The aim of the study was to establish in vitro a bovine mammary epithelial cell (MEC) clone, able to respond to mitogenic growth factors and to lactogenic hormones. Mammary tissue from a 200-d pregnant Holstein cow was used as a source of MEC, from which a clone was established through a process of limiting dilution. When plated on plastic, the cells assumed a monolayer, cobblestone, epithelial-like morphology, with close contact between cells. Inclusion of IGF-1 and EGF in the media significantly increased the number of cells 5 d after plating. All cells stained strongly for cytokeratin and moderately for vimentin at young and old passage stages, indicating the epithelial nature of this cell clone. When the cells were plated at a high density on a thin layer of a commercial extracellular matrix preparation (Matrigel), lobular, alveoli-like structures developed within approximately 5 d, with a clearly visible lumen. When cells were plated onto Matrigel in differentiation media (containing lactogenic hormones), detectable quantities of α-casein were present in the media and particularly on the lumen side of the structures. Omission of one of the lactogenic hormones (insulin, prolactin or hydrocortisone) reduced α-casein release to the limit of detection of the assay used. Lactoferrin was also produced when the cells were plated on Matrigel, again principally on the lumen side of the lobules, though this was independent of the lactogenic hormones. By passage 40, the cells had senesced, and it was not possible to induce α-casein or lactoferrin production. This study notes the establishment of a functional bovine mammary epithelial cell clone, which is responsive to mitogenic and lactogenic hormones and an extracellular matrix.

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.

The objective was to determine the effect of once-daily milking (ODM) and omitting one evening milking each week (13TWM), in late lactation on milk production, composition and processability. Seventy-two cows were assigned to three treatments (ODM, 13TWM and twice-daily milking [TDM]) from 4 October to 12 December. Cows were on average 218 d into lactation at the start of the trial, and all cows were managed similarly throughout the trial. Milk yields and gross milk composition of cows on all treatments were measured, and milk samples for detailed compositional and processability analysis were collected from TDM and ODM treatments at two consecutive milkings and at one milking each week, respectively. Milk yield was significantly reduced (P<0.001) and milk fat and protein concentrations were increased (P<0·01) with ODM compared with TDM. Milk yield and fat and protein concentrations of milk from TDM and 13TWM herds were similar. Casein concentrations in ODM and TDM milks were similar, but ODM milk had a higher (P<0·05) whey protein content. Somatic cell count of ODM and TDM milks was similar. Rennet coagulation time (RCT) and curd firmness (A60) of milk were not affected by milking frequency. However, rate of curd aggregation (K20) of ODM milk was reduced (P<0·05) compared with that of TDM milk. Plasmin activity in ODM milk was numerically higher than in TDM milk, but the effect was not significant. ODM milk had higher NAGase activity than TDM milk (P<0·01). In conclusion, once daily milking reduced milk yield by 29% and did not adversely affect the processability of milk. Moreover, one evening milking per week could be eliminated without adverse effects on milk yield or composition.

Milk from dairy cows never known to have had an intramammary infection with Streptococcus uberis can inhibit growth of Str. uberis for up to 7 h. This inhibition is abolished if milk is heated to 80 °C. Inhibition appears not to be related to immune defences as it occurs in skimmed milk (cell free), is unrelated to the concentration of immunoglobulin and survives heating to 56 °C. The effect is partly overcome by addition of selected amino acids and vitamins. It is suggested that the inhibition is caused by a restriction in the supply of essential nutrients part of which may require the conversion of plasminogen to plasmin.

To establish whether fishy off-flavour observed in cows' milk in Sweden is due to abnormal concentrations of trimethylamine (TMA) in milk, 15 milk samples from 13 cows of the Swedish Red and White breed (SRB) were analysed for this compound using dynamic headspace (DHS) gas chromatography (GC). A mass selective detector (MSD) was used for the qualitative and a flame ionization detector (FID) for the quantitative analyses. Further confirmation was obtained using a solid phase microextraction (SPME) followed by GC-olfactometry (GC-O) and GC-NPD (nitrogen and phosphorus detector). Samples were also evaluated by a two-person organoleptic panel for the presence of fishy off-flavour. Results showed that the seven milk samples with a fish-like taint contained >1 mg TMA/kg milk, whereas, with a single exception, the seven samples that were judged to be normal did not contain this compound. Furthermore, there were indications of a dose-dependent relationship between TMA concentration and fishy off-flavour score.

Colostrum and milk samples from 20 goats were analysed for concentrations of immunoglobulin G (IgG), β-lactoglobulin (β-lg), α-lactalbumin (α-la) and serum albumin (CSA) throughout the first 14 milkings post partum (7 d of lactation) using single radial immunodiffusion assay. Concentrations (mg/ml, means±SD) at first milking were IgG 47·9±25·5, β-lg 30·7±10·4, α-la 2·77±0·82 and CSA 2·97±2·46 mg/ml. Large variations were recorded for IgG concentrations (19·9–94·5 mg/ml) and β-lg (9·3–49·8 mg/ml). Concentrations of IgG, β-lg and CSA dropped abruptly in the subsequent milkings and α-la concentration decreased slowly. Mean IgG concentration was <2 mg/ml after 7 milkings and <1 mg/ml after 11 milkings. However, IgG concentration does not differ significantly, at the 1% level, from milkings 7–14. The contribution of β-lg to the increase in whey proteins in early milks was greater than that of IgG from milkings 5 to 14. The results were tabulated to make it possible to calculate the excess of whey proteins that would be obtained if early milks were illegally added to milk supply.

Lactoperoxidase activity and thiocyanate content were monitored in the milks of seven individual cows and six goats during lactation. Lactoperoxidase activity exhibited a cyclic pattern with alternating peaks and troughs throughout lactation. Extremely large variations were observed between and within animals. For example, lactoperoxidase activity ranged from 0·05–5·60 U/ml for one cow on different sampling days. Variations between cows were also large, ranging from 0·98–5·1 U/ml on a specific sampling day. Mean lactoperoxidase activity in cows ranged from 1·5–2·7 U/ml with an overall mean of 2·3±1·0 U/ml while the thiocyanate concentration ranged from 6·0–10·2 μg/ml with an overall average of 8·5±5·1 μg/ml. Lactoperoxidase activity means for goats ranged from 0·04–0·16 U/ml with a grand mean of 0·1±0·06 U/ml while the thiocyanate content means ranged from 6·6–8·2 μg/ml with a grand mean of 7·0±2·59 μg/ml. There was no correlation between lactoperoxidase activity and thiocyanate content in either cows' (R2 = 0·011) or goats' (R2 = 0·015) milk. These experiments have revealed that lactoperoxidase activity is affected by many factors including the individual animals, species, feed and stage of lactation. Therefore the exogenous supply of thiocyanate and hydrogen peroxide needed to activate the lactoperoxidase system for raw milk preservation will vary in quantity depending on these factors.

The relative proportion of caseins to total protein is a parameter that can be used to control the protein quality in standardised milk, an increasing tendency in dairy industries. 31P-NMR was used to analyse the casein content of milk, by the quantitation of the area under the resonances belonging to SerP, and using methylenediphosphonic acid as internal standard. This procedure yielded good results, as similar values of caseins were obtained from N Kjeldahl and NMR analysis for slightly heated milk samples. Heating at 95 °C for 15 min did not alter the casein content results. Casein content of raw, pasteurised and UHT milks (25·6±1·4, 26·4±1·8, 25·5±1·6 g casein/l milk, respectively), obtained by NMR, were not significantly different, giving an average of 25·8±1·6 g casein/l for bulk liquid milk. This work concluded that 31P-NMR could be used as an alternative method to determine casein in raw, pasteurised, dry and UHT milks.

Lysozyme from buffalo milk was purified to homogeneity and its N-terminal amino acid sequence, biochemical properties and antibacterial spectrum were determined. The purification procedure, comprising ion-exchange chromatography using CM-cellulose and size-exclusion chromatography using Sephadex G-50, conferred 8622-fold purification and 39·3% recovery of lysozyme. The purified enzyme migrated as a single band on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and native PAGE. Immunological purity of lysozyme preparation was confirmed by immuno-electrophoresis. Molecular weight of buffalo-milk lysozyme as determined by SDS-PAGE was 16 kDa and its amino acid composition was determined by reverse phase high performance liquid chromatography (HPLC). The sequence of 23 amino acid residues at the N-terminal end showed 56·5% homology with bovine milk lysozyme and 30·4% with equine milk lysozyme. The specific activity of buffalo milk lysozyme was ten-times that of bovine milk lysozyme. Buffalo-milk lysozyme was active over a wide range of pH and its activity was strongly influenced by molarity of the medium. Antibacterial activity of buffalo-milk lysozyme was determined against 11 species of bacteria; out of seven Gram-positive bacteria tested, four were inhibited, while Gram-negative bacteria were resistant.

Transglutaminase (TGase) is an enzyme that cross-links many proteins, including milk proteins. In this study, the effects of TGase on some physico-chemical properties of milk were studied. TGase-treated milk was not coagulable by rennet, which was due to failure of the primary (enzymic) stage of rennet action rather than the non-enzymic secondary phase. Dissociation of TGase-treated casein micelles by urea or sodium citrate or removal of colloidal calcium phosphate by acidification and dialysis was reduced, presumably due to the formation of cross-links between the caseins. Casein micelles in TGase-treated milks were also resistant to high pressure treatment and to hydrolysis by plasmin. Results of the present study show that milk proteins are fundamentally modified by the action of TGase, which may have applications in the manufacture of functional proteins for use as novel food ingredients.

The critical flux during ultrafiltration of whey protein concentrate and sodium caseinate suspensions was investigated. The weak form of critical flux was found for both suspensions. Critical flux of sodium caseinate was higher than that of whey protein concentrate. This could be due to the differences in particle size of the suspensions, resulting in a slower particle back transportation for small particles (whey proteins) compared to the larger casein micelles. Critical flux increased as crossflow velocity increased and decreased as concentration increased, suggesting that critical flux was determined by competition between rate of particle removal from the membrane surface and rate of particle movement towards the membrane surface. Influence of changing pH, addition of NaCl and CaCl2 on the critical fluxes of both protein suspensions was also studied. Increasing pH led to an increase in critical flux for both protein suspensions, suggesting that electrostatic repulsive forces are involved in determining critical flux in both cases. Addition of NaCl gave rise to a decrease in electrostatic interactions due to an increase in ionic strength and ζ potential, and resulted in a decrease in critical flux for sodium caseinate, but had no significant effect for whey protein concentrate. Addition of CaCl2 resulted in a decrease in the critical flux and had a more pronounced influence than NaCl. These results suggest that, in addition to electrostatic repulsive forces, other factors such as structure of protein may be involved in determining the critical flux.

Thirty-three Lactobacillus strains were tested as adjuncts in a cheese model system. Eighteen strains originated from cheese (nine Lactobacillus spp. and nine Lb. paracasei/casei) and 15 from human intestinal mucosa (11 Lb. rhamnosus; three Lb. paracasei; one Lb. plantarum). Model cheeses weighing 120 g were made of cheese grains from full-scale production of washed curd semi-hard cheese (Herrgård). The model system was reproducible and similar to full-scale production with respect to moisture, salt content, pH and microbial flora. The model cheeses were sampled for aerobic and anaerobic plate count and viable counts of Lactobacillus and Lactococcus. The presence of adjuncts in the model cheeses was confirmed by typing isolates with Randomly Amplified Polymorphic DNA (RAPD). The sensory properties of model cheeses were described. In a first trial 23 of the 33 adjuncts were re-isolated from the corresponding model cheeses after 9 or 13 weeks. Adjuncts of Lb. paracasei were re-isolated more frequently than adjuncts of Lb. rhamnosus. Nine strains were selected, on the basis of their ability to grow and be a dominating part of the microflora of model cheese with interesting sensory properties. These strains were further studied together with two commercial cultures. The sensory influences on model cheeses of six of the adjuncts were confirmed, and flavour scores were in the range of 2.9–7.1 for model cheeses with different adjuncts while the control had a flavour score of 5.6 (0–10 scale). Survival and growth of seven out of the nine strains correlated with the results of the first trial. Growth and influence on flavour of four adjunct cultures were confirmed in experimental cheese manufactured in a 400-l open vat.

Iron is an essential element for humans and physiological needs are determined by obligatory loss, growth, menstruation and pregnancy. Although iron metabolism occurs in a ‘closed circuit’, physiological losses occur and they must be made good. Three factors are important in the study of iron needs: the total amount of iron in the diet; the nature of the iron compound; and other components of the diet (Hallberg et al. 1998). Although iron de®ciency ensues if insu¾cient iron is absorbed to meet requirement, the total iron absorbed normally exceeds requirement (Hallberg et al. 1997; Jackson, 1997).

Cystic fibrosis (CF) is the most common genetic disease of Caucasians with an incidence of 1 in 2500 live births and a carriage rate of 1 in 20 individuals. CF patients continue to suåer from recurrent and chronic respiratory tract infections and most of their morbidity and mortality is due to such infections throughout their life (Høiby, 1991). These infections are usually dominated by Gram-negative organisms, especially by the pseudomonads including in particular, Pseudomonas aeruginosa, as well as members of the Burkholderia cepacia complex of organisms.

Proteolysis of casein is the principal cause of textural changes and flavour development in ripened cheese (Fox & McSweeney, 1996). Caseins are degraded into small peptides and free amino acids during a complex process, described by Grappin et al. (1985) as a two-step scheme. Caseins are initially broken down into large, well characterised fragments. This initial step, called primary proteolysis, is catalysed principally by the residual coagulant (chymosin and pepsin), and to a variable extent by endogenous milk proteases, such as plasmin, cathepsin D, and possibly somatic cell proteinases. Enzymes originating from either rennet or milk are active in most ripened cheese varieties. However, their relative contributions vary substantially depending on manufacturing practices. For instance, in Swiss-type cheeses, cooking the curd extensively inactivates the coagulant, and simultaneously enhances plasmin activity, which therefore becomes predominant (Ollikainen & Kivela, 1989).