 μg/g. (A value of zero indicates that the element was undetectable by our methods.) Concentrations of the pairs of elements Cu–Cd, Mn–Cd, Mn–Cu, Zn–Mn, Ni–Cu, Ni–Mn and Ni–Zn were significantly correlated (P<0·001). Linear discriminant analysis confirmed the separation between the six types of milk analysed.

A study was undertaken to compare the chemical and sensory characteristics of Abondance cheeses made with milk from animals grazing areas within the same highland pasture, but with different predominant plants. Nine cheeses made during the last 3 d of three successive 7 d periods were evaluated. The animals grazed on the southern side of the highland pasture during the first period (15–21 June), on the northern side during the second period (22–29 June) and returned to the southern side for the third period (30 June–6 July). The gross composition of the cheeses did not vary between periods. ‘North’ cheeses contained more plasmin, γ-casein, αs1-I-casein and water-soluble N than ‘south’ cheeses. Both sensory and instrumental measurements indicated that north cheeses were less firm, stickier and more easily fractured than south cheeses. North cheeses were also more salty, bitter and persistent. Their overall aroma was more intense and they had more intense sour, burnt, toasted, fermented vegetable and sweat aromas, but less intense toffee, exotic fruit and acid milk aromas. The texture differences noted between the cheeses from milk produced on the two areas may come from differences in primary proteolysis, partly due to different amounts of plasmin and plasminogen in milk and in cheeses. The aroma differences were related to differences in volatile compounds. Some compounds had a microbial origin, while some others may have come from the pasture.

The concentration ranges in milk and cheese of a number of metallic elements relevant to the health of the consumer are dependent upon animal species, feeding, time of year, environmental conditions and manufacturing processes. We have measured the concentrations of selected trace elements – Al, Ba, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Pt, Sr and Zn – in raw ewes' milk and typical ewes' milk cheeses. Samples of milk, curd, whey, cheese after moulding, cheese after salting, commercial cheese (Pecorino), Ricotta, scotta and brine were analysed for seven complete cycles of cheese production. Samples of curd, whey, brine and waste product (i.e. scotta) were collected and analysed in addition to the cheese and milk to assess the distribution of each element in the main product, by-products and waste products during cheesemaking. Quantitative determinations were performed mainly by inductively coupled plasma atomic emission spectrometry. There were considerable differences among the trace element contents of raw ewes' milk and related products, indicating that manufacturing processes play a key role in the distribution of minor and trace elements. Two different approaches were used to assess the dietary intake of these elements associated with the consumption of Pecorino and Ricotta, and whether this had any nutritional or toxicological implications. The results indicated no toxicological risk and showed that, on the contrary, Pecorino may be a good source of several essential elements.

The light stabilities of two commercial colorants for Cheddar cheese, an annatto extract and a β-carotene preparation, have been compared in a model system and tested in industrial scale production. The apparent quantum yields for photodegradation by monochromatic light were determined at 25 °C for solutions of the colorants in air-saturated 10 mm-citric acid–disodium hydrogen phosphate buffer containing 100 mg sodium caseinate/l at pH 5·2 and 5·4. Solutions of commercial β-carotene were more photostable than solutions of annatto, and although the quantum yields for photodegradation for both solutions depended significantly on both pH and irradiation wavelength, exposure to u.v. light (313 and 366 nm) caused more photobleaching than exposure to visible light (436 nm). The differences in colour stability observed in the model system were verified by tristimulus colorimetry during 9 weeks illuminated storage at 5 °C of Cheddar cheese produced from milk to which had been added (per 1000 kg) 67 g β-carotene extract or 133 ml annatto.

The sensory and rheological characteristics of stirred yogurts varying in fermentation temperature, heat treatment of milk, dry matter content and composition of bacterial cultures were investigated. Two independent sensory properties, non-oral viscosity and oral viscosity, were evaluated. To reflect these properties precisely it was necessary to perform rheological measurements at both small and large deformations. Non-oral and oral viscosities were successfully modelled from a set of rheological variables by partial least squares regression, resulting in a three component model explaining 83·8% of the variation in non-oral viscosity and a two component model explaining 82·0% of the variation in oral viscosity. Non-oral viscosity was highly correlated with the complex modulus (G*) from the dynamic oscillatory measurements (r=0·823) and the viscosity obtained from a Brookfield viscometer (with Helipath stand) operating at 5 rev./min (r=0·862). Similarly, there were relationships between oral viscosity and the hysteresis loop area from the viscometry test (r=0·867) and between oral viscosity and the viscosity obtained from the Posthumus funnel (r=0·834).

The casein micelles of bovine milk are large aggregates of roughly spherical shape consisting of the four phosphoproteins αs1-, αs2-, β- and κ-casein (CN). They are polydisperse colloidal particles with weight-average diameters between about 50 and 500 nm (Horne, 1984). Since αs1-, αs2- and β-CN are sensitive to calcium it is assumed that they are located predominantly within the micelle, whereas κ-CN is mainly on the surface of the micelles and serves as a stabilizer for the aggregates owing to its hydrophilic C-terminus. Inorganic calcium phosphate interacts with the phosphate groups of the caseins. This conformation of caseins, calcium and phosphate also contains small amounts of magnesium and citrate. Of the dry matter of the micelle, ∼93% is casein and ∼7% inorganic components, mainly calcium and phosphate (McMahon & Brown, 1984; Holt & Horne, 1996).

In several studies it has been demonstrated that milk with the κ-CN B variant has on average smaller micelles than κ-CN A milk (Morini et al. 1975; Nuyts Petit et al. 1997). Compared with κ-CN variants, there are only a few studies on the association of αs1-, αs2- and β-CN variants with casein content and micelle size. In the milk of β-casein-deficient mice, casein micelles were smaller than in normal mouse milk but still present. The lack of β-CN was partly compensated by an increased whey protein content (Kumar et al. 1994). A comparison of the cheesemaking properties of Tarentaise milks containing the A (A1 or A2, without distinguishing between these variants) and C variants of β-CN revealed that the most significant characteristic for discriminating the two types of milk is the average diameter of the casein micelles: 293 nm in β-CN C type milk, 187 nm in the A type (Delacroix-Buchet & Marie, 1994).

The objective of the present study was to investigate the micelle size and the casein composition of milk from half sibs within Simmentals cross bred with Red Holsteins (Simmentaler Fleckvieh, SI×RH) sires heterozygous for A1A2 of β-CN.

Enumeration of bacteria in raw milk is of public health and economic importance. Among the proposed rapid methods for assessment of bacterial contamination in raw milk, ATP bioluminescence has proved to be one of the most promising (Griffiths, 1991). Several companies produce ATP bioluminescence reagent kits and equipment for analysing raw milk samples for total bacterial count (Sutherland et al. 1994; Reybroeck & Schram, 1995). The principle of ATP bioluminescent bacterial assay is based on the following assumptions (Olsen, 1991). All living organisms contain ATP, ATP is neither associated with dead cells nor absorbed on to surfaces, colloids and so on, and there is a fairly constant ratio of ATP to biomass/number of cells for all microbial taxa independent of metabolic activity or environmental conditions. Of these assumptions, only the first seems to be indisputable. It is not the number of bacterial cells, but rather the colony forming unit (cfu) that is the denomination used when assessing the microbial quality of milk. For Gram-negative rods of the genus Enterobacteriaceae, a cfu is usually derived from a single cell. However, Gram-positive cocci (staphylococci and streptococci) grow in bunches and chains respectively (Gregg, 1991), and estimation of cell numbers may not give good agreement with the colony counts.

Several approaches have been investigated to increase the sensitivity of the bioluminescent method (Pahuski et al. 1991; Sutherland et al. 1994; Reybroeck & Schram, 1995; Froundjian et al. 1999). Although the detection limit achieved by these modifications (104 cfu/ml) may be sufficient for practical use (Bautista et al. 1992; Reybroeck & Schram 1995), the accuracy of the analysis was not significantly improved. The reported values for accuracy of the estimate for cfu/ml in raw milk (Syx) by the bioluminescent method were in the range 0·27–0·87 log units (Bautista et al. 1992; Reybroeck & Schram, 1995). The purpose of the present study was to determine the reasons for the lack of accuracy of the bacterial ATP assay in raw milk.

D-alanine (D-Ala), D-aspartic acid (D-Asp) and D-glutamic acid (D-Glu) are important constituents of the cell walls of bacteria responsible for fermentation processes, and have been detected in several fermented foods, such as cheeses, yogurt and vinegar (Palla et al. 1989; Brückner & Hausch, 1990; Dossena et al. 1991; Brückner et al. 1992; Gandolfi et al. 1992). In particular, D-amino acids have been found, free and abundant, in cheeses requiring long ripening periods (1–2 years; Santaguida et al. 1995). Their presence in cheeses could be related mainly to lysis of the bacterial wall, to which short-chain D-amino acids are bound, but also to the activity of bacterial racemases (Adams, 1972), which convert free L-amino acids generated during proteolysis. The content of these D-amino acids and the D:L ratio have been recently proposed as indicators of ripening and for quality assessment of Parmigiano Reggiano and Grana Padano cheeses (Marchelli et al. 1997).

The aim of the present study was to determine D-amino acids in cheeses with shorter ripening periods to evaluate whether they could be useful as indicators of ripening and for quality assessment. The work was carried out with Montasio, a typical cheese produced in north-east Italy using traditional methods. Montasio is a semi-hard cheese produced from unpasteurized milk, cooked at 44–46 °C and consumed after at least 2 months ripening. This study represents an extension of previous work on free amino acid contents and ripening in semi-hard cheeses (Innocente, 1997).