The fatty-acid composition of 17 samples of New Zealand milk fat obtained throughout one dairy season is reported.

The weight percentage of butyric (C4:0) acid was significantly correlated with that of caproic (C6:0) acid and that of caprylic (C8:0) acid. Percentages of C6:0 and C8:0 showed a highly significant correlation with each other and with weight percentages of capric (C10:0) and lauric (C12:0) acids.

There was a highly significant negative correlation between palmitic (C16:0) and stearic (C18:0) acids and between C4:0 and C16:0 acids. Oleic (C18:1) acid showed significant negative correlations with C8:0, C10:0, C12:0, myristic (C14:0) and C16:0 acids.

Deposit formation was measured in a model laboratory plant in which whole milk was in contact with a heated surface at 100 °C for 1 h. The effect of the interfacial properties of various poly mer-coated surfaces on the amount and the adhesion strength of deposit was determined. The nature of the surface influenced the formation of deposit only slightly, but had a large effect on its adhesion strength. From correlation analysis, the polar contribution to surface energy was identified as the main factor influencing the deposit adhesion strength. These results suggest that the type of interactions at the surface govern the ease of removal of deposit.

Lactobacillus helveticus and Propionibacterium freudenreichii are essential starters in Swiss cheesemaking and the release of their intracellular enzymes through autolysis could significantly influence ripening. To provide evidence of this lysis, cheese made from microfiltered thermized milk inoculated with Lb. helveticus ITGLH77, Prop. freudenreichii ITGP23 and a commercial Streptococcus thermophilus was assayed. Starter viability was determined and lysis was monitored during ripening by protein analysis with SDS-PAGE of aqueous cheese extracts and by immunoblot detection of intracellular proteins: dipeptidase (PepD) for Lb. helveticus and methylmalonyl coenzyme A mutase for Prop. freudenreichii. We verified that the species specificity of these lysis markers was towards the cytoplasms of all the species currently used in Swiss cheese. Lb. helveticus exhibited an almost complete loss of viability (99·9%) from the beginning of ripening in the cold room; concomitantly PepD appeared in the cheese extracts and was detected until the end of ripening. Damaged Lb. helveticus cells were also visualized by scanning electron microscopy. In addition, free PepD was also successfully detected in commercial Swiss-related cheeses. All these results clearly demonstrated the autolysis of Lb. helveticus in Swiss cheese. Prop. freudenreichii ITGP23 grew during warm room ripening and no loss of viability was detected after maximal growth (109 cfu/g cheese). Free methylmalonyl-coenzyme A mutase was detected at the end of ripening during cold storage, when the cheese extracts were concentrated 20-fold, demonstrating that the autolysis of Prop. freudenreichii was tardy and limited.

Casein micelle suspensions, colloidal Ca phosphate-free casein solution and simulated milk ultrafiltrate (SMUF) were studied using high-resolution 43Ca and 31P NMR in the temperature range 4–64 °C. Only one 43Ca and one 31P signal was obtained for each solution. Signal intensities and line widths varied with the environment and were affected by the redistribution of Ca and P during heating and cooling. Based upon the temperature-dependent broadening of the 43Ca signal, five different Ca environments were discerned in the heated milk fractions. The Ca state, induced by heating of a casein-containing milk salt solution, differed from both the state of Ca present in micellar colloidal Ca phosphate and from the state of Ca induced by the heating of SMUF.

Casein composition in Friesian herd milks was examined by quantitative column chromatography on hydroxyapatite. Whole casein was resolved into 5 fractions: (1) γ-casein + para-κ-casein; (2) κ-casein + unidentified chymosin-resistant components; (3) unidentified minor protein; (4) β-casein; (5) αs1,0- + minor αs-caseins. Protein in fractions 1, 2, 4, 5 was measured by ultraviolet spectrometry, using appropriate specific absorption coefficients. The quantitative contribution of chymosin-resistant components to the κ-casein fraction was measured by a method involving hydroxyapatite chromatography of chymosin-treated whole casein. Compositional analysis was carried out throughout a lactation cycle on a total of 24 casein samples from the milks of a winter/spring calving and autumn-calving herd. Average composition (expressed as % total casein), which was similar for both herds, was 48·7% αs-, 33·8% β-, 4·9% γ-, 9·5% κ- and 3·2% unidentified components. Lactational effects on composition were also similar for both herds and were most pronounced in late lactation where increases were recorded in γ-casein and unidentified components, and decreases in β- and αs-caseins. Fluctuations in κ-casein proportions were small and slightly higher values were obtained in early and late lactation. Casein composition also appeared to be affected to some extent by season, as shown by differences in the proportions of αs-caseins and unidentified components between mid-lactation milks from the 2 herds. Compositional variations resulted partly from the action of milk proteinase on β-casein and also, apparently, from differences in relative rates of protein biosynthesis.

Fifty-six Holstein dairy cows from a commercial dairy herd in the Northern part of Greece were used to determine the effect of vitamin E supplementation on immune parameters, milk composition and milk quality. Cows were assigned to one of two experimental groups: control (no vitamin E supplementation) and vitamin E supplementation. Supplementation of vitamin E started 4 weeks prior to and continued up to 12 weeks after parturition. Supplementation included daily oral administration of vitamin E at 3000 i.u./cow prepartum and was reduced to 1000 i.u./cow post partum. Blood samples were collected weekly for 8 weeks starting 4 weeks before parturition, neutrophils were isolated and the following parameters were determined in neutrophils activated by phorbol myristate acetate: total cell-associated and membrane-bound urokinase plasminogen activator (u-PA) activity and superoxide production. Milk samples were collected weekly and fat, protein, lactose, somatic cell count (SCC), plasmin and plasminogen-derived activity were determined. Activated neutrophils isolated from cows that received supplemental vitamin E had higher (P<0·01) total and membrane-bound u-PA activities during the first 3 weeks after parturition and higher (P<0·01) superoxide production during week 1 prepartum and week 1 post partum compared with the corresponding values of activated neutrophils isolated from control cows. Vitamin E supplementation had no effect (P=0·28) on plasminogen-derived activity in milk. Milk obtained from cows that received supplemental vitamin E had SCC lower by 25% (P<0·05) and plasmin lower by 30% (P<0·01) than corresponding values in milk obtained from control cows. The reduction in plasmin as a result of vitamin E supplementation is very beneficial to the dairy industry because plasmin reduces the cheese-yielding capacity of milk, affects the coagulating properties of milk and its overall ability to withstand processing during cheesemaking. In conclusion, vitamin E supplementation had positive effects on the function of bovine neutrophils and milk quality in a commercial dairy herd.

A study of the inhibitory action of Debaryomyces hansenii (31 strains) on Clostridium tyrobutyricum (5 strains) and Cl. butyricum (2 strains) on laboratory media showed that Deb. hansenii inhibited the growth of these organisms, and that this effect was due not only to competition for nutrients but also to the production of both extra-and intracellular antimicrobial metabolites. The inhibitory effect varied with strain and occurred whether the yeasts were grown aerobically or under reduced O2 tension.

Ten pregnant heifers were inoculated in both hind udder quarters with a mixture of Actinomyces pyogenes, Fusobacterium necrophorum and Peptostreptococcus indolicus. Development of the experimental mastitis was monitored by sequential clinical and bacteriological examinations, and by blood acute phase protein profiles. Sequential changes in plasma fibrinogen, serum haptoglobin, acid-soluble glycoproteins and α1-proteinase inhibitor activity were analysed and compared with both the clinical and bacteriological findings and the final outcome of the disease after calving. All ten heifers developed moderate to severe clinical mastitis. Four recovered completely, had a normal lactation after calving and exhibited only transient fever and moderate local signs. In six of the heifers the course of the disease was severe, and the inoculated quarters failed to produce milk after calving. The acute phase response of the four heifers that recovered was also significantly milder than that of the other six heifers. Haptoglobin and acid-soluble glycoproteins were most effective in indicating the severity of the infection and predicting the final outcome of the disease. Fibrinogen was a reliable indicator for detecting the presence of bacterial infection in all heifers. α1-Proteinase inhibitor activity was of low diagnostic value in this study.

The reason for the reported difference in spoilage behaviour of skim and whole pasteurised milks was investigated. The rates of growth of psychrotrophic bacteria were not significantly different in the two milks and the bacterial types, all pseudomonads, present at spoilage were also similar. However, when representative spoilage organisms were cultured into freshly pasteurised skim and whole milks, skim milks exhibited predominantly bitter flavours while whole milk showed mostly sour flavours. The different spoilage behaviours can be largely explained by greater proteolysis in skim milk than in whole milk, caused by higher production of protease and greater susceptibility of the protein to protease attack. In addition, lipolysis in whole milk, caused by the substantial quantities of lipase produced by spoilage pseudomonads in this milk, also contributes to the different flavours produced during cold storage of these milk types.

The data presented in this research communication represent the first comprehensive report on the prevalence of udder pathogens and their resistance in Slovak dairy cattle breeds. A total of 633 milk samples from 42 herds were tested. The most frequently isolated pathogens were coagulase negative staphylococci CNS or non-aureus staphylococci (NAS) followed by Escherichia (E.) coli, Staphylococcus (S.) aureus, Streptococcus (Str.) uberis and Streptococcus (Str.) agalactiae. Generally, isolated pathogens showed common resistance to aminoglycosides (streptomycin, neomycin), which are the most commonly used antibiotics to treat mastitis in Slovakia.

1. Detailed analyses for the major constituents of the colostrum and milk of four sows are reported. In all cases the initial colostrum is characterized by a very high protein, and a low lactose and fat content. As with the colostrum of other species, the transition to milk occurs progressively during the course of about 4–7 days.

2. Analyses for mineral constituents, calcium, magnesium, phosphorus and chloride are reported on a range of samples covering the whole lactation of two sows. In contrast to the ash of the colostrum of most other species, the ash of the colostrum of the sow is lower than that of normal milk, and as lactation is established there is a rise in the total ash content, and in its main constituents, calcium and phosphorus.

The aim of this study was to identify and rank the various factors, in particular those involving feeding, that affect the proportion of caseins in milk true protein. Twenty-nine feeding trials involving 821 lactations were assessed, and lactoprotein genetic variants were known for 551 of these. The main factor affecting the casein: protein ratio was the genetic variant of β-lactoglobulin: once corrected for other factors, the milk of BB type animals had a ratio nearly 30 g/kg total protein higher than AA animals. κ-Casein variant B also had a positive effect (+12 g/kg in favour of BB relative to AA animals). Except in the last weeks of pregnancy and the first weeks of lactation, the casein[ratio ]protein ratio varied little during lactation. It was significantly reduced when milk cell count exceeded 200000 cells/ml, even in the absence of clinical mastitis. It also decreased slightly with parity. Among the various dietary factors studied (level and type of nitrogen and energy supplies, forage type and preservation method), none had any significant effect on the milk casein[ratio ]protein ratio, except in drastic dietary situations. That ratio increased very slightly in parallel with the animals' milk yield and milk protein content. In practice, measuring the milk protein content in animals free from clinical mastitis remains a very precise predictor of casein content, accounting for 93% of its variation.

A turbidimetric method, based on light reflection, was used to study acid coagulation of reconstituted skim milk at low temperature. Capillary viscosimetry, gelograph and laser granulometer techniques were also employed. Acidification of milk was produced by hydrolysis of glucono-δ-lactone. The general shape of the turbidimetric signal as a function of pH or time can be divided into three stages: a lag phase followed by a significant decrease and then a final rise. Two factors have a great influence on the development of milk turbidity, pH and temperature. Dynamic viscosity measurements can be related to the turbidimetric signal while laser granulometrie measurements cannot be correlated with changes in turbidity: the micelle size distribution remains constant until the first signs of gelation. As previous work showed, dynamic viscosity diminishes with acidification until a particular pH is reached (pH 5·9 at 15°C and pH 5·75 at 20°C). We have related this latter period to the turbidimetric lag phase. As milk turbidity became lower than its initial value (pH 5·75 at 15°C and pH 5·55 at 20°C), dynamic viscosity increased significantly. The release of material from micelles (β-casein and Ca) could explain this phenomenon. In the same way, further increase of turbidity at a particular pH value (pH 5·3 at both 15 and 20°C) coulcl be partly due to the reincorporation of soluble casein monomers in the micelle framework. As the onset of gelation was approached, turbidity still increased as a result of gel network formation.

The study was carried out in a commercial flock on 286 Churra breed ewes (566 half-udders) assigned to three lots depending on the type of antibiotic dry therapy received in the lactation previous to the one studied. One-hundred-and-four ewes were given complete therapy in all udders, 103 received selective therapy of infected half-udders, and 79 received no therapy at all. Half-udders of all animals were sampled for bacteriological study at ≤72 h (lambing), 60 d, 120 d, and 155 d (drying-off) post partum. Dry therapy, parity number, lactation stage and therapy×parity interaction contributed significantly to variation in intramammary infection prevalence. Antibiotic dry therapy had the most significant effect. Prevalence during the whole of the subsequent lactation was significantly lower in lots receiving complete (18·8%) and selective (15·6%) dry therapy than in the untreated control lot (48·3%). Coagulase-negative staphylococci and streptococci (in particular Streptococcus agalactiae) were the organisms most significantly affected by dry therapy. In untreated ewes, prevalence increased noticeably from the 2nd to the 6th and subsequent lactations, but no significant changes were observed in the treated lots. Milk yield in the dry treated lots was 6·9% higher that in the untreated one. It was concluded that complete and selective treatments of ewes at drying-off were efficient and comparable methods of reducing the intramammary infection prevalence, improving bacteriological quality of milk, and increasing milk yield.

Kefir is a fermented-milk beverage originating and widely consumed in the Caucasus as well as in Eastern Europe and is a source of bacteria with potential probiotic properties. Enterohaemorrhagic Escherichia coli producing Shiga toxin is commonly associated with food-transmitted diseases; the most prevalent serotype causing epidemics is Esch. coli O157:H7. The aim of this study was to evaluate the antagonism of Lactobacillus plantarum isolated from kefir against the action on Vero cells of supernatants of the Esch. coli O157:H7 strain 69160 expressing the type-II Shiga toxin (Stx2) and to study the role of the Lactobacillus cell wall in that inhibition. Spent culture supernatants of Esch. coli O157:H7 strain 69160 led to cytotoxic effects on cultured eukaryotic cells as evidenced by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide–cleavage assay or by lactate-dehyrogenase release. Lb. plantarum CIDCA 83114 reduced the cytotoxic activity of Stx present in strain-69160 supernatants, and this protection was markedly higher than those of Lactobacillus kefir CIDCA 83113 and 8348 and Lb. delbrueckii subsp. bulgaricus CIDCA 333. This antagonism of cytotoxicity was mimicked by Lb. plantarum cell walls but was reduced after heating or protease treatments, thus indicating a protein or peptide as being involved in the protection mechanism. The cell surface of the lactobacilli bound the subunit B of Stx thereby decreasing the cytotoxicity. These interactions could constitute the first step in preventing the damage induced by Esch. coli O157:H7 supernatants, thus representing a valuable means of potentially mitigating the noxious effects of this food pathogen.

The apparent diffusion coefficients for NaCl in Romano-type cheese salted by brining or dry salting were ∼0·23 cm2/d. A plot of the natural logarithm of % salt-in moisture against distance was almost linear, the slope of which is the distance over which the salt concentration decreases by a factor of 1/e (0·368). Such plots may be useful in predicting the concentration of NaCl at any point in the cheese after any period of brining. After 9 d brining, the water to salt flux (ratio of outflow of water to inflow of NaCl) decreased from 2·42 at the surface to ∼0·5 in the middle zone of the cheese and increased again to > 1 at greater distances from the cheese/brine interface.

Staphylococci have been isolated from various sites of the body of healthy sheep, as well as from many infections of those animals, the main one being mastitis. The objective of this review is to appraise the importance and significance of staphylococci in causing mastitis in ewes. The review includes a brief classification and taxonomy of staphylococci and describes the procedures for their isolation and identification, as well as their virulence determinants and the mechanisms of resistance to antibacterial agents. Various staphylococcal species have been implicated in staphylococcal mastitis and the characteristics of isolates are discussed with regards to potential virulence factors. Staphylococcal mastitis is explicitly described, with reference to sources of infection, the course of the disease and the relevant control measures. Finally, the potential significance of staphylococci present in ewes’ milk for public health is discussed briefly.

1. The composition has been studied of the milk of forty-four sows in the course of sixty-eight lactations. The milk was obtained by machine milking following intravenous injection of oxytocin.

2. Definite lactational trends have been observed for all the major constituents, and the third week seems a critical stage for most of the milk components.

3. The mean values for the milk, based on the analyses of over 450 samples from the seventh to fifty-sixth day of the lactation were: fat 9·58 %, protein 6·11 %, lactose 4·62 %, ash 0·92%. Such figures are considered to be rather meaningless for most practical purposes, in view of the marked changes over the course of lactation.

4. The day-to-day variation in the composition of sow's milk has been studied. Whereas the fat value changes considerably, the non-fat constituents show a less marked variation. Difficulties in securing a representative sample of the weekly milk have been overcome by preparing a composite sample from three milMngs within the week.

5. Some preliminary work has been done on variation in the composition during the process of milking. Sequential samples show an erratic fat content, especially during the early part of the lactation. When calculated on a fat-free basis, the protein, lactose and ash contents are relatively constant during the process of milking.

Measurements of the zeta potential and particle size of casein micelles in skim milk suspensions at natural and lower pH have been made using the technique of electroacoustics. This technique requires no dilution or change of environment of the casein micelles. The zeta potential obtained at natural pH for a commercial skim milk suspension was −18 mV; it became less negative with decreasing pH. The median particle size observed at natural pH for a commercial skim milk suspension was 0·2 εm, in good agreement with previously reported values. The particle size increased as the pH was decreased.