A kinetic model was proposed for describing the curd assembly of skimmed goats' milk during enzymic coagulation. The enzymic coagulation of milk was monitored using an optical sensor that measured diffuse reflectance (light backscatter) at 880 nm. The appearance of a shoulder, at low temperatures and protein concentrations, in the diffuse reflectance ratio profile after the inflection point of the curve (Tmax) appeared to separate the aggregation and curd firming steps. The diffuse reflectance ratio profile after Tmax was attributed to the overlapping of casein micelles aggregation and curd firming reactions. The developed kinetic model combined a second order reaction model to describe aggregation reactions and a first order reaction model to describe firming processes reactions. A completely randomised block design with three replications was used to determine the effect of protein concentration and temperature on kinetic constants. Milk was adjusted to three levels of protein (30, 50 and 70 g/kg), and coagulated at five temperatures (20, 25, 30, 35 and 40°C) to test a wide range of processing conditions. Data points from each profile after Tmax were fitted to the proposed model using non-linear regression. The average R2 and standard error of prediction (SEP) for 45 tests conducted were in the range of 0·9975±0·0027 and 0·0081±0·0037, respectively. A significant increase in characteristic times for aggregation (τ2) and curd firming processes (τ1) were found when temperature decreased or protein increased. Theoretical asymptotic value of reflectance ratio, R∞, increased with increasing level of protein and temperature (P<0·05). The parameter β1, which represented the fraction of diffuse reflectance ratio attributed to aggregation, decreased with increasing temperature and decreasing protein.

In the context of identifying intrinsic time temperature integrators (TTIs) for evaluating thermal processing of milk, the possible influence of seasonal variation in milk composition on the applicability of alkaline phosphatase (ALP), hydroxymethylfurfural (HMF), lactulose and furosine for process impact assessment was studied. Hereto inactivation and formation kinetics of these indicators were analysed in milk samples collected over a one year period. Based on previous research (isothermal and non-isothermal heating conditions) it was assumed that thermal inactivation of ALP followed first order kinetics, and formation of HMF, lactulose and furosine could be described by pseudo-zero order kinetics. This allowed the use of a simplified experimental design to obtain the kinetic parameters. Based on 90% joint confidence regions, kinetic parameter values differed significantly between different batches of milk for all four indicators. Additionally, variable ALP activities and HMF concentrations were observed in the raw milk samples. Nevertheless, the observed differences did not seem to restrict the applicability of the selected TTIs as illustrated by the construction of temperature time tolerance (TTT-) diagrams. Through these diagrams, use of the TTIs implied an uncertainty of approximately 2°C between equivalent processes.

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.

For practical purposes the casein content of milk is often estimated from the crude protein content using a general conversion factor. This is done even though it is known that several factors can influence the percentage of casein nitrogen in the total nitrogen (casein number). The uncontrolled variation in casein number affects optimization of cheese production because casein is a limiting factor for cheese yield. Fourier transform infrared spectrometry has recently been introduced for casein determination. Using this technique we obtained a standard error of prediction (SEP) of 0·033% for casein concentrations in the range 2·1–4·0%. The true prediction error was estimated as 0·025%. The correlation between casein numbers obtained by reference analysis and infrared spectrometry could be expressed by an R2 of 0·73 and an SEP of 0·89 for casein numbers in the range 70·7–81·0.

Release of oxytocin (OT) is essential for milk ejection in dairy cows (Lefcourt & Akers, 1983; Bruckmaier & Blum, 1998). During milk ejection, alveolar milk is shifted into the cistern, which causes an increase of intracisternal pressure (Bruckmaier et al. 1994). To initiate maximum milk ejection at the start of milking, increasing OT concentration beyond a threshold level is sufficient (Schams et al. 1983). Increasing OT concentration beyond this threshold has no additional effect on intracisternal pressure, i.e., milk ejection (Bruckmaier et al. 1994). Stimulatory effects of milking by hand or by machine or by suckling are well documented (Gorewit et al. 1992; Bar-Peled et al. 1995; Tancin et al. 1995; Bruckmaier & Blum, 1996). At the start of milking, stimulatory effects of machine milking without pre-stimulation or with a manual pre-stimulation and subsequent machine milking cause the release of comparable amounts of OT (Gorewit & Gassman, 1985; Mayer et al. 1985; Bruckmaier & Blum, 1996), whereas the timing of the applied pre-stimulation is important for the shape of the milk flow curve. Should the pre-stimulation period be too short, or absent altogether, the start of the main milk flow is delayed resulting in a bimodal milk flow profile (Bruckmaier & Blum, 1996). Furthermore, the stimulation of only one teat causes an OT release similar to that caused by stimulation of all four teats (Bruckmaier et al. 2001). However, milk production is greater for hand milking or suckling than for machine milking, possibly owing to higher OT concentrations (Gorewit et al. 1992; Bar-Peled et al. 1995).

Sedimentation Field Flow Fractionation (SdFFF) was combined with Photon Correlation Spectroscopy (PCS), to characterize changes in the structure of the colloidal particles of reconstituted skim milk of diameter >50 nm (aggregates of casein and calcium phosphate known as casein micelles) with the changes in partitioning (with the addition of salt) of calcium (Ca), inorganic phosphate (Pi) and casein between the serum and colloidal phases of the milk. The number weighted particle size distributions are determined. These are well represented by a log-normal distribution. Methods are presented for estimating the relative contributions of scattering and absorbance to the SdFFF detector signal and for taking both into account when analysing SdFFF data. The values found for the effective density of the casein micelles were in good agreement with the literature and ranged from (1·06–1·08 g cm−3) according to the composition of micelles. The changes in the scattering intensity as determined by PCS correlated with the changes in the particle composition. Although the concentrations of colloidal calcium phosphate (CCP) (1·1–3·5 g/kg milk) and micellar casein (18·1–27·2 g/kg milk) varied considerably only small changes in the size distribution of particles >50 nm diameter were observed except for milk to which 30 mmol Pi+10 mmol Ca/kg milk had been added where the particle size distribution shows a swelling of the particles consistent with a lower than expected value for the particle density. These observations suggest that the micelles have the ability to both lose (depleted micelles) and accommodate (enriched micelles) more casein, calcium and inorganic phosphate in their interior, thus confirming the model of the micelles which postulates an open structure allowing freedom of movement of casein and small ions.

The effects of activation of the lactoperoxidase (LPO) system by H2O2–NaSCN and hydrogen peroxide (H2O2) on the accessibility of sulphydryl groups (SH) in skimmed milk, and on the dynamic rheological properties of the resulting yoghurt were investigated. Four different concentrations of each reagent (20–80 mg H2O2–NaSCN/kg milk and 100–400 mg H2O2/kg milk) were compared. Clear negative correlations were noted between the accessibility of SH groups and both LPO activation rate and H2O2 concentration. Also the native PAGE pattern of the heat-treated samples showed that with increase in the H2O2–NaSCN and H2O2 concentrations, the level of interaction between β-lactoglobulin (β-lg) and κ-casein (κ-CN) decreased. The complex modulus (G*) of skimmed milk yoghurts declined gradually with the decrease in the concentration of accessible SH groups accordingly. Tan δ values of yoghurt samples were found to be different from the control, but close to each other, indicating that protein interaction forces taking place in the formation of gel networks of treated yoghurts were different from the control.

Yeast extract was used as a nutrient for growing lactobacilli in reduced-fat Cheddar cheese as early growth of non-starter lactic acid bacteria (NSLAB) in Cheddar cheese is suppressed by pasteurization of milk and the hostile environment of the cheese. Reduced-fat Cheddar cheese was manufactured from 100 kg standardized milk on two occasions. After milling, the curd was divided into two portions, C and E. To control portion, C, salt was added at normal levels. A mixture of salt and yeast extract was added to the experimental, E. The cheeses were ripened for 7 months at 8 °C and assessed for proteolysis and NSLAB growth during ripening. Mean % moisture, fat, protein, salt and pH were 40·6, 20·5, 31·1, 1·72 and 5·22 respectively, in E cheeses, and 39·5, 20·5, 30·9, 1·68 and 5·22, respectively, in C cheese. NSLAB counts in E cheeses were 101, 103, 105 cfu/g compared with 0, 101, 104 cfu/g in C respectively, after 1, 7 and 30 d of ripening. After 60 d, cell densities of NSLAB were similar (∼106 cfu/g) in C and E cheese. Addition of yeast extract to curd affected neither the electrophoretic patterns of cheese nor its water-soluble N content during ripening. However, the total free amino acids were significantly higher in E cheese than C cheese throughout ripening, suggesting faster secondary proteolysis in the former cheeses. A 6-member trained descriptive panel evaluated the cheese at 7 months and found that the E cheeses had higher intensities of whey, fruity, sulphur, nutty, sweet and sour flavours, but had lower intensities of brothy flavours as compared to C cheeses. Also, the E cheeses were perceived to be more mature than corresponding C cheese. Results show that addition of yeast extract to cheese curd is a promising method of enhancing flavour development in ripened cheeses.

Human plasminogen undergoes a large tertiary structural change in the presence of lysine derivatives (e.g. ε-amino caproic acid, EACA). This change facilitates human plasminogen activation by human plasminogen activators, resulting in elevated blood plasmin levels. It is hypothesized that this structure-function relationship is similar for bovine plasminogen. The objectives of this study were to investigate the effect of the ligand EACA on the secondary structure of plasminogen (bovine, human, and rabbit) and the tertiary structure of bovine plasminogen using Fourier-transform infrared spectroscopy (FTIR). Spectra of plasminogen, EACA, and a mixture of plasminogen and EACA in water and deuterium were collected using FTIR. Fourier-self deconvoluted spectra in the amide I region (1700–1600 cm−1) were used to detect changes in secondary structure of plasminogen after EACA addition. Change in bovine plasminogen tertiary structure was determined by comparing ratios of amide II (1600–1500 cm−1) to amide I bond intensities over time for samples in deuterium. No differences in secondary structure were observed for any plasminogen in the presence of EACA; however, addition of EACA significantly changed tertiary structure of bovine plasminogen. This tertiary structural change indicates a transition from a folded to an unfolded state, which could be more easily converted to plasmin. These results are consistent with reported human plasminogen studies using neutron scattering (tertiary structure) and circular dichroism (secondary structure) methods.

In dry cow therapy (DCT), antibiotics are usually injected direct into the mammary gland after the last milking of the lactation. Most products are designed to eliminate existing intramammary infections (IMI) caused by Staphylococcus aureus and Streptococcus agalactiae and to prevent the establishment of new IMI caused by major pathogens during the early non-lactating period (Nickerson et al. 1999). Systemic therapy has been attempted as a way of improving the cure rates of intramammary treatments of clinical and subclinical mastitis during lactation (Ziv, 1980a; Calvinho et al. 1988; Owens et al. 1988). For systemic therapy to be useful, effective passage of the drug from blood to the foci of infection must be achieved. Maintaining an effective antibacterial concentration in the udder depends on the physicochemical properties of the drug, the dose, the bioavailability of the injected formulation, and the sensitivity of the pathogen (Ziv et al. 1980a, b). The theoretical pharmacokinetic and pharmacodynamic basis for systemic DCT has been reported (Soback, 1988). When used in an attempt to improve cure rates of IMI, subcutaneous injection of tilmicosin at drying-off was ineffective against Staph. aureus IMI (Nickerson et al. 1999) and intramuscular (i.m.) oxytetracycline, in combination with intramammary cephapirin dry-cow treatment did not improve the cure rate for Staph. aureus mastitis (Soback et al. 1990a; Erskine et al. 1994). Nevertheless, i.m. tylosin treatment 2 weeks before the expected day of calving decreased IMI after calving (Zecconi et al. 1999) and subcutaneous norfloxacin nicotinate applied at the cessation of milking proved useful in controlling Staph. aureus infections (Soback et al. 1990a). Moreover, the incidence of this pathogen after systemic DCT may be significantly lower compared with untreated control groups (Soback et al. 1990a, b).

Alpha-lactalbumin (α-la), a calcium metalloprotein, is one of the major serum-proteins in ruminant milk (Jenness, 1982) and induces lactose synthesis in the mammary gland by interacting with the enzyme UDP-galactosyltransferase, giving rise to the heterodimer enzyme lactose synthase (Ebner & Brodbeck, 1968; Kuhn, 1983). The goat α-la transcription unit (LALBA), located on chromosome 5 (Hayes et al. 1993), is organized in 4 exons varying in length from 75 nucleotides (3rd exon) to 329 nucleotides (4th exon) coding for a 123-amino acid polypeptide chain (Vilotte et al. 1991). According to the strong similarity between bovine α-la (Vilotte et al. 1987) and human lysozyme (similar molecular weight, the same number of S-S bonds, identical N and C terminal residues; Peters et al. 1989), it has been proposed that both genes arose from a common ancestor (Vilotte et al. 1991).

Cell viability, autolysis and lipolysis were studied in Cheddar cheese made using Lactococcus lactis subsp. cremoris AM2 or Lactococcus lactis subsp. cremoris HP. Cheddar cheese was made in triplicate over a 3 month period and ripened for 238 days at 8 °C. Cell viability in cheese was lower for AM2 (a non-bitter strain) than for strain HP (a bitter strain). Autolysis, monitored by the level of the intracellular marker enzyme, lactate dehydrogenase (EC 1.1.1.27) in cheese ‘juice’ extracted by hydraulic pressure, was much greater in the cheese made using AM2 than that made with HP. Lipolysis was determined by the increase during ripening of individual free fatty acids (FFA) from butyric (C4[ratio ]0) to linolenic acid (C18[ratio ]3) measured using a high performance liquid chromatographic technique. Levels of individual FFA from butyric (C4[ratio ]0) to linolenic (C18[ratio ]3) acids increased significantly (P<0·05) during ripening in cheeses made with either starter culture. Palmitic (C16[ratio ]0) and oleic (C18[ratio ]1) acids were the most abundant FFA throughout ripening in all cheeses. Levels of caprylic (C8[ratio ]0), myristic (C14[ratio ]0), palmitic (C16[ratio ]0) and stearic (C18[ratio ]0) acids were significantly higher (P<0·05) in cheeses manufactured with Lc. lactis subsp. cremoris AM2 than in cheeses manufactured with Lc. lactis subsp. cremoris HP. Differences in levels of lipolysis between strains was not due to differences in the specific lipolytic or esterolytic activities in cell free extracts of the strains as measured by activity on triolein (lipase) and p-nitrophenylbutyrate (esterase) substrates. Therefore, evidence is provided for a relationship between the extent of starter cell autolysis and the level of lipolysis during Cheddar cheese ripening.

A fruity flavour note is traditionally regarded as a defect in cheese varieties such as Cheddar (Bills et al. 1965; McGugan et al. 1975; Horwood et al. 1987). However, fruitiness is an attribute of other cheese varieties such as Parmesan and Parmigiano Reggiano (Dumont et al. 1974; Meinhart & Schreier, 1986). It is well accepted that esters such as ethyl butanoate and ethyl hexanoate cause the fruity flavour described as apple-like or pineapple-like in raw milk and cheeses (Bills et al. 1965; Engels et al. 1997; Friedrich & Acree, 1998). The development of fruity flavour is often attributed to the esterification of free fatty acids and ethanol by esterases from lactic acid bacteria and psychrotrophic pseudomonads (Hosono et al. 1974; Morgan, 1976).

On-farm refrigeration of milk reduces the growth rate of mesophilic bacteria so allowing longer storage time of raw milk before processing. However, refrigeration creates a selective pressure favouring the multiplication of psychrotrophic bacteria present as normal contaminants in raw milk. Psychrotrophs are killed by most of the currently employed pasteurization and sterilization treatments of milk but they can produce extracellular heat-stable proteinases and lipases, which are capable of degrading various milk components, affecting the storage-life of heat-processed milk and the quality of dairy products (Champagne et al. 1994; Shah, 1994).

Caseins (αs1, β, αs2, e κ) represent about 80% of the whole protein content of ruminant milk. Each of these proteins is encoded by single copy genes (CSN1S1, CSN2, CSN1S2 and CSN3, respectively) clustered on a ∼200-kb segment of chromosome 6 (Ferretti et al. 1990; Gallagher et al. 1994) in the order: CSN1S1, CSN2, CSN1S2 and CSN3 (Mercier & Vilotte, 1993). Furthermore, in cattle and goat CSN1S1 and CSN2 are convergently transcribed (Leroux & Martin, 1996; Rijnkles et al. 1997) and are only 20 and 12 kb apart, respectively.

Lysozyme, a low-molecular weight basic protein, is an important component of the antibacterial system in milk. Lysozyme activity is higher in buffalo milk (60±3·9×10−3 units/ml) than in bovine milk (29·1±1·5×10−3 units/ml). Buffalo colostrum contains five-times more lysozyme activity than mature milk (Priyadarshini & Kansal, 2002a). Lysozyme activity in buffalo milk is not influenced by the parity of animal or stage of lactation, but it increases during extreme weather (winter and summer). Lysozyme in buffalo milk is more stable than in cow milk during storage and heat treatment. A sharp increase in milk lysozyme has been observed in buffaloes with sub-clinical mastitis (Priyadarshini & Kansal, 2002a).

Milk is a heterogeneous fluid in which the colloidal phase is homogeneously dispersed in the aqueous phase. Calcium is partitioned between the colloidal and aqueous phases and is in complex electrochemical equilibrium with several major milk components. In human and bovine milk, calcium is mainly distributed between the aqueous and casein micelle in the colloidal phases (Holt & Jenness, 1984; Neville et al. 1994). Caseins form a complex micelle structure that contains approximately 25000 phosphorylated monomers that react with calcium phosphate complexes in the milk to bind 20–40 mole calcium per mole casein (Holt & Jenness, 1984; Neville et al. 1994). Thus, the distribution of calcium between the colloidal and aqueous phases appears to be governed by the level of casein in the milk (Holt & Jenness, 1984; Neville et al. 1994). In human milk, the casein level is low; ∼25% of calcium is associated with casein, whereas in cows and goats the corresponding figure is higher at ∼65%. In rats, casein levels are among the highest in mammals and 95% of calcium is associated with casein (Neville et al. 1994). In the aqueous phase, calcium is divided among ionic calcium (Ca2+), calcium citrate and calcium phosphate. Calcium citrate and calcium phosphate constitute most of the aqueous calcium in bovine milk in contrast to less than 50% in human milk (Holt & Jenness, 1984; Neville et al. 1994). As the concentration of Ca2+ in milk appears to be essential in preserving the integrity of the mammary tight junctions during lactation (Neville & Peaker, 1981), it is important to follow its concentration precisely in mammary secretions in different stages of the reproduction cycle.

The major milk fraction stored in the bovine udder, the alveolar milk, is not available for milk removal before being actively shifted to the cisternal cavities by the milk ejection reflex (Knight et al. 1994; Pfeilsticker et al. 1996). Tactile teat stimulation, provided by the liner throughout milking, causes continuous release of oxytocin from the neuro-pituitary into the blood circulation, which induces myoepithelial contraction and shifting of alveolar milk into the cistern until the end of milking (Bruckmaier et al. 1994; Crowley & Armstrong, 1992; Gorewit et al. 1983; Lefcourt & Akers, 1983). However, milk ejection during machine milking is not complete. A residual milk fraction of 10–30% remains in the udder and is only removed after administration of supraphysiological amounts of oxytocin, usually at least 10 i.u. of oxytocin injected i.v. (Bruckmaier & Blum, 1998). In dairy practice, exogenous oxytocin is often used at high dosages to treat disturbed or incomplete milk ejection. It is reported by farmers and veterinarians that after long-term use of exogenous oxytocin animals become addicted to the treatment and withdrawal of oxytocin causes reduced milk ejection.

Dr Frank Dodd, formerly of the National Institute for Research in Dairying (NIRD) at Shinfield, Reading, has died aged 78. He had suffered ill health for the last few years but insisted on continuing his enthusiastic gardening and his voluntary work of chauffeuring the “old folk” to hospital and elsewhere.

Brucellae are Gram-negative bacteria with a predilection for the reticuloendothelial system and the reproductive tract of cattle, sheep, goats and pigs. In these species brucellosis is of great economic significance because of the resulting abortion and infertility (Samartino et al. 1993; Corbel, 1997; Altecruse et al. 1998). Human brucellosis, caused by contamination from infected animals (percutaneous, conjunctival or nasal infection), is very common and remains a serious health hazard in Mediterranean Europe, western Asia, and parts of Africa and South America (Boschiroli et al. 2001). Raw milk, butter, ice-cream and unpasteurized cheese are also potential vehicles for the transmission of Brucella.