The physicochemical characteristics and the renneting properties of milks from Lacaune ewes are reported. The ewes belonged to divergent genetic lines termed ‘low’ or ‘high’ and were selected on a combination of fat and protein yield. The 179 second to fifth parity ewes were sampled three times during lactation at about 50, 135 and 175 d in milk. Physicochemical and renneting variables were principally influenced by days in milk and somatic cell count, whereas β-lactoglobulin genotype, parity and divergent lines had relatively few effects. Fat and protein content increased throughout lactation, whereas rennet gel firming rate decreased. Salt distribution and micellar characteristics were also significantly affected by days in milk. Milks with high somatic cell count were characterized by high values of pH and soluble nitrogen content and rennet coagulation properties were significantly affected at >3×105−5×105 cells/ml milk. Divergent lines had a strong effect on milk yield, but no effect on milk composition consistent with the selection criteria. Gel firming rate was slightly higher in milks from high yield ewes. Protein content, Ca concentration, pH and micelle characteristics were the main factors related to variations in the renneting properties of the milks.

Considerable inhibitory antibacterial actions were exerted by the soybean 11S subunit comparable with nisin on the proliferation of total viable count, Pseudomonas count and Enterobacteriaceae count in bovine milk stored at 4 or 25 °C for 30 d and 48 h, while 7S and lysozyme were much less effective. The maximum magnitudes of bacterial reduction by 11S and nisin were in the range 2–4 log CFU/ml. The proliferation of 3 pathogenic bacteria (Listeria monocytogenes, Salmonella Enteritidis and Escherichia coli O157:H7) artificially inoculated into raw milk stored at 4 or 25 °C were particularly and significantly (P<0·05) reduced by 11S subunit and nisin (0·5% w/v), but only slightly by 7S and moderately by lysozyme. Lactose consumption, acidity development and casein degradation during storage of bovine raw milk were attenuated during storage at 4 or 25 °C and sensorial traits were better maintained by supplementation with 11S (0·5% w/v). 11S subunit may be used a safely food preservative, if permitted.

Inhibition of milk ejection in cows by oxytocin receptor blockade (Atosiban) and α-adrenergic receptor stimulation (phenylephrine) prior to prestimulation was compared with inhibition of milk ejection in unfamiliar surroundings. In addition, Atosiban and phenylephrine were administered after a 1 min prestimulation or 1 min after the start of milking. Oxytocin concentrations increased during milking in all treatments. The spontaneously removed milk fraction (before oxytocin was injected) was similar for Atosiban and phenylephrine treatments and in unfamiliar surroundings, but lower than in controls. Peak flow rates were similar in all treatments, but reduced as compared with controls when phenylephrine and Atosiban were administered before prestimulation. Peripheral (Atosiban, phenylephrine) and central (unfamiliar surroundings) inhibition of milk ejection reduced the amount of available milk similarly. Drug treatments resulted in similar peak flow rates; however, teats were contracted after phenylephrine administration but not after Atosiban. The inhibition induced by Atosiban could be abolished by oxytocin injection, but not that induced by phenylephrine, which was antagonized by α-adrenergic receptor blockade. These results indicate that inhibition of milk ejection through activation of α-adrenergic receptors is based on blockade of milk flow into the cistern, but not through the teats.

Changes in heat stability and Ca2+ activity of recombined concentrated milk (18% solids non-fat:8% fat) induced by the additions of 0·011–0·217 mol phosphate/kg skim milk solids (SMS), 0·022–0·217 mol citrate/kg SMS, 0·011–0·022 mol Ca/kg SMS and 0·016–0·067 mol EDTA/kg SMS were evaluated. Heat stability was assessed using an objective method which involved determination of viscosity after heating under controlled conditions. Low levels of added phosphate and citrate generally effected an acid shift of the viscosity–pH profile, while higher levels caused a broadening of the profile. Addition of CaCl2 at a level of 0·011 mol/kg SMS resulted in a narrowing of the viscosity–pH curve; additions of higher levels resulted in a non-heat stable recombined milk concentrate. EDTA also caused a narrowing of the viscosity–pH curve. The results highlight the importance of pH control for effective stabilization of recombined milk concentrates by additions of phosphate and citrate.

Sow milk protects the piglet against infectious diseases through a variety of mechanisms. In this study, the presence of potentially probiotic lactic acid bacteria in this biological fluid was investigated. Milk samples were obtained from 8 sows and a total of 19 rod-shaped isolates were selected for identification and assessment of their probiotic potential. RAPD profiling revealed the existence of 8 different genetic profiles among them. One representative of each profile was selected for further characterization and they were identified as Lactobacillus reuteri, Lb. salivarius, Lb. plantarum, Lb. paraplantarum, Lb. brevis and Weissella paramesenteroides. Then, their probiotic potential was evaluated through different assays, including survival in conditions simulating those existing in the gastrointestinal tract, production of antimicrobial compounds, adherence to intestinal mucin, production of biogenic amines, degradation of mucin, and pattern of antibiotic sensitivity. Three strains, Lb. reuteri CR20 (a reuterin-producing strain), Lb. salivarius CELA2 (a bacteriocin-producing strain) and Lb. paraplantarum CLB7 displayed the highest probiotic potential.

Bacterial post pasteurization contamination with psychrotrophic Gram-negative rods (GNR) was measured in commercial milks before and after transfer to retail containers. The tanks of pasteurized milk feeding the filling units contaminated milk less often (39% of samples) but usually at a higher level than the filling units (92% of samples). The number of GNR present had a considerable influence on the shelf life of milk, and the range found in commercially pasteurized milk was reflected in a wide range of shelf lives.

Possible mechanisms for the production of volatile sulphur compounds during the ripening of Cheddar cheese have been studied. Slurries of cheese made with and without starter organisms were treated with dithiothreitol (DTT) and the chemical composition of the headspace examined. Cheeses were also pressed from curd treated with DTT and glutathione (GSH). Reactions occurring between methionine, cystine and Na caseinate and reducing agents cysteine, DTT and GSH were also studied. In addition, the reactions of H2S with methionine and Na casein. ate were investigated.

Treatment of cheeses with DTT and GSH resulted in the production of H2S and methanethiol (CH3SH) together with the development of Cheddar flavour. Similar treatment of methionine and Na caseinate also yielded H2S and CH3SH whereas Cystine produced only H2S. H2S reacted with both Na caseinate and methionine to yield CH3SH.

These results are consistent with the occurrence of some of the chemical reactions studied during the ripening of Cheddar cheese.

This work describes the effect of the hydrolysis time and pressure (0·1–400 MPa) on the proteolysis of β-lactoglobulin A (β-lg A) with trypsin, either conducting hydrolysis of β-lg under pressure or hydrolysing β-lg that was previously pressure treated. Pressurisation, before or during enzyme treatments, enhanced tryptic hydrolysis of β-lg. Trypsin degraded pressure-modified β-lg and pressure-induced β-lg aggregates, favouring proteolysis to the intermediate degradation products: (Val15-Arg40), (Val41-Lys69)S-S(Leu149-Ile162) and (Val41-Lys70)S-S(Leu149-Ile162). These were further cleaved at the later stages of proteolysis to yield: (Val15-Tyr20), (Ser21-Arg40), (Val41-Tyr60), (Trp61-Lys69)S-S(Leu149-Ile162) and (Trp61-Lys70)S-S(Leu149-Ile162). Particularly, in the tryptic hydrolysates of pre-pressurized β-lg, two other fragments linked by disulphide bonds: (Lys101-Arg124)S-S(Leu149-Ile162) and (Tyr102-Arg124)S-S(Leu149-Ile162), were found. These corresponded to rearrangement products induced by SH/SS exchange between the free thiol group of Cys121 and Cys160, that normally forms the disulphide bond Cys66-Cys160. In the light of these results, structural modifications of β-lg under high pressure are discussed.

Effects of systematic environmental factors and milk production and quality traits on milk coagulation properties (MCP), and on repeatability of those traits were estimated from 979 milk samples collected once a month over a period of 2 years from 83 Finnish Ayrshire cows. Estimation was based on a multitrait animal model and REML methodology. In addition, persistence of non-coagulation of milk in individual cows, and factors associated with it were established from a sub sample of 24 cows producing non-coagulating (NC) milk at least once. MCP were at their best during the first lactation, at the beginning and at the end of lactation, and during grazing seasons. Variation in MCP with systematic environmental factors was partly due to variation in composition and quality of milk, especially in pH and ln (somatic cell count, SCC). Coefficients of repeatability for milk coagulation time and curd firmness were 0·65 and 0·68. These estimates were of the same magnitude as those for protein content, but were higher than those for daily milk yield, fat content, pH, and SCC. Based on the repeatability estimates for the milk coagulation traits and effects of the environmental factors, cows should be sampled at least three times during a lactation to estimate reliably breeding values for the milk coagulation traits. A total of 10% of the milk samples did not coagulate in 30 min after addition of rennet. Cows that produced NC milk at least once (30% of the cows) could be classified into those that produced NC milk only a few times during a lactation and those that produced NC milk at almost every sampling. Based on logistic regression analyses, peak and mid-lactation, high milk yield, low protein and fat content and high pH increased the risk of non-coagulation of milk.

A total of 116 molecular species of triglycerides were identified in milk fat, using a combination of HPLC and GLC. Triglyceride composition was predicted from the random composition, which was calculated on the basis of the mole fractions of the main fatty acids making up the total triglyceride fraction. The qualitative composition of the milk fat was similar in cows', ewes' and goats' milk. In all three milks the partition number of the main triglycerides was 46, but the proportions of the triglycerides with partition numbers of 34, 38, 42, and 48 exhibited substantial differences among the milks of the three species.

The aim of the study was to describe the characteristics of cleaning procedures for milking equipment applied in intensive dairy farms in Lombardy (Italy) and to study their relationships with bacterial count of bulk milk and hygienic condition of milking machine components. A group of 22 dairy farms was visited twice (winter and summer) in order to collect bulk tank milk and post-rinse water samples and swabs from liners and milk receiver. Samples were analysed to determine: standard plate count (SPC), laboratory pasteurization count (LPC), psychrotrophic bacteria count (PBC), coliform count (CC) and Escherichia coli. Cleaning procedures were monitored using electronic milk flow meters with specific software for the measurement of the duration of each cleaning phase, circulating solution temperature and electrical conductivity, turbulence and water filling percentage of pipelines. The results showed that farms classified as high and low milk total bacteria count significantly differed both in terms of liners and receiver bacterial contamination and in terms of water temperature reached during the detergent phase of cleaning milking equipment. Significant positive correlations were found among total bacteria count in milk and bacterial contamination of the liners. Maximum water temperature reached during the cleaning cycle of milking equipment was very low (34·4±8·9°C on average); most of the observations (88·6%) corresponded to water temperatures <45°C. Cleaning temperature was related to psychrotrophic bacteria count of milk and post-rinse water and coliform count in liners. Routine check and regulation of water temperature during the washing phase of the milking machine can be a simple and effective way to control one of the main risk factors for bacteriological quality of bulk tank milk.

We studied the mammary immune response to different mammary pathogenic Escherichia coli (MPEC) strains in cows, hypothesising that the dynamics of response would differ. E. coli is a major aetiologic agent of acute clinical bovine mastitis of various degrees of severity with specific strains being associated with persistent infections. We compared challenge with three distinct pathogenic MPEC strains (VL2874, VL2732 and P4), isolated from different forms of mastitis (per-acute, persistent and acute, respectively). A secondary objective was to verify the lack of mammary pathogenicity of an environmental isolate (K71) that is used for comparison against MPEC in genomic and phenotypic studies. Twelve cows were challenged by intra-mammary infusion with one of the strains. Cellular and chemokine responses and bacterial culture follow-up were performed for 35 d. All cows challenged by any of the MPEC strains developed clinical mastitis. Differences were found in the intensity and duration of response, in somatic cell count, secreted cytokines (TNF-α, IL-6 and IL-17) and levels of milk leucocyte membrane Toll-like receptor 4 (TLR4). A sharp decrease of TLR4 on leucocytes was observed concomitantly to peak bacterial counts in milk. Intra-mammary infusion of strain K71 did not elicit inflammation and bacteria were not recovered from milk. Results suggest some differences in the mammary immune response to distinct MPEC strains that could be correlated to their previously observed pathogenic traits. This is also the first report of an E. coli strain that is non-pathogenic to the bovine mammary gland.

The ability of Listeria monocytogenes to grow at low temperatures and increase to hazardous levels during storage of dairy products is of great concern to the dairy industry. List. monocytogenes was detected in 3·6% of 774 cows' milk samples from 114 farms in Central Spain (Gaya et al. 1998). Ewes' and goats' milks produced in Spain had contamination levels of 2·2 and 2·6% respectively (Rodríguez et al. 1994; Gaya et al. 1996). List. monocytogenes may survive during the manufacture and ripening of most cheese varieties, with higher risk in soft surface-ripened cheeses owing to the rise in pH during ripening (Maisnier-Patin et al. 1992; Giraffa & Carminati, 1997).

The efficacy with which actively growing bacteriocin-producing cultures inhibit List. monocytogenes in some cheese varieties has been demonstrated. Nisin-producing starters inhibited List. monocytogenes V7 in Camembert cheese (Maisnier-Patin et al. 1992) and List. innocua BL86/26 in raw ewes' milk Manchego cheese (Rodríguez et al. 1998). A lacticin 3147-producing starter culture (McAuliffe et al. 1999) reduced List. monocytogenes Scott A levels in cottage cheese. Inoculation of milk with enterocin AS-48-producing Enterococcus faecalis INIA 4 inhibited List. monocytogenes strains Ohio and Scott A during the manufacture and ripening of Manchego cheese (Nuñez et al. 1997).

Semi-hard cheese varieties from raw or pasteurized cows' milk mixed with different proportions of ewes' and/or goats' milk represent ∼ 50% of Spanish cheese production. The objective of the present work was to evaluate the antilisterial activity of three bacteriocin-producing lactic acid bacteria strains isolated from milk (Rodríguez et al. 2000) during the manufacture and ripening of a semi-hard cheese manufactured from raw milk.

Polymorphism of caprine milk proteins was studied by capillary electrophoresis. Identification of casein (CN) fractions was effected by using isolated fractions from cation-exchange fast protein liquid chromatography. Genetic polymorphisms in caprine αs2-CN, αs1-CN, β-CN and κ-CN have been determined. κ-CN A and B, β-CN A and null, αs2-CN A, B and C, αs1-CN A, B, C and null, and other forms with intermediate and low αs1-CN content have been identified. The capillary electrophoresis method made it possible to analyse whole caprine milk using simple sample preparation and was rapid, automated and suitable for phenotyping studies. This method may also permit the quantitative study of different protein fractions.

The internal arrangement of the mammary gland cavity system, cisternal and alveolar milk fractions and the characteristics of milk ejection were investigated in buffaloes. Twenty-four Murrah buffaloes in three different stages of lactation and of two age groups were used. Continuous ultrasound cross-sections during milk ejection induced by exogenous oxytocin were performed to record the latency period of milk ejection. Buffaloes had small cisterns and the cavity area in the teat and gland regions were not significantly different (P>0·05). The animals had long teat canals (3·1±0·1 cm), longer in the hind than fore quarters. Cisternal milk yield was low (0·17±0·01 kg) and cisternal fraction was only 4·9±0·1% of the total milk. The cisternal area (cm2) was 69·6±4·6, 51·61±4·8 and 26·01±4·8 while the cisternal yield (kg) was 0·32±0·05, 0·18±0·05 and 0·05±0·05 in early, mid and late lactation, respectively. A close correlation (r=0·87, P<0·05) existed between the ultrasound cisternal area and cisternal milk yield. The latency period of induced milk ejection was similar to that reported for cows (25±1 s) and was negatively correlated with milk yield (r=−0·75, P<0·05). Milk ejection occurred shortly after elevated oxytocin concentrations were present. Delayed milk ejection reported earlier in this species must therefore be due to the absence of cisternal milk and delayed oxytocin release. An increase in teat length and circumference at milk ejection was also evident in the ultrasound cross sections.

Machine milking induced repeatable, short-term changes in thickness of the teat apex. These changes were measured with a spring-loaded caliper instrument under milking conditions that imposed differing forces on the teat apex. The mean percentage changes in teat end thickness (relative to the premilking values for individual teats) varied from 10% decrease up to 20% or more increase depending on the particular milking system used. The overall decrease in teat end thickness associated with cannula milking, milking at very low vacuum levels or milking with positive pressure pulsation may result from: (i) decrease in the intramammary pressure; and/or (ii) small changes in tone of teat musculature; and/or (iii) changes in the distribution of interstitial fluids in the teat apex. The overall increase in teat thickness caused by conventional or PKME milking systems results mainly from oedema (the extravascular accumulation of fluid). It is likely that milking equipment can, and should, be designed to minimize circulatory impairment resulting in oedema of the teat.

A tributyrin esterase was purified from Lactococcus lactis subsp. cremoris E8 using FPLC chromatography. This was the major esterase activity observed in strain E8 and was associated with a single protein with a subunit molecular mass of 29 kDa and a holoenzyme of molecular mass 109 kDa. The enzyme was active against tributyrin and p-nitrophenyl butyrate. The N-terminal sequence of the enzyme was determined. The enzyme had a pH optimum in the neutral range, was stable on freezing at −20 °C, and had a half life of 1 h at 50 °C.

Machine-induced changes in teat thickness were measured in a randomly selected group of 22 cows from a commercial dairy herd consisting of 110 cows during an experiment lasting 1 year. Half the cows used were free from mastitis whereas the remainder had at least one quarter infected by environmental pathogens. Teats were classified according to a threshold change in teat end thickness of 5%. The relationships between quarter infection or teat duct colonization and teat end thickness changes induced by machine milking were investigated. Teats with > 5% change in thickness had significantly increased teat duct colonization and a slight, non-significant, increase in quarter infection. We conclude that machine-induced changes in teat end thickness are predisposing factors for teat duct colonization by environmental pathogens. This may provid: an increased new infection risk, especially when hygiene is poor.

The changes in milk fat globules and fat globule surface proteins of both low-preheated and high-preheated concentrated milks, which were homogenized at low or high pressure, were examined. The average fat globule size decreased with increasing homogenization pressure. The total surface protein (mg m−2) of concentrated milk increased after homogenization, the extent of the increase being dependent on the temperature and the pressure of homogenization, as well as on the preheat treatment. The concentrates obtained from high-preheated milks had higher surface protein concentration than the concentrates obtained from low-preheated milks after homogenization. Concentrated milks heat treated at 79°C either before or after homogenization had greater amounts of fat globule surface protein than concentrated milks heat treated at 50 or 65°C. This was attributed to the association of whey protein with the native MFGM (milk fat globule membrane) proteins and the adsorbed skim milk proteins. Also, at the same homogenization temperature and pressure, the amount of whey protein on the fat globule surface of the concentrated milk that was heated after homogenization was greater than that of the concentrated milk that was heated before homogenization. The amounts of the major native MFGM proteins did not change during homogenization, indicating that the skim milk proteins did not displace the native MFGM proteins but adsorbed on to the newly formed surface.